Triple Mikuni plumbing questions

[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/Part-Type/Fuel-Distribution-Blocks/Product-Line/Mr-Gasket-T-Style-Fuel-Blocks/?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.

Edited April 3, 2012 by Carl Beck

[madkaw]

So simple I over thinked it!! It just hit me like Mikle Tyson:stupid:. 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:stupid:. 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).

Edited April 3, 2012 by Travel'n Man

[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!