Triple Mikuni plumbing questions

[madkaw]

I have been doing a lot of searching on this and I hope I am just not being redundant here-but, I do have some questions.

What I plan is running a RX-7 pump because I have read many good things about it. I am going to use my existing supply line and a regulator. The regulator is where I get a bit stuck!
I guess I would have no problem running the return line, but not sure of what type regulator to use for that and where to put it in the plumbing? Most regulators I have seen have an inlet and outlet with the return. So do you run that type in a loop set-up before the carbs and attach the return? If you use a return style after the carb, what do you do with the outlet side?
Maybe I am over thinking this, but I only want to order once.

It seems the easiest to just forget the return and run a simple inlet/outlet no return style before the carbs. In either scenerio I would like to have a permantley installed fuel guage. It would be nice to just have the guage right on the regulator. The two port outlet regulators I have seen out there have outlets on the bottom and side, not very convienent location for a fuel guage. Love to see a regulator with two outlets on the side. Plus most guages are 1/8 npt -while most FPR's are 3/8 npt.

Anyway, I will keep searching and hope you guys and shed some light on this.

[steve91tt]

This is the one that I use with my Mikuni's...

http://www.amazon.com/gp/product/B00...ms_ohs_product

However, I don't run a return line so I'm not sure it's much help.

I used to run an in-line pressure gauge but I removed it after I found it to be very inacurate. I may have just got a bad gauge. I mounted it on a t-fitting with two barb conectors for the fuel line and a female NPT connection for the guage.

[madkaw]

Thanks Steve.
Looking at the output pressure of the RX-7 pump(3.5-4.7psi), you might actually get away with no regulator.
I have about come to terms with the fact that when you get down to this little pressure, the selection is small. I don't believe a FPR is sold that has a seperate port for the pressure guage. Now if you go up 1psi to 5, then there is all kind of choices.
I also noted that you can basically make your own adapter for the guage inline, or EBAY of course sells an adapter in one piece for 14$.
I am still playing with the idea of pressurizing the Mikuni's later down the road which will change everything as far as regulators!!
I guess if I go with the Holley with two 'out' ports, I can adapt a guage to one of the outports-though it will take some adapting to be able to see the guage.
It's funny that I have the money ready and I still don't have a firm plan-I guess I should have been doing a better job searching.

[Travel'n Man]

Steve -
Hope this pic helps a little -

I deadheaded my fuel line and have had ZERO problems. I talked with a lot of folks and read a lot to make sure I was not going to get boiling fuel. I have had NO issues at all with my setup and the carbs are a joy every time I fire up my car. I do have a heat shield and I do have a heat barrier on the underside of the heat shield. I used a triple fuel line that works like a charm. I did install a FPR on the passanger engine compartment so if I was working on the carbs I can see the pressure if needed. There is not one thing I would change with my Mikuni set up as of today. I'm glad I did not go with 44's. IMO a lot of folks over carb their cars and then they are chasing continually on how to get the car to run better. I did just install a AFM to my car and really excited about fine tuning with a little plug reading instead of plug reading by itself.

By the way - if I take it easy on my right foot I'm getting 23+ MPG - If I take it hard on my right foot I get under 10 MPG.



My install is documented below if it can help you any and you may want to visit my garage as well:
http://www.classiczcars.com/forums/s...ng-Mikuni-40-s

[LeonV]

Return lines have benefits. You will have cooler fuel, a shorter response time and put less stress on your fuel pump with a functional return line. I'd go with a back-pressure regulated system: tank -> pump -> carbs -> regulator -> tank. This lets the pump flow freely, while controlling the restriction before the carbs in order to maintain steady pressure. This setup allows you to have fuel volume available on demand at all times, i.e. if the need for fuel quickly rises, the restriction gets smaller and more fuel is delivered to the floats immediately.

[steve91tt]

I get fuel boiling if I don't open my hood to let the motor cool down after a hard run in the Texas summer. I also get a stumble if I sit in traffic for extended periods of time. Is this because I don't run a return line?

[madkaw]

Okay, great ideas, but in your case Leon is where I have trouble picking the right regulator or how to plumb. You have what kind of regulator with how many ports? So how is the fuel going in and out and also to the return.
It's easy to picture the FPR before the carbs as a simple in(supply) and out(carbs), but...
your set-up Leon is carbs-- to the "in port" of the FPR and then what?
I'm a visual guy I guess.
Also Mitchell, any closer pics of said FPR set-up-it is hard to see in that pic?

[madkaw]

I get fuel boiling if I don't open my hood to let the motor cool down after a hard run in the Texas summer. I also get a stumble if I sit in traffic for extended periods of time. Is this because I don't run a return line?

Maybe this thread will enlighten that-I don't know. Logic says that keeping the fuel flowing would help negate that, but Mitchell is having no issues and his line still runs along the valve cover-which I want to avoid.

[madkaw]

Still waiting on some dyno numbers!!!

