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Thread: Triple Mikuni thread

  1. #101
    Registered User Travel'n Man's Avatar
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    I am moving back to a colder plug - just by one notch. My plug strap is showing signs of dark coloration at the very bottom of the strap where it connects to the body of the plug

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    Life's a journey; enjoy the ride!

    Mitchell
    L28 - N42 Block w/Flat tops - N42 Rebello Head & Cam - Triple 40 PHH Mikuni's - Headers - Recaro Seats -
    R180 3.9 Diff - Close Ratio 5 Speed - Toyota Vented Brake Upgrade w/ Porterfield High Performance Pads & Shoes

    1972 Datsun 240z
    HLS30-75040


  2. #102
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    Thank God we got a second page, it takes forever for my phone to scroll that first page-lol

    I am 99% positive a have an ignition problem= Megasquirt. When plugs 4,5,,6 look carboned on triple carbs, then it's probably ignition.

    I've always ran the 6 with good results.
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    Great thread, very informative!

    Time for me to join in all this fun...

    Just got my wideband (AEM UEGO) up and running, and was pretty shocked at the numbers I was reading...

    Warm idle AFR @ 1000RPM - 11.4
    4th Gear @ 2000 RPM - 12.5
    WOT - 2nd gear @ 6000RPM - 10.5

    A little rich, shall we say?

    Running 44's on a 3.0 stroker.

    Pulling the jets tomorrow to see what I have in there. Had these carbs rebuilt just over a year ago by a reputable shop, so all else should be good.

  4. #104
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    Yes sir- a bit rich !
    Feel free to share you Mikuni experiences- that's how we learn
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

  5. #105
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    Quote Originally Posted by RyanT67 View Post
    Great thread, very informative!

    Time for me to join in all this fun...

    Just got my wideband (AEM UEGO) up and running, and was pretty shocked at the numbers I was reading...

    Warm idle AFR @ 1000RPM - 11.4
    4th Gear @ 2000 RPM - 12.5
    WOT - 2nd gear @ 6000RPM - 10.5

    A little rich, shall we say?

    Running 44's on a 3.0 stroker.

    Pulling the jets tomorrow to see what I have in there. Had these carbs rebuilt just over a year ago by a reputable shop, so all else should be good.
    Do you know your spec's on your set up? Sounds like you need to lean out pilots, and fuels. Let us know what jets you have. Be sure to log all AFR with your data so you know where you are and where you are going.
    Last edited by Travel'n Man; 07-08-2014 at 05:25 PM.
    Life's a journey; enjoy the ride!

    Mitchell
    L28 - N42 Block w/Flat tops - N42 Rebello Head & Cam - Triple 40 PHH Mikuni's - Headers - Recaro Seats -
    R180 3.9 Diff - Close Ratio 5 Speed - Toyota Vented Brake Upgrade w/ Porterfield High Performance Pads & Shoes

    1972 Datsun 240z
    HLS30-75040


  6. #106
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    Just opened up the suckers today to see what the hell was in them...

    Cylinder 1 - 2 - 3 - 4 - 5 - 6
    Main air jet 170 - 170 - 170 - 170 - 170 - 170
    Main fuel jet 140 - 145 - 145 - 145 - 140 - 140
    Pilot Jet 52.5 - 55 - 55 - 55 - 52.5 - 50
    Pilot screw was 2 turn out from seated.
    Last edited by RyanT67; 07-10-2014 at 07:16 PM.

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    Can't log, not set up for it. Have the gauge mounted on the steering column though, so my eye is on it as much as it's on the speedo and tach. Might take the car out into the country for a good rip tomorrow, and record the main cluster while doing so. Would be good to review.

    Either way, looks like I need a higher number for my main air jets from the looks of it? Not sure what's up with the pilot's fluctuating in numbers like that.

    When I bought this car 2 years ago, it ran very poorly. Suspected it sat longer than the previous owner indicated and I took it into a Z-specialist shop to have the carbs cleaned, rebuilt, and properly tuned. It ran me $1350 for this service - I'm questioning that investment now. I knew it was running rich, but couldn't tell just how excessive it was until I got the wideband installed.

    Ah well, the rest of the car is doing well, so I am ready to sink some time into this area and learn all I can.

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    Well getting the same jets in all of them is a good first step. Can't imagine trying to get that thing in balance the way it is. Time to call Todd....

    I have 62.5 pilots, 160 main and 200 airs 34mm chokes and idle screws at 1.5ish in my 44's on a 3.1 stroker

    EDIT : Sorry, the original statement above said. 150 main was actually 160. 150 was an earlier iteration.
    Last edited by zKars; 07-11-2014 at 08:27 AM.
    -----------------------------------------
    Jim
    73 240Z HLS30 149331
    69 510 PL510 77603

    www.zKars.com
    www.calgaryzclub.ca
    Reference materials
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    Quote Originally Posted by zKars View Post
    Well getting the same jets in all of them is a good first step. Can't imagine trying to get that thing in balance the way it is. Time to call Todd....

