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/B00029JC6M/ref=wms_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/showthread.php?42045-Wolf-Creek-Racing-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.

[ATTACH=CONFIG]52519[/ATTACH]

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/showthread.php?42045-Wolf-Creek-Racing-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)