Steve -
Hope this pic helps a little -

I deadheaded my fuel line and have had ZERO problems. I talked with a lot of folks and read a lot to make sure I was not going to get boiling fuel. I have had NO issues at all with my setup and the carbs are a joy every time I fire up my car. I do have a heat shield and I do have a heat barrier on the underside of the heat shield. I used a triple fuel line that works like a charm. I did install a FPR on the passanger engine compartment so if I was working on the carbs I can see the pressure if needed. There is not one thing I would change with my Mikuni set up as of today. I'm glad I did not go with 44's. IMO a lot of folks over carb their cars and then they are chasing continually on how to get the car to run better. I did just install a AFM to my car and really excited about fine tuning with a little plug reading instead of plug reading by itself.

By the way - if I take it easy on my right foot I'm getting 23+ MPG - If I take it hard on my right foot I get under 10 MPG.



My install is documented below if it can help you any and you may want to visit my garage as well:
http://www.classiczcars.com/forums/s...ng-Mikuni-40-s

[LeonV]

I get fuel boiling if I don't open my hood to let the motor cool down after a hard run in the Texas summer. I also get a stumble if I sit in traffic for extended periods of time. Is this because I don't run a return line?

Running a return will help. Heat insulation is key as well, make sure you have a heat shield installed between the exhaust manifold and carbs.

[LeonV]

Okay, great ideas, but in your case Leon is where I have trouble picking the right regulator or how to plumb. You have what kind of regulator with how many ports? So how is the fuel going in and out and also to the return.
It's easy to picture the FPR before the carbs as a simple in(supply) and out(carbs), but...
your set-up Leon is carbs-- to the "in port" of the FPR and then what?
I'm a visual guy I guess.
Also Mitchell, any closer pics of said FPR set-up-it is hard to see in that pic?

It's very simple, the regulator gets placed in-line with your return line. It essentially replaces the small orifice in the stock fuel rail's return line. Fuel comes from the carbs, into the regulator, out of the regulator, to the return line and back to the tank.

I'm sure info on specific regulators is out there, I don't have any part numbers for you but there are a ton out there that will work.

[gogriz91]

I have the same problem and think it's vapor lock. I used to have an electric fuel pump in the engine compartment which seemed to alleviate the issue but moved it to the back because I wanted to clean up the engine compartment. I'm probably going to run a line from the filter through the radiator support then around the front of the radiator and back to the carbs to see if that fixes the issue, BTW I only run an electric pump, no mechanical. (Yeah, it's not an ideal fix but I hope to be getting a set of triples this summer and am looking for a temp fix until that happens)

[Travel'n Man]

Since I am in the mountains of Western North Carolina (elevation 3500 ft) my high summer temp is no more than 85-90 degree's. I'm not battling 100+ degrees outside. I've had my car on some 4 hour drives with no stumbling issues. I'll try to catch a pic of my FPR this evening.

[Carl Beck]

Hi madkaw:
Just another input:
The Holley 12-804 {that steve91tt recommended} is the fuel pressure regulator that was used by BRE on the Baja Z back in 73. Matter of fact the same one is still there working just fine today, and the new one's are still the same.

Holley sells both the 12-803 {higher pressure 4.5-9 psi} and 12-804 {low pressure 1-4 psi}. They are identical with the exception of the pressure relief spring rating. Holley also sells a rebuilt kit with new gaskets and both springs for these regulators.

If you want single lines going to each SU or each Webber etc - - you can mount the regulator on the firewall on the passenger side - put a fuel pressure gauge on the left and an outlet on the right - that feeds a Fuel Distribution Block on the drivers side. You can get fuel distribution blocks for 2 or three outlet lines.
http://www.summitracing.com/search/P.../?autoview=SKU

So if you do change from two SU's to triples - all you need to change is the distribution block. Or just start with the distribution block for three carb's - and use it with a fuel pressure gauge in the center and outlets on each end to the SU's.

I'll mention - that there are two ways of using a "return". First is to return the fuel from the regulator back to the tank. That is provided to let the pump run at its most efficient level. Many regulators have a return built in. The second type of return - returns fuel not used by the carb's - to the tank. That is done to keep the fuel cool in the lines and at the carb's. So the purpose and/or type of return has to be kept in mind.

With a good heat shield between the carb's and headers - most of the time you don't need a return. However - in many area's of the country - or with less than good heat shielding... some applications benefit from the increased fuel flows using a return after the carbs. {like the original fuel rails used by Nissan}.

FWIW,
Carl B.

[madkaw]

So simple I over thinked it!! It just hit me like Mikle Tyson. I guess when I hear return style-I just think a regulator that has a separate return port.

So my triples right now have "T" on every carb for a loop set-up. So I might try and pull off some fuel line bending magic and reposition my supply line along the firewall and give it a straight shot to the carbs. Then coming out the other end of the carbs I will plumb into the 'in" port of the regulator and "out" to the return line and back to the tank.

