Triple Mikuni Fuel Line Set-up

[Travel'n Man]

To all Triple Mikuni Owners:

Please share your knowledge and tell me what size fuel line you ran to your triple Mikuni's...........thanks in advance!

40mm Mikuni's - Wolf Creek Racing Rebuilds

I have been told: (Todd @ Wolf Creek Racing):

• Remove the current fuel rail
• Remove the current Mech Fuel Pump
• No return fuel line required

Run:

• Tank to-
• In line Filter to-
• Electric Fuel Pump (5-9 psi) to-
• Fuel Pressure Regulator 3-3.5psi to-
• Fuel Filter to-
• Carb-Carb-Carb- dead head at end
• Heat Shield - yet to be fabricated - (does anybody have one you would like to sell - if so PM me)

Todd is jetting and setting for my engine particulars and driving style (show and weekend cruising - never to be tracked). I elected not to go with the 44's due to just really not needing the extra power and air.

Please post your Mikuni pictures so I can see your fuel line set up and the method you ran it -I know I want to keep the fuel lines away from the block and heat as much as possible - I think I am going to use a black braided fuel line like:

http://www.k-tuned.com/store/product...products_id=65

Please share your fuel line sizing and any insight you may have for me with my upcoming adventure with Mikuni's

[LeonV]

I'm not sure what size hose I'm running, but it is slightly wider than the stock feeds to the SUs. As for the lines, I don't see why a return line would be bad and the Z is already set up for it anyway, and why remove the rail for that matter. I kept the fuel rail (and the mechanical pump as well) and am using the return on my triples.

My suggestion:
Tank > Filter > Mechanical pump > Rail > Hose into front carb > Connect carbs > Last carb feeds back into the rail > Return

If you want to run a fuel pressure regulator, then place it after the carbs with a return line present and you now have better regulation and fuel flow since you are regulating the back-pressure and have a bypass for excess fuel. Only excess fuel goes past the regulator instead of the method you mention, which would put a restriction without a bypass and effectively heat the fuel before it even gets to the engine bay. Plus, with a dead-headed setup the fuel then has nowhere to go and further heat up compared to a return line and a back-pressure regulated system.

Of course, I am not saying that your setup won't work and I'm sure many have used it and were okay with doing so. However I prefer the better option especially since the car already has the required provisions. If your Z is just a street cruiser then you probably won't have a problem with the way you were originally told.

[240znz]

Nissan made/makes a triple carb fuel rail without a return so you don't need one either. But there is no point removing the stock return steel line if you don't need to. The stock fuel line will deliver plenty of go juice for your 40's.

[LeonV]

Nissan made/makes a triple carb fuel rail without a return so you don't need one either. But there is no point removing the stock return steel line if you don't need to. The stock fuel line will deliver plenty of go juice for your 40's.

Right. As I said, it'll work, but a return line is better.

[ChrisZ]

Nissan made/makes a triple carb fuel rail without a return so you don't need one either. But there is no point removing the stock return steel line if you don't need to. The stock fuel line will deliver plenty of go juice for your 40's.

Like mine

[Travel'n Man]

Thanks to all that have posted so far!

Chris - can you tell me about your fuel rail, heat shield, and the size of your fuel line please?

[d240zx2]

I ran a 3/8" hard line from a filtered electric pump at the tank into braided Aeroquip line, through filter, then to fuel block, then to each carb. Gauge installed on block. No return line, no mechanical pump. No heat problems. Fuel pressure <6 psi.

Hope this helps.

Frank

[Travel'n Man]

Frank -
Great looking setup and I'm sure she runs great! How did you attach the fuel block?

[d240zx2]

Bolted to the intake/exhaust bolts from the head.

I was quite surprised that the heat soak from the head/exhaust didn't boil the fuel, but it's worked quite well since early last summer. This car has never exhibited the vapor lock problems that other Zs have had. I don't really know why, either.

[Travel'n Man]

I'm trying to do as much research as possible so I can plan out my fuel distribution and keep things as cool as possible. I'm really surprised that Nissan ran the original fuel rail where they did. I may come across the front of the block (by the water pump) and dead head to the carbs with no return. Todd at Wolf Creek Racing said to do away with the current rail and return system. The new system would only have 3.4 to 4 psi and if I can keep the fuel away from the intake area then the hot fuel issue should no be an issue (hopefully).

Frank - what did you do for a heat shield?

[d240zx2]

The Mikunis came with a heat shield under the carbs. You can see it in the third photo.