    I have 62.5 pilots, 150 main and 200 airs 34mm chokes and idle screws at 1.5ish in my 44's on a 3.1 stroker
    What is your AFR at idle, 35 and 60, and WOT?
    Last edited by Travel'n Man; 07-11-2014 at 04:14 AM.
    Life's a journey; enjoy the ride!

    Mitchell
    L28 - N42 Block w/Flat tops - N42 Rebello Head & Cam - Triple 40 PHH Mikuni's - Headers - Recaro Seats -
    R180 3.9 Diff - Close Ratio 5 Speed - Toyota Vented Brake Upgrade w/ Porterfield High Performance Pads & Shoes

    1972 Datsun 240z
    HLS30-75040


  10. #110
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    Quote Originally Posted by RyanT67 View Post
    Can't log, not set up for it. Have the gauge mounted on the steering column though, so my eye is on it as much as it's on the speedo and tach. Might take the car out into the country for a good rip tomorrow, and record the main cluster while doing so. Would be good to review.

    Either way, looks like I need a higher number for my main air jets from the looks of it? Not sure what's up with the pilot's fluctuating in numbers like that.

    When I bought this car 2 years ago, it ran very poorly. Suspected it sat longer than the previous owner indicated and I took it into a Z-specialist shop to have the carbs cleaned, rebuilt, and properly tuned. It ran me $1350 for this service - I'm questioning that investment now. I knew it was running rich, but couldn't tell just how excessive it was until I got the wideband installed.

    Ah well, the rest of the car is doing well, so I am ready to sink some time into this area and learn all I can.
    Ryan-
    I use a good ole' piece of paper in the passengers seat. It will take a lot of different settings to find the best one for your AFR. I would start by leaning out your pilot since you are running a high AFR at idle. Only make one change at a time and log it on your chart. Then (depending on your results) move to your air jet - you may need a little more air...........log that, then move to your main fuel, which sounds like you will need to lean out (go to a smaller size). When you go to different jets only drop 1 size at a time. Don't go from a 65 to a 60, too big of a jump.
    Over the past 2 months I have tried about a dozen setting recording all of them on a spreadsheet so I can keep up with the different combinations and the AFR results.
    Life's a journey; enjoy the ride!

    Mitchell
    L28 - N42 Block w/Flat tops - N42 Rebello Head & Cam - Triple 40 PHH Mikuni's - Headers - Recaro Seats -
    R180 3.9 Diff - Close Ratio 5 Speed - Toyota Vented Brake Upgrade w/ Porterfield High Performance Pads & Shoes

    1972 Datsun 240z
    HLS30-75040


  11. #111
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    Pilot Jet => 0-2%% throttle - cruising - low end power - (higher number equals richer mix)
    Main Jet => 25-100% throttle - Adds or removes fuel from the entire RPM range - (higher number equals richer mix) - top end power
    Air jet => Larger the air jet the more air coming into the Mikuni = (higher number the leaner mix)
    Pump Nozzle => Larger the Nozzle bore size the shorter duration of fuel into the system

    Pilot Screw Setting => This is not an AIR adjustment - this is the adjustment for the amount of fuel/air mix going into the carb (Clockwise = LEANER / Counter Clockwiser = RICHER)
    Life's a journey; enjoy the ride!

    Mitchell
    L28 - N42 Block w/Flat tops - N42 Rebello Head & Cam - Triple 40 PHH Mikuni's - Headers - Recaro Seats -
    R180 3.9 Diff - Close Ratio 5 Speed - Toyota Vented Brake Upgrade w/ Porterfield High Performance Pads & Shoes

    1972 Datsun 240z
    HLS30-75040


  12. #112
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    Here is an example of my worksheet - I can not figure out how to post a spreadsheet to this site:
    As you see I was still a little phat on this setting with my Main Fuel/Main Air

    Date 7-Jun-14
    Main Air Jet (Higher number = Leaner Mix) 200
    Main Fuel Jet (Higher number = Richer) = HIGH SPEED 145
    Pilot Jet (Higher number = Richer) = LOW SPEED 65
    Pilot Screw (Base Setting 1.5 turns out) 2.5
    Venturi Large 32
    Pump Nozzle 0.40
    Bleed Pipe T
    Jet Block 8

    AFR @1,000 RPM Warm Idle => 13.5
    AFR @ WOT @5000 RPM => 13.5
    AFR @ 35 MPH - 3RD GEAR - even pull => 12.6
    AFR @ 60 MPH - 4TH GEAR - even pull => 12.4
    AFR @ 60 MPH - 5TH GEAR - even pull => 13
    Spark Plug Type => BPR6ES-11
    Syncrometer Balance => 4
    Spark Plug Condition => GOOD - DRY

    Notes
    Starting => EASY
    Exhaust Smoke => SLIGHT
    Fuel/Exhaust Smell -> VERY SLIGHT
    Backfire => SLIGHT - ON DECEL

    Low Speed Power => GOOD
    High Power Power => GOOD
    Last edited by Travel'n Man; 07-11-2014 at 04:06 AM.
    Life's a journey; enjoy the ride!