Wow, Ijust feel like I did something and I haven't done a damn thing-yet!

[Travel'n Man]

Wow, Ijust feel like I did something and I haven't done a damn thing-yet!

I love it when that happens!

[madkaw]

So I might have got a little over zealous here, because I just had another moment-man I'm thick.

So in my possible plumbing diagram below, you would use the Holley 1204 just before the return line?

I look at that regulator and it has 2 outlets and one inlet. I'm gathering I run one outlet to the return line and I can either plug one outlet or plumb a guage there?

So simple I over thinked it!! It just hit me like Mikle Tyson. I guess when I hear return style-I just think a regulator that has a separate return port.

So my triples right now have "T" on every carb for a loop set-up. So I might try and pull off some fuel line bending magic and reposition my supply line along the firewall and give it a straight shot to the carbs. Then coming out the other end of the carbs I will plumb into the 'in" port of the regulator and "out" to the return line and back to the tank.

Wow, Ijust feel like I did something and I haven't done a damn thing-yet!

[gnosez]

Triples with a larger fuel line and a return line, heat shield and coated heater. Wouldn't run the street car any other way. And these are 44mm on a 3.2L so the engine isn't over carb'd.

We run a return line on the 240 race car as well (44mm without large venturi and 13.5:1 compression ratio).

[Travel'n Man]

Failed to comment that my headers are JET HOT coated to reduce temp as well.

[madkaw]

Been all over the Holley web site and it is very informative. There are nice diagrams laying out the plumbing for their FPR's. As far as the 1204 model, it is only to be used before the carb with no return line.

Leon, not sure what FPR works for your setup ? You could use the Holley 1203bp, but the pressure doesn't get below 4psi and Holley states the return should be the same size as the supply.

The Holley site also covers wiring a oil pressure switch and a relay setup for your pump!!

So they way I see it, unless someone can show me otherwise, the only option is the 1204 and not use a return line

[Travel'n Man]

I used the same FPR that Steve91tt mentioned.

I did not put in an oil pressure switch but did set up an inertia switch (with the power relay) to kill the fuel pump if something bad happens. I mounted mine on the firewall of the passenger side. Since the fuel pump is run off the switch power supply and if you have a wreck the only way to stop the fuel pump is to turn the switch off - or - have the inertia switch do it for you on impact. I really did not like the sound of fuel pumping consistently if I was in a wreck so I figured the $80 or so was well worth it...................hopefully I will never need that little gizmo!

Don't forget the fuel filter directly after your tank - I used a Holley 162-551 Fuel Filter

Are you going to use the original fuel rail with the original return - if I was going to do that my plumbing would be:
tank => fuel filter => fuel pump => FPR => inline fuel filter => original fuel rail => carb1 => carb2 => carb3 => original return line (that goes back to the tank).

[LeonV]

Leon, not sure what FPR works for your setup ? You could use the Holley 1203bp, but the pressure doesn't get below 4psi and Holley states the return should be the same size as the supply.

I use the mechanical pump with the stock feed and return lines for my triples. I do have an RX7 pump laying around that I plan on installing sometime...

I'm not sure why you're fixated on Holley regulators. Search around a bit, especially on HybridZ to see what others have run. A "backpressure regulated" system is what you're looking for.

[Mike W]

Steve - Here's another input that I hope will help you (instead of confusing things further).

I run triple Webers, not Mikunis, bit I suspect that a lot of the issues are the same.

I also searched high and low for an appropriate FPR and did find al alternaitve to the Holley. It is from Summit Racing and the P/N is 220065. It has a range of 3-12 PSI, supports one inlet, two outlets, and also has a gauge port. I admittedly have it adjusted to about as low as it will go, but so far it is working great for me. I also used a fuel log to distribute fuel to each of the individual carbs, but was worried about the mounting location that I chose as it was right above the intake manifold and I was concerned about heat and the resulting vapor lock. Surprisingly I have had no issues to date and this is even in the heat of the Texas summer. I do run the MSA headers that are coated as well as a heat shield undert the Webers.

Here's a few pictures of my system. I have all of the details of this in a power point file if this will help you out. Just let me know and I will send it off to you.



Mike.

[madkaw]

Okay. Just laid out big bucks to get this job going. Went with the 1204 Holley FPR and a guage, fuel pump relay, filters, RX -7 pump, CAI piping, filter.

I'm going to just deadhead to the carbs. Ordered some bits I needed for the Mikunis from Wolf Creek so they should be ready to go.

Right now I am resizing some studs for the manifold. The studs that came with the triples seem to short and there is not enough threads in the nuts for me.

This is going to be a pretty involved job!

[Zedyone_kenobi]

I know, it is just awesome to start something and you only have a notion of how you will finish it. Back in college getting my engineering undergraduate, we called this an open ended design problem.

THE BEST KIND!

Have fun madkaw! Keep us in the loop, I am builidng up my triples now too as you know. We should compare notes!