[Travel'n Man]

So far I can only find one heat shield that is made with a "lip".

http://www.zccjdm.com/catalog.php/az..._SOLEX_MIKUNI_

I reviewed hundreds of internet sites - links -youtube postings. It's amazing how many setups do not include a heat shield. I would really think that would be a necessity, not an option.

[fixitman]

Another arrangement to consider is shown in the attached photos. The premise for my resto/mod was "how would the factory upgrade an early 260Z", if they were to offer a moderately higher performance street model. Keeping that thought in mind, the carb system includes a factory NOS electric fuel pump with filter, mechanical fuel pump, custom fabricated fuel rail and balance tube.

The fuel rail utilizes the original brackets, modified as required, and stainless steel tubing. The rail includes lines for fuel supply and return, vacuum for the distributor vacuum advance and vapor canister, and canister purge. The return line contains the flow restrictor from the original fuel rail.

If you look carefully under the carbs in photo ending in 007, you'll see two heat shields. The one directly under the intake manifold is either from a 240 or 260Z. The other shield came with the Mikuni kit. The shields overlap and are bolted together.

The rubber sleeve fuel clamps for the SS braided hose are an British car item.

Hope this helps.

FixItMan

[Travel'n Man]

David-
Thanks for sharing your set up - looks great. I have noticed on other posts here and Hybridz that states that we should not have a vacuum from the distributor set up - (I was planning on leaving my unattached and working on my timing setting:

Run more initial timing

• 12-14 degree advance @ 1000rpm
• 36 degree total by 3000 rpm

What are your thoughts and how is your timing curve?

[fixitman]

David-
Thanks for sharing your set up - looks great. I have noticed on other posts here and Hybridz that states that we should not have a vacuum from the distributor set up - (I was planning on leaving my unattached and working on my timing setting:

Run more initial timing

• 12-14 degree advance @ 1000rpm
• 36 degree total by 3000 rpm

What are your thoughts and how is your timing curve?

If I remember correctly, the tech advanced the timing a little but I don't know the particulars.

Dave

[ChrisZ]

Mitchell, sorry for my late reply, as for fuel lines, i run the stock lines to the mechanical pump, from there it run to the JDM fuel rail and from the rail i use 8 millimeter hoses to the carbs, works fine.
The heat shield, is a thin pice of aluminium sheet, i bend in a shape very close to the one in the link you posted, simple and work fine, no heat issues.

Chris

[Travel'n Man]

Chris -
Thanks for the info on the sizing - your set up looks great - I'm really fired up about this project!

A few questions for you please:

• Are you running an vacuum on your dist advance?
• Are you deadheading your fuel line or using a return (I believe the JDM deadheads).
• Do you have another JDM fuel rails -those things are tough to find!!!''
• Any recommendations on my set up?

Thanks for you assist!

[RIP260Z]

Mitchell,
I think I sold Chris the fuel rail... anyway, it is the same as what I have.

Mine pictured is an after-market produced one, which I saw sold on Yahoo Japan. I think this is a copy of what was available in the S30 Sports option list, e.g for Mikuni, back in the 1970's. As you see I am running a return line. The return line is smaller than what supplies the carbs. I also put a reducer inside the pipe, the gives something the fuel can pressurize against (rather than running the same dia. fuel pipe) but still let fuel return. I have a small cylinder of brass pushed in, with a 1mm hole drilled through it. I am trying to replicate the system found on the end of the OEM fuel rail.

Hope that helps
Ian

[ChrisZ]

Wot are you saying Ian, is it not a original Nissan fuel rail, but some kind of knock off !!.... who cares.

Mitchelle.
No vacuum, i'm planning on putting on a balance bar on, hence the brass plugs on the bungs, the bungs have been milled and tapped and the balance bar will also be tapped for the PCV.

Deadheading as Ian say

I do not have another but now you know where to look.

I will recommend you to use the stock fuel rail, if the connections on your carbies is T connections, i have seen it be done many times before so it must work, you should focus on getting a solid linkage, unless it is solid already.

Chris

[Travel'n Man]

Great info guys! I'm sure this info will assist all that are piecing this puzzle together as well as myself. Once I finalize my set up I will post the details. I do believe a return line is the best for the performance as well as a heat shield of some sort.

There must not be a lot of Mikuni owners out there since we have only had a few responses back on this subject.