    Mitchell
    L28 - N42 Block w/Flat tops - N42 Rebello Head & Cam - Triple 40 PHH Mikuni's - Headers - Recaro Seats -
    R180 3.9 Diff - Close Ratio 5 Speed - Toyota Vented Brake Upgrade w/ Porterfield High Performance Pads & Shoes

    1972 Datsun 240z
    HLS30-75040


  13. #113
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    Ryan -
    zKars gave you his setting and both you have the same set up........unknowing about cam. You may want to start with his baseline setting (one he posts his ARF - or a pic of his plugs) in yours and start fresh. If you pull your plugs they are going to look very black due to the extreme fuel being dumped on them. You are loosing the 3.1 performance that your engine has to offer. Keep us posted on your results.
    Life's a journey; enjoy the ride!

    Mitchell
    L28 - N42 Block w/Flat tops - N42 Rebello Head & Cam - Triple 40 PHH Mikuni's - Headers - Recaro Seats -
    R180 3.9 Diff - Close Ratio 5 Speed - Toyota Vented Brake Upgrade w/ Porterfield High Performance Pads & Shoes

    1972 Datsun 240z
    HLS30-75040


  14. #114
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    Quote Originally Posted by Travel'n Man View Post
    What is your AFR at idle, 35 and 60, and WOT?
    AFR idle >13.5
    AFR 35 >> 12
    AFR 60 >> 13-14
    AFR WOT >> 13ish
    -----------------------------------------
    Jim
    73 240Z HLS30 149331
    69 510 PL510 77603

    www.zKars.com
    www.calgaryzclub.ca
    Reference materials
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    While we're at it, thought I'd share another Mikuni tuning observation.

    When the tuning was "slightly too lean" like 15-16 idle, 15ish putsing around town and on cruise, 15-16 at WOT, the car never sounded so smooth, quiet, never idled better, it was a dream for my old kinda nasty cammed stroker. This was with 57.5 pilots, and 150 mains.

    Trouble was, it wasn't just the noise and harnessness that was gone, so was the power. The WOT power was slightly hesitant and bucky, just like what you're told when its too lean. No strong pull, obvious faltering. Around town felt "ok" bit it lacked the punch it had before. But the smoothness and quieter exhaust note were intoxicating in some way. I guess I could use this baseline for days when we're cruising on long trips and there are no "fun" parts where you want power, just smoothness and fuel economy. Hardly convenient, and no dang good at all when do get a "look" from some hi-brow in a $50 bazzillion dollar hot rod ... or an actual curve appears on the road ahead. Dang carbs, why can't I hide some injectors in there somewhere....

    So I'm back to 62.5 pilots and 160 mains (see edit above) with carefully tweaked idle screws to get the leanest idle I can stand. Its brasher again, noiser, rougher, but it runs like the perverbial violated primate.... WOT is a total hoot. Stomp it anytime from 2K and it just pulls. AFR''s are 12-13ish at WOT.

    Another observation after careful inspection. The first transition hole is JUST covered by the blades when fully closed, at least on my carbs. Virtually ANY amount of opening exposes that first hole almost immediately. Pretty tough (dare I say impossible?) to get that supposed ideal position where NO transition holes are exposed, just running on ilde screw port fuel, but the blades open enough so that it can idle. Now my blades are hardly pristine and un-touched, my old Q types have seen many miles. They're clean, but the blades don't close all very evenly. A strong light shone from front to back with them in your hand shows a variable amount of light sneaking around tortured blades from barrel to barrel.

    Still this idea that "no transition holes until you actually USE the gas pedal" is pretty darn hard to attain. This explains the option to plug up that first transition hole that I've read about. I don't have a throttle-on stumble, the accel pump takes care of that, but if the pilots are too lean, it starts to show up, as you have to open the screw too far and you steal all the idle fuel before it gets to come out the transition holes. What a crazy balancing act.... Maybe if I have a air bypass valve to the vacuum log to adjust idle. hmmm, more hoses, valves and tubes... It lets more air in, but its dry, so have to increase the pilots..... here we go again!
    -----------------------------------------
    Jim
    73 240Z HLS30 149331
    69 510 PL510 77603

    www.zKars.com
    www.calgaryzclub.ca
    Reference materials
    www.xenonS30.com

  16. #116
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    Jim,

    That last sentence seems like you(Jim) are an organic O2 sensor

    How about this variation:

    Maybe a straw from the tail pipe to a nostril and a motorized fuel height screw controlled by the choke lever (for adding fuel when you need it w/o the jet swap).
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
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  17. #117
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    I'm happy at 13'ish........I was in the 11's and 12's but my plugs were black. I'm happy on the phat side without black plugs!
    Life's a journey; enjoy the ride!

