Anyone running a Mikuni, weber or dellerto in a 12a..I have a Mikuni 44PHH setup. It was sold with settings for stockports and headers. My question: What direction do you want to go when running a bridgeport 12a in terms of Main Fuel Jets, Airjets, pilot jets, aceleration nozzles, inner and outer venturi's.



I dO know the general effect of main jets and airjets do to the mixture, but am less sure of the venturi situation with the inner and outer's.



I'd like to get the overall picture before I buy too many "very expensive" Mikuni parts playing around what jet combo's work best.

 

I am in the process of jetting in my 48 DCO on my SP 13B. What I found after the porting was that I needed to go richer on the middle and top end. larger mains, smaller airs, larger accel jets, and a larger choke. I'm sure the larger choke also made me go richer in the jetting, but now the motor will pull in the higher rpm's.



You may want to read this. It may help you.

http://www.mazspeed.com/carburetorfacts.htm

 

Thanks Midget, that carb info page was good. It seems to concentrate more on webers then anything else. I wish i could get a straight answer on the Venturi sizing with a Mikuni 44PHH to see if it helps to enlarge from the 39mm one though.



The site shows that going to a larger one can hurt velocity through the larger you go but no one had changed to a larger venturi's with Mikuni's.



I really can't just go out and by a 51mm Weber, I don't have that kind of money and selling mine through thepartstrader will take for ever to get somewere near the right amount I need.

 

You can run with the 39 chokes in there, but you may not have all the top end that the motor can give. You will have a nice lowend response. I'm not sure how large they go in the Mikuni carb, but I'd try about a 42mm with that porting.



If I were you, Id slap it on the way it is and go from there. You may be closer than you think.

 

Yeap, I do have lots of midrange(3500-5000)power with completely stock setting of the Mikuni. I have experimented with smaller air jets and larger fuel jets in different combo's. Nothing made as much more as stock jetting. I adjusted the fuel pressure down slightly and that helped too? However when you rev this engine really quick like in first gear, it will hesitate at full throttle above 5000rpm momentary, then it takes off right past 8500rpm. IF you let off the gas a little and then floor it while going wide open in 1st at high rpm it works fine. I am not sure if the carb just can't keep up when the engines is accerating very quick.

 

what year is the carb? maybe you just need to work with the bowl or the floats inside. have you had it apart yet? it sounds like it just needs a little love.we had the same problems with my buddies mikuni .it turned out that after a bit oof TLC she run mint. during the rebuild we saw that the bowl was full of gunk.we cleaned her up and shes as good as new.

 

THeres no problem as such, I clean the carb out regularily when ever I take the engine out or when the car has been sitting for over a month without stablizer in the gas. If there was a clogged jet or anything was gunked up interfering with the proper flow of fuel, I'd know it right away, its just the carb is undersized pretty much.

 

It sounds like you may be leaning out at the higher rpm's. That is why it works better if you let off for a while and then get back on it. You could try a larger needle and seat (fuel inlet) to help keep the float level from dropping under hard acceleration, or on Webers you would use a smaller air corection jet to help richen up the high end - not sure what/if they use the same kind of jet on a Mikkuni

 

ya, I thought that too, but when I tried small air jets which will richen the higher rpm mixture, it made less power. so that isn't a problem. The carb is certainly set up for the correct fuel ratio across the board, i am sure of it.