[ChrisZ]

Can't say, mine are Dell-ortos

[Z-point]

My old set-up

[gnosez]

Once I finish up this field project from hell, I'll post pictures from my street 240 w/44's and our 240 race car with the BSR taper bored 44 to 50mm Solexes. Gotta go back to work...but the race car will be in Savannah for ZCON 2011.

[spitz17]

My current set up on a 3.0L Rebello Stroker

[Travel'n Man]

As Dave Rebello would say "Bitch'n!!"

[Travel'n Man]

Update -

Adding a 100 micron Holley Fuel Filter 162-551 between the tank and the fuel pump. I did have an overflow challenge on one of my carbs due to the needle valve sticking open. Naturally it was the carb over the header and the raw fuel was pouring right on top of the header - then I had the brainstorm of cupping my hand to catch the fuel - well, that was not a very good idea either if the header would have caught fire my hand full of fuel would have been right there with it. Looks like I'm going to be in the market for a fire extingisher as well.............just in case.

Anyway - there is a project for next winter - pull the tank - clean & seal!

[Bonzi Lon]

A fire extinguisher is mounted behind the driver's seat of my 240Z. Even though it is a single purpose tool, it is still cheap insurance.

Bonzi Lon

[Travel'n Man]

Agreed!

[steve91tt]

Wow, glad both you and your Z are alright. I'm ordering an extinguisher today.

[LeonV]

A fire extinguisher is mounted behind the driver's seat of my 240Z. Even though it is a single purpose tool, it is still cheap insurance.

Bonzi Lon

I have one in every car, with the Z's being behind the passenger seat for easier access while sitting in the driver's seat.

[Mike W]

A couple of questions for D240zx2 (frank I believe).

So I have a similar setup on my 260Z with triple Webers and have been wanting to change out the rubber lines I have now with a braided AN setup with a fuel distribution block. Your installation is the closest I have seen to what I am looking for (and yours looks great by the way). I have a few questions that hopefully you can help me with:

1. Where did you get the bracket to mount the fuel block to the bolts on your intake manifold? Was this custom made or were you able to purchase a bracket to start with even though there might have been modifications required?
2. You indicated that you used only an electric pump by the fuel tank. Did you need to install this or was it already there? Also did you need to do anything specific to get the pump to run all of the time? I know that on my 260, the electric pump does not start running until the engine reaches 600 rpm so I also have a mechanical pump in my system as well. If I went with a setup similar to yours I would need to find a way for the pump to run as soon as the key was turned on but also find a way to disable it in the case of an accident (ie low oil pressure or something similar). I assume that you completely removed your mechanical pump and just used a block off plate instead.
3. How did you make the transition from the hard line coming from your tank / pump to the AN fittings? Did you use the original hardline installed on the car or did you run a new one? How did you connect the two together?


Thanks in advance for your help. Your system looks awesome and so I appreciate your help in getting mine to look similar.

Mike.

[conedodger]

Mitchell,
I'm wondering why not use the mechanical pump and why not use the return line. What were the reasons given? One would think that fuel starvation would be more of a problem than too much fuel. As long as you can maintain the small amount of fuel pressure needed for Weber/Mikuni/Solex/Dellorto carbs a return line should not be a problem.

[d240zx2]

Sorry for the LARGE delay in answering this publicly... I hope our PMs have answered your questions sufficiently....??

Frank

[Travel'n Man]

Mitchell,
I'm wondering why not use the mechanical pump and why not use the return line. What were the reasons given? One would think that fuel starvation would be more of a problem than too much fuel. As long as you can maintain the small amount of fuel pressure needed for Weber/Mikuni/Solex/Dellorto carbs a return line should not be a problem.

Rob -
I spoke with several folks from racing to engine building to carb work and everybody told me that nobody ran a return fuel line and all were in agreement of 3 PSI - From my research it is better to push the fuel than to pull it with a better fuel flow and more consistant flow. I can push my car as far as I want and there is no stutter - hesitation - stalling of any kind. I was very concerned with vapor locks - hot fuel - low pressure......................so far my set up is dead on. I did not try to overcarb my engine or under power it with my engine modifications. I feel that I have gotten my power band vs hp vs fuel flow about dead on. Planning on hitting the dyno next month - it will be great to see what kind of numbers I am actually putting down.

[Travel'n Man]

Dyno Update

• Rear Wheel Horsepower = 154.11
• Torque = 172.21

http://www.youtube.com/watch?v=Qwf6IbvvQjA

Engine / Mikuni details can be seen in my garage.