    Mitchell
    L28 - N42 Block w/Flat tops - N42 Rebello Head & Cam - Triple 40 PHH Mikuni's - Headers - Recaro Seats -
    R180 3.9 Diff - Close Ratio 5 Speed - Toyota Vented Brake Upgrade w/ Porterfield High Performance Pads & Shoes

    1972 Datsun 240z
    HLS30-75040


  18. #118
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    Quote Originally Posted by zKars View Post
    Well getting the same jets in all of them is a good first step. Can't imagine trying to get that thing in balance the way it is. Time to call Todd....

    I have 62.5 pilots, 160 main and 200 airs 34mm chokes and idle screws at 1.5ish in my 44's on a 3.1 stroker

    EDIT : Sorry, the original statement above said. 150 main was actually 160. 150 was an earlier iteration.
    Thanks for sharing. I've no idea what I have for internals with my engine, purely the previous owners listing and an old barrett-jackson listing that state the car has a 3.0 stroker in it. Given all the other toys on the car, it's likely true. I should go ahead and at least see what cam I am running though.

    I think I will head towards the jets you have posted though, shouldn't be too far off what I need. I am running a 34 choke already.

    Quote Originally Posted by Travel'n Man View Post
    Here is an example of my worksheet - I can not figure out how to post a spreadsheet to this site:
    As you see I was still a little phat on this setting with my Main Fuel/Main Air

    Date 7-Jun-14
    Main Air Jet (Higher number = Leaner Mix) 200
    Main Fuel Jet (Higher number = Richer) = HIGH SPEED 145
    Pilot Jet (Higher number = Richer) = LOW SPEED 65
    Pilot Screw (Base Setting 1.5 turns out) 2.5
    Venturi Large 32
    Pump Nozzle 0.40
    Bleed Pipe T
    Jet Block 8

    AFR @1,000 RPM Warm Idle => 13.5
    AFR @ WOT @5000 RPM => 13.5
    AFR @ 35 MPH - 3RD GEAR - even pull => 12.6
    AFR @ 60 MPH - 4TH GEAR - even pull => 12.4
    AFR @ 60 MPH - 5TH GEAR - even pull => 13
    Spark Plug Type => BPR6ES-11
    Syncrometer Balance => 4
    Spark Plug Condition => GOOD - DRY

    Notes
    Starting => EASY
    Exhaust Smoke => SLIGHT
    Fuel/Exhaust Smell -> VERY SLIGHT
    Backfire => SLIGHT - ON DECEL

    Low Speed Power => GOOD
    High Power Power => GOOD
    Very good idea!! Thanks for the template, ideal!

    Rookie question for you guys: Is it normal to lean out a lot when you let off the gas pedal, or drop a gear on deceleration? I drop down towards 16, sometimes as low as 17 when doing so, and get a pretty large amount of backfire. I built some det cans to listen in better on the engine, and don't seem to hear any detonation/ping though, thankfully.

    As far as ordering jets, I think I need to build a solid base set of them for when I eventually take the car to the dyno to nail down the tuning and timing. So how about sets of:
    Main fuel: 145(3), 150, 155, 160
    Main air: 180, 190, 200
    Pilot: 55 (3), 57.5, 60, 62.5

    I'm sure Todd will keep me in the right on this. Don't mind spending the money, just want to get it done right and have some room to play - and being in Canada, it's a hassle to continually order and suffer shipping charges.

  19. #119
    Rust Free'ish zKars's Avatar
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    Ryant67, yes, it normal. Throttle blades snap shot, no air flow = no fuel, = high AFR. The back fire is something else, ie residual fuel in the system getting ignited by elevated temps in the exhaust. Definite sign of being too rich most of the time.

    I used to get that engine braking down a hill. Sounds all racy and stuff, like I have a bad ass motor. Even got little flames some times. People point and stare, and I'm sure they are thinkin' "that guy is cool with that fast car"... That is what they were thinking wasn't it? Right?

    Don't worry about spend too much on jets. I'll relieve you of your burden and re-line your pockets when you're done jetting.
    -----------------------------------------
    Jim
    73 240Z HLS30 149331
    69 510 PL510 77603

    www.zKars.com
    www.calgaryzclub.ca
    Reference materials
    www.xenonS30.com

  20. #120
    Registered User madkaw's Avatar
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    Quote Originally Posted by zKars View Post
    While we're at it, thought I'd share another Mikuni tuning observation.

    When the tuning was "slightly too lean" like 15-16 idle, 15ish putsing around town and on cruise, 15-16 at WOT, the car never sounded so smooth, quiet, never idled better, it was a dream for my old kinda nasty cammed stroker. This was with 57.5 pilots, and 150 mains.

