YapaKanichi

I was wondering if anyone has the recommended fuel pressure needed for te Mikuni 38. I believe thats it CARL HELP! He knows all this stuff I have horrible memory. Ok I need the fuel pressure for a Mikuni Carb. I have to redo my fuel system basically. HEHEHE bet no one had my fuel system I had oh yea, only for the dangerous.

someone82

I'm running 3 1/2 psi... Fuel system below in signature

matt

YapaKanichi

the 44pph? There's a number inside my stack that says 38....what does that mean?

Rx7carl

Thats the venturi size. 38MM chokes.

YapaKanichi

venturi......man...Carl what does that mean...or what do they do/mean?

Siraniko

iTrader: (13)

For SP motors, no need for venturies. thats how they were originally sold by RR&R.

kuhlrx7

I ran between 5 & 6 lbs when I had a 12a large street port w mukni in my car. the carb was set up with the larger valve though. below 4.5 lbs it would not run right. others have had same experance. stock engines seam to do ok at a lower presure. stock 12a pumps do not seam to keep up with the amount of fuel needed with this type of carb. mukni had 44,45,48 sizes for our cars. may be carl could help you id yours.

Rx7carl

Mel, yank the venturis? Are you serious? What about re jetting?

Man, your guys fuel pressures are all over the place

alien_rx7

Hmm, Mikuni made the PHH model in 40 and 44, possibly a 50 or 51. That is it. They weren't specifically made for our car. They were very popular for the Z cars and other Datsuns and are also seen on BMW 2000/2002, and many VW's. They had the same bolt pattern as the Weber and Dellorto.

The Mikuni PHH 40 comes stock with a 32 venturi but venturi were available all the way up to a 39 for the 40's. They are also run without a return so doesn't that usually mean a low pressure? The size of the PHH Mikuni is inked on the outside of one of the barrels. Mine were faded but still readable. There is a long number and 40PHH in it.

I haven't installed mine yet (dual carb setup) but I wouldn't think that more than 3.5psi would be required but if it is I have the Carter 7psi/100gph(?) fuel pump, would just have to switch out the 1-4 Holley FPR.

Siraniko

iTrader: (13)

Carl,
yes, no venturies at all. for the jets, i will get the specs this weekend. I have Nicks killer-b carb. But I noticed that its only designed for mildly ported engine. My old and newer SP 13-B ran but not enough to make me say OH ****. On the other hand, back in the 80's, Nick built a half-bridge on a SA using mikuni. She (the only female racer back then) was one of the fastest RX at the Stadium Way street racing. Maybe Nick built her a small half-bridge.

Mel

GOOFYROTOR

All mikuni carbs have a tapered barrel it is not a TRUE 44mm. So, no venturies necessary.
however, WEBER carbs are not like that, its a TRUE 40mm,45mm,48mm,51mm,58mm,64mm.

kuhlrx7

alien_rx7 check your data. mikuni made a great number of carbs and sizes. For many uses also. weedwackers to airplanes. between the 70s and 90s mikuni sold a number of differant carb pkgs for rotarys (intake and carb pkgs). for rotarys on intake they had both downdraft and sidedraft styles ( lake city & u shaped I think ) and not just the phh was used. I nowhere implied that They were specifically made for our cars. like many other performance carb manufactures they made several carbs that were used in many aplications, datsuns, bmw,vw, opal ect ect as well as mazdas. in the mid 80s I bought a used setup that was a 48 and used it for 2 years before nick sold me a new 44 side draft street system. the mikuni race system was a 51. did I mention just the phh in my above reply?

quote:
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Originally posted by kuhlrx7
I ran between 5 & 6 lbs when I had a 12a large street port w mukni in my car. the carb was set up with the larger valve though. below 4.5 lbs it would not run right. others have had same experance. stock engines seam to do ok at a lower presure. stock 12a pumps do not seam to keep up with the amount of fuel needed with this type of carb. mukni had 44,45,48 sizes for our cars. may be carl could help you id yours.
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per rr&r trouble shooting booklet sugested fuel pressue is 4 1/2 to 5 lbs. your stock fuel pump is sugested to be replaced with high presure fuel pump and regulator part # rrc 1064 as the stock pump is not able to flow amount needed. jetting as well as fuel presure and altatude should be considered when tuning the carb.


I was told back in the late 80s that mine would most likly run better at a little higher presure due to larger needle I was useing. with the stock fuel pump I would run out of fuel shifting from 2nd to 3rd. I tryed several adjustments to the pressure and found 5-6 lbs to work best for my set up. both of my mikunis used a return system. carl what do you think his fuel pressure should be? I no longer have or use a mukni set up as I went 13bt.

YapaKanichi

what return needle size did you use? 3/8 or 1/2?

kuhlrx7

the return line used a jet before I used the fuel presure regulator. the needles went to a size 2.0 I think. its been a few years ago that I sold my last mikuni set up.

Siraniko

iTrader: (13)

I use a jet on the return (where the flex hose meets the hardline) to at least slow down the flow back to the tank.

alien_rx7

Yes, I do know they made a great number of carbs for a number of different applications. In fact, carbs are still made for bikes IIRC. And no you didn't mention just the PHH, my bad

Though I haven't measured the internal size of the barrel, I tend to agree with Goofyrotor. The inlet size as measure on my 40's is approximately 45mm depending on the accuracy of my calipers so maybe they taper to the 40mm somewhere and then again with the venturi? One of these days I'll purchase the PHH manual

GOOFYROTOR

the mikuni tapers behind the butterflies.
bigger top smaller bottom.
mainly for low end power.

YapaKanichi

so I need to run about 4-6 psi I'm getting at.