    Trouble was, it wasn't just the noise and harnessness that was gone, so was the power. The WOT power was slightly hesitant and bucky, just like what you're told when its too lean. No strong pull, obvious faltering. Around town felt "ok" bit it lacked the punch it had before. But the smoothness and quieter exhaust note were intoxicating in some way. I guess I could use this baseline for days when we're cruising on long trips and there are no "fun" parts where you want power, just smoothness and fuel economy. Hardly convenient, and no dang good at all when do get a "look" from some hi-brow in a $50 bazzillion dollar hot rod ... or an actual curve appears on the road ahead. Dang carbs, why can't I hide some injectors in there somewhere....

    So I'm back to 62.5 pilots and 160 mains (see edit above) with carefully tweaked idle screws to get the leanest idle I can stand. Its brasher again, noiser, rougher, but it runs like the perverbial violated primate.... WOT is a total hoot. Stomp it anytime from 2K and it just pulls. AFR''s are 12-13ish at WOT.

    Another observation after careful inspection. The first transition hole is JUST covered by the blades when fully closed, at least on my carbs. Virtually ANY amount of opening exposes that first hole almost immediately. Pretty tough (dare I say impossible?) to get that supposed ideal position where NO transition holes are exposed, just running on ilde screw port fuel, but the blades open enough so that it can idle. Now my blades are hardly pristine and un-touched, my old Q types have seen many miles. They're clean, but the blades don't close all very evenly. A strong light shone from front to back with them in your hand shows a variable amount of light sneaking around tortured blades from barrel to barrel.

    Still this idea that "no transition holes until you actually USE the gas pedal" is pretty darn hard to attain. This explains the option to plug up that first transition hole that I've read about. I don't have a throttle-on stumble, the accel pump takes care of that, but if the pilots are too lean, it starts to show up, as you have to open the screw too far and you steal all the idle fuel before it gets to come out the transition holes. What a crazy balancing act.... Maybe if I have a air bypass valve to the vacuum log to adjust idle. hmmm, more hoses, valves and tubes... It lets more air in, but its dry, so have to increase the pilots..... here we go again!
    My observation has been the opposite. Engine purrs and sounds so much smoother with a rich mix. Exhaust sound is fuller if that makes sense.
    I really don't think these carbs were designed for lean driving. Probably has much to do with the Tau layer. Love my Mikunis but ready to tune without my hands smelling like gas
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

  21. #121
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    Just remember when buying your jets they come in two different head mm sizes. If you buy anywhere other than Todd - be sure to tell them you want the smaller mm size

    Here is what I have collected so far:
    Main Jet Pilot Jet Air Jet
    140 57.5 200
    145 60 195
    150 62.5 190
    155 65 185
    160 180
    Life's a journey; enjoy the ride!

    Mitchell
    L28 - N42 Block w/Flat tops - N42 Rebello Head & Cam - Triple 40 PHH Mikuni's - Headers - Recaro Seats -
    R180 3.9 Diff - Close Ratio 5 Speed - Toyota Vented Brake Upgrade w/ Porterfield High Performance Pads & Shoes

    1972 Datsun 240z
    HLS30-75040


  22. #122
    HS30-00352, HS30-101370 240znz's Avatar
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    Hey all,

    Excellent thread. Lots of valuable info within.

    I'm about to send my 44's to a local carb shop for stripping and rebuilding and while they are a away, I'd like to start thinking removing the shaft throttle system to a cable version.

    Has anyone written up or got a few good pictures of this type of conversion.

    Also running stock fuel pump, should I install a electric pump at the tank? Cabling easy to run still. I see plenty of engine bays with fuel pressure gauges and O2 sensors in headers. Is there any preference to which header primary the O2 sensor is fitted?

    Cheers

    James
    Zed not Zee

    HS30-00352 still being rebuilt (year 6)
    HS30-101370 chopped in half

    CZCC #1608

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    Here you go - great improvement as well

    http://www.classiczcars.com/forums/c...questions.html
    Life's a journey; enjoy the ride!

    Mitchell
    L28 - N42 Block w/Flat tops - N42 Rebello Head & Cam - Triple 40 PHH Mikuni's - Headers - Recaro Seats -
    R180 3.9 Diff - Close Ratio 5 Speed - Toyota Vented Brake Upgrade w/ Porterfield High Performance Pads & Shoes

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    I would comment that my direct linkage works flawlessly. I couldn't imagine cable being any improvement. It can be done!
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    I need some insight here guys. Having an issue with running rich on certain cylinders. Primarily #4 runs rich, but 3 is fine. How does that happen that one half of a carb runs rich. Floats have been checked as well as fuel pressure. Ignition has also been eliminated from the equation. I also did a coolant pressure test for a blown HG. Cylinders read 180-190 on cylinders 4-6
    Getting ready to pull carbs off completely to look everywhere.
    These carbs have been very consistant as far as pilot adjustments, but now I have to turn #4 way in to keep it from fouling out. I will be blowing out passages to I guess. I have been having the biggest issue with cylinders 4-6.
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
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    Is it possible a different circuit is leaking such as a cold start/choke? I'm not sure about Mikuni's but it can happen to dcoe's.

    Also check jet diameters. A poorly drilled made in mainland china jet could be the culprit. '

    You can move jet and e-tubes around to see if the problem moves to eliminate items.
    Last edited by Blue; 07-18-2014 at 11:28 AM.
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    Thanks-keep any ideas coming.
    Chokes-maybe-but I would think it would foul both sides are carb, and I did check them
    Jets have all been used before with no issues.
    I could swap around e-tubes I guess. Not sure what could go wrong with them.
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
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    Any progress Steve? For the first time in 2 years, I had one of the needle valves stick in the seat, due to some microscopic dirt build up.. though like most things I would think that should affect both cylinders per carb. If the e tube swap and making sure all the jets are tight on the block didn't get anywhere, maybe swap plugs between cylinders to see if the problem follows the plug?

    Came across this thread while searching, good to see it's still going. Here's my jet logs to further contribute;

    L28 stock bottom / N47 maxima head
    Schneider regrind on stock cam to 270/280 .460
    Pilots 62.5
    Main 140
    Air 190

    Pilots out 1.75 or so each

    Warm idle AFR @ 800RPM - 15 - 16
    Cruise - 12 ish
    WOT - 4th @ 6000RPM - 13.5 - 13.7


    Now with a Cartech blow through boosting 9psi

    Pilots 62.5
    Main 145
    Air 180

    Warm idle AFR @ 800RPM - 15 - 16
    Cruise - 11.5 ish (off boost, light throttle in 5th will induce 1 to 3 psi, which will lean it out to 12 - 13, need this transition)
    WOT - 4th @ 6000RPM - 12 ish

    Still fiddling and gonna try 150 main this weekend to get my WOT down to 11.5, going to leave everything else the same.

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    The short answer -No

    I messed the carbs all day. After seeing #2 looking fouled I decided I needed to tear them all down and put some compressed air to things. In the process I didn't see anything that I could attribute to any of my problems. There was the slightest bit of sediment in the bottom of the carbs.

    I put everything back together and and got it running. It's still not right, but once again I can put my finger on it. When I went to synchronise the carbs #4 was hardly drawing air compared to #3. It was off by quite a bit. The engine didn't idle to terrible, but not like it used to. I finally just said WTF, I'll drive it and see how it feels. Well it still not right, hell it even back fired once getting on it. Seems to be lacking power . The AFR's didn't jive with the known jet settings and they seemed a bit erratic.
    I pulled the plugs afterwards and none were fouled and they didn't look too bad .



    Not sure what I'm going to do next. I will probably drive it again tomorrow weather permitting. Getting really discouraged and pissed with the whole matter. This seems to be dragging on to the point that i don't remember how I got here. This car used to run fantastic.
    Last edited by madkaw; 07-25-2014 at 07:27 PM.
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    Quote Originally Posted by Kennymonster View Post
    Warm idle AFR @ 800RPM - 15 - 16
    Cruise - 11.5 ish (off boost, light throttle in 5th will induce 1 to 3 psi, which will lean it out to 12 - 13, need this transition)
    WOT - 4th @ 6000RPM - 12 ish

    Still fiddling and gonna try 150 main this weekend to get my WOT down to 11.5, going to leave everything else the same.
    15-16 is way lean at idle - and IMO 11.5 is too phat - your plugs will be black with soot.
    Life's a journey; enjoy the ride!

    Mitchell
    L28 - N42 Block w/Flat tops - N42 Rebello Head & Cam - Triple 40 PHH Mikuni's - Headers - Recaro Seats -
    R180 3.9 Diff - Close Ratio 5 Speed - Toyota Vented Brake Upgrade w/ Porterfield High Performance Pads & Shoes

    1972 Datsun 240z
    HLS30-75040


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    It seemed that a fatter idle made for easier start ups for me, but if you can get away leaner-go for it. Don't forget Mitchell, he is boosted. Want to keep things on the rich side.
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    Yup, ideally I'd like to have a leaner cruise to rich tip in, but with forced induction (now running 10psi after yesterday's main jet to 150, air still at 180), partial throttle is the biggest issue for me. Basically have to tune for WOT to be low 11's no matter what, as well as keeping it under 13 during transition period, which has been the trickiest part. Ended up gapping the ngk 7's down to .035 even with MSD to avoid any misfire.

    Did some fiddling with pilot screws adjustment on 62.5's, now it's at around 14 on idle, I do have some problems on cold start though.. not sure why as it seems to be getting too much fuel at crank, having to hold the pedal pegged & crank couple times to have it catch. When I was NA it started right up with couple accel pumps, but then again I was running .045 gap on ngk 6's.
    Last edited by Kennymonster; 07-26-2014 at 02:03 PM.

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    Well after running the engine again and seeing #4 draw much less air then it's next door neighbor#3, I decided to rip them all off and pull the intake too. Of course the intake gasket was fine, which I thought it would be. The car didn't run it had vacuum leaks, but I'm getting desperate.
    I did check the butterflies on 3&4 and they matched up beautifully.

    Now I stare at my engine thinking what;s next. Not much in the way of evidence to justify pulling the head, but I think my carbs are okay. I did notice looking down in the intake runners of 3&4 that there was a lot of soot? on the inner walls of both cylinders. When I say inner, I mean in respect of each other. No other cylinders look like that.

    Kenny,
    I fought transition with these carbs and thought I won with the bleed pipe mods. I don't think those mods have anything to do with my issues now. I would try and go as big as possible on my pilots if I were you. I don't understand why my motor/cam wants such big pilots, but it works well.
    I think it is mostly the Schneider grind, but I've run 70's on my motor. I run 67.5's now and it's just a L24!!
    The bigger pilots might help you bridge the transition gap better, then maybe drop your main air's. I have smaller main airs if you need any. I bought all the way down to 160's to fight the transition issue. I'll never use them.
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    ^If the compression on the cylinders check out, I guess check the valve clearance? I feel like these carbs are pretty stout and hard to believe they'll start fouling all of a sudden for no reason, I wonder if your lashes went out of adjustment.

    As for me, I have a set of 65 pilots but afraid that'll just enrich my cruise more than it already is, basically at a level of compromise at this point. I wonder if all that intercooler piping and whatnot is impeding off boost air flow and making my afr richer than it would be at cruise, i.e. compared to just open velocity stacks sucking in. My buddy just ordered a set of rebuilt 40's from Todd for his L24 on a smallish cam, and he received 62.5 and 65 for baseline, apparently that's where the starting point should be anyways.

    I have 170 to 220 for air and mains ranging from 120's (don't ask lol) to 165, I see that you're a frequent shopper with Todd as well haha. My current tune right now at 150 main /180 air / 62.5 pilot is actually pretty good at 10psi, I'll probably leave it unless I run into issues, haven't really done too many pulls at 4th gear yet since it hits 3 digits pretty quick now ;p

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    Ken -
    Tell us about your build so we can keep up with your tuning. Pics are always welcome!
    Life's a journey; enjoy the ride!

    Mitchell
    L28 - N42 Block w/Flat tops - N42 Rebello Head & Cam - Triple 40 PHH Mikuni's - Headers - Recaro Seats -
    R180 3.9 Diff - Close Ratio 5 Speed - Toyota Vented Brake Upgrade w/ Porterfield High Performance Pads & Shoes

    1972 Datsun 240z
    HLS30-75040


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    Quote Originally Posted by Travel'n Man View Post
    Ken -
    Tell us about your build so we can keep up with your tuning. Pics are always welcome!
    Sure thing, I'll try to be as brief & concise as I can, and attempt to avoid turning the thread about me / my setup. I figure some of this will be useful information for anyone going this route anyway, hybridZ has some scattered info on blow-through's but nothing comprehensive, I should really put my notes together and post the build log.

    Current Mikuni settings, with 10 psi on the t3/t04b turbo that came with the Cartech kit (sorry not much details on the turbo itself, had it rebuilt due to it destroying itself during tuning)

    Mikuni 44's
    34mm venturis
    150 main
    180 air
    62.5 pilot
    45 pump

    For those not familiar, the kit is basically an 80's Corky Bell / Bell Engineering creation, not too many around these days. I came across it randomly when someone offered it to me out of the blue, at a bad time to resist since I had a local friend/competitor who was about to turbo his Miata.

    If you do a search for this online, you'll probably see a handful having ran it in the past, but switched over to EFI, as well as a bunch talking about wanting or running it, and never following through (in typical internet fashion of easier said than done). There are also tuning concerns stated, or the lack there of. I have to admit that I didn't know much about it, but still wanted the challenge based on the assumption that if the kit was being made and sold at some point, it had to have worked.

    It took some time to really get it to run decent, not because of the jetting, but more to do with providing adequate fuel delivery and addressing the plethora of issues that came with pressurizing the carbs, against their intended purpose.

    Here's a quick cliff notes to save headaches for those researching this route:

    - Get an EFI fuel pump + bypass style regulator with boost reference + run a bigger return line. This will maintain 3.5 needed for the carbs, and with the fuel regulator upping the psi of fuel 1:1 ratio with the boost applied, it'll ensure that the float bowls stay full. i.e. Fuel pressure needs to be at 13.5 to have 3.5 psi at the carbs + 10 psi of compressed air coming in.

    - Ignition timing, I think this was one of the advantages of trying this set up in 2014, as opposed to 1985. With the MSD 6AL unit, I was able to get an additional MSD module that connects to it, a 'boost timing master.' With the boost reference, it will retard the ignition timing between (1 to 3 degrees, adjustable), per each pound of boost, and you can also choose at what point the retarding kicks in, between 1 to 5 psi. This allows me to maintain 15 degrees base timing at idle, mid 30's at cruise when off boost, and total advance back down to 20 at full boost.

    The kit out of Corky Bell's literature:




    Replaced that ridiculous 80's wastegate on the left with a newer model, same brand:




    3 port Mallory regulator with boost reference: it actually has total of 4 ports for inlet/outlet, and the return which comes out the bottom. This worked out nicely for the triples, since I have 1 port as feed, the 3 remaining outlets have dedicated lines going into each carb to prevent any starvation.




    Shot of my engine bay as of today, since there's no ECU, everything has to be referenced the old fashioned way, with vacuum/boost. Using a short runner Mikuni intake manifold, I'm using 4 out of 6 vac ports which most NA setups will retain the hex plugs/not use. Fuel pressure and ignition timing is referenced at the plenum, to achieve earlier and simultaneous signal for each. Only mods to the carbs at this point, are changes to the jetting above, and making slightly thicker gaskets out of cork material for the jet covers, to make sure there's no pressure leak under boost (could probably order new sets from Todd... but I'm afraid they'll be something like 20 bucks each)


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    It's an accomplishment for sure to make the pressurized Mikuni's work. I think the programmable ignition is mandatory to keep this builds from blowing up.
    I thought about pressurizing mine for a while, but since I am having issues with just NA, I think I will stick to FI for turbocharging
    It definitely looks impressive under the hood Kenny
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    ^Yup detonation kills motors, not boost. I had the wastegate hooked up incorrectly on one run, accidentally hit 16 - 20 psi few times, but with the afr/ignition in check, it pulled like a space shuttle.

    If I can get this to work after many frustrated nights, I know you can figure out your issue Steve Will be waiting on updates!

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    Ken-
    Have you dyno'd?
    Life's a journey; enjoy the ride!

    Mitchell
    L28 - N42 Block w/Flat tops - N42 Rebello Head & Cam - Triple 40 PHH Mikuni's - Headers - Recaro Seats -
    R180 3.9 Diff - Close Ratio 5 Speed - Toyota Vented Brake Upgrade w/ Porterfield High Performance Pads & Shoes

    1972 Datsun 240z
    HLS30-75040


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    ^I have not, but will soon. I always go to the same place so it should show a pretty accurate before/after comparison, I put down 150/150 as NA, expecting low 200's with the boost.

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    No updates except frustration! On vacation in Irvine CA right now-so stepping away and also waiting for parts from Todd. I need to do more carb swapping- as far as position- to verify my issues.
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    ^You're only couple of hours from me, how long are you sticking around in so cal / any plans to attend ZCon next week? The San Diego Z club folks are going nuts getting everything set up, I'll be volunteering at the zcon AutoX on the 9th also.

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    Not long enough
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    Going to do some jetting this weekend.. at 150 main /180 air, 1st/2nd gear is dead on 11.5 but after getting hot (as in after 8 laps), it's leaning out too much in transition in any high load / high gears, 3rd/4th/5th.

    I threw in 160's last night for the hell of it, pulled like a mother in 3rd/4th without leaning but saw the AFR dip down to 9's when main's kicked in and settled in 10's at WOT. I'm thinking of going back to 150 main, but trying 170 air to see how much effect it would have, hoping for lot earlier transition than the 180's to keep everything smooth.

    Edit: Got impatient and just went out for a 4th gear pull with 150 fuel / 170 air... transition was ok with WOT at 4th around 12 AFR at 6000, this was 8 pm in the evening though. I'm sure it'll lean out in the day when it gets hotter. The 20 gap between main and air seems to be the trick?

    Just ordered 155 main and 175 air's from Todd, hoping for rock solid 11 AFR :P
    Last edited by Kennymonster; 08-14-2014 at 09:03 PM.

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    Those jumps in jetting sizes are too big. I found with my NA that a full 1.0 add was worth over a point on the AFR's. You might get it with the 155's.
    Man I should would like to ride in that 'monster'!!

    Don't forget to calibrate your O2 sensor often. You don't have much room for error.
    Last edited by madkaw; 08-15-2014 at 12:22 AM.
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    Yeah the 160's were an experiment to see how it behaved under super rich condition, under load, that gave me an insight for pilot to main transition under high gear / boost.

    Been just informed that Mikuni air jets only come in 10's, not 5 increments??? Bah, I'll try the 155's with both 170/180 airs I guess.

    I think my AEM unit does a self calibrating routine at start, or it seems like. Next time you're out here on the West coast, holler and we'll go for a drive!

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    If my son goes back there for Nationals at Irvine - I will take you up on that offer.

    I noticed that the smaller main air jet richens the final WOT mixture
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    Got the 155 main / 170 air combo in today, took care of the transition problem for high load @ 3rd / 4th gear

    The smaller air corrector seems to have done the trick, mains kick in lot earlier and the 'lean spike' doesn't go past 12, at WOT it's at 11.2 to 11.3 under 4th gear pull to 6000.

    Car feels happy with the nice fat mixture.

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    Glad you nailed your mixture. It seems these engine like fuel!!
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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