Triple Mikuni thread

[madkaw]

Those jumps in jetting sizes are too big. I found with my NA that a full 1.0 add was worth over a point on the AFR's. You might get it with the 155's.

Man I should would like to ride in that 'monster'!!

Don't forget to calibrate your O2 sensor often. You don't have much room for error.

Edited August 15, 2014 by madkaw

[Kennymonster]

Yeah the 160's were an experiment to see how it behaved under super rich condition, under load, that gave me an insight for pilot to main transition under high gear / boost.

Been just informed that Mikuni air jets only come in 10's, not 5 increments??? Bah, I'll try the 155's with both 170/180 airs I guess.

I think my AEM unit does a self calibrating routine at start, or it seems like. Next time you're out here on the West coast, holler and we'll go for a drive!

[madkaw]

If my son goes back there for Nationals at Irvine - I will take you up on that offer.

I noticed that the smaller main air jet richens the final WOT mixture

[Kennymonster]

Got the 155 main / 170 air combo in today, took care of the transition problem for high load @ 3rd / 4th gear

The smaller air corrector seems to have done the trick, mains kick in lot earlier and the 'lean spike' doesn't go past 12, at WOT it's at 11.2 to 11.3 under 4th gear pull to 6000.

Car feels happy with the nice fat mixture.

[madkaw]

Glad you nailed your mixture. It seems these engine like fuel!!

[RyanT67]

Great thread, very informative!

Time for me to join in all this fun...

Just got my wideband (AEM UEGO) up and running, and was pretty shocked at the numbers I was reading...

Warm idle AFR @ 1000RPM - 11.4

4th Gear @ 2000 RPM - 12.5

WOT - 2nd gear @ 6000RPM - 10.5

A little rich, shall we say?

Running 44's on a 3.0 stroker.

Pulling the jets tomorrow to see what I have in there. Had these carbs rebuilt just over a year ago by a reputable shop, so all else should be good.

 

Might as well post an update, as I have been going through a pretty epic struggle with my 44's over the past few months.  I'll post more on all of that later though, as well as a very detailed strip down and rebuild of a Mikuni 44PHH to help others and save them from the potential mistakes I made.  

So, as it stands, I am now running:

 

Pilot:  55 (1.75 turns)

Main air:  200

Main fuel:  150

Outer venturi:  34

Idle:  12.4 afr

3000rpm in 2nd (30mph):  13.0 afr

WOT in 2nd:  10.5 afr

Still running very rich, in spite of running a much larger air jet.  I do have a set of 140's to try though, but I find it a little confusing that others are running 160's and getting much leaner figures...  I also have a set of 37 outer venturis that I will throw on and see what happens with.  

In spite of my AFR's not improving, the car does pull remarkably harder now, and it seems there is still room for more improvement.  Before I had some stumble when flooring it, now I don't.  I also used to have a little stumble in 3rd gear around 5k RPM and it is now gone.  

Best of all though, I can now floor it in 2nd gear at around 30mph, and the rear tires will actually break loose around 4k RPM and not catch until I go to 3rd.  Very addictive!

I also now get 115 miles from 30 litres of gas, whereas I was getting more like 75 miles before.  So I went from about 9.5 mpg to 14 mpg.  This is under spirited driving and city driving, obviously.  I get almost 25 mpg on the highway at 70 mph.  

Winter is now here though, so into storage she goes.  

In Spring I will be trying:

50 and 52.5 pilots

140 fuels

37 outer Venturis

Will probably go ahead and see what the venturi does first, with my current jet set up.  

[CoastGuardZ]

Hey fellas!  Just stumbled upon this thread and the info is outstanding!  Just curious if anyone has continued on with their tuning projects this year?  I'd love to see some updates.

 

Some things I've been curious about recently are how people are fuelling the carbs... where are the lines ran, pressures, distribution blocks, regulators, mounting locations, return vs. no return line... etc. etc.  So I've been scouring the interwebs looking at engine bay pictures. 

 

I picked up my setup as a complete unit that the previous owner was swapping out for a RB25 turbo project.  It ran great when he pulled it out and it ran great, and still runs great, after I dropped it in.  Rebello 3.2L stroker w/ 44's.  I'd did the swap right before moving to Florida in 2013 and since then I have had very little chance to drive or tinker with it.  Between the humidity here in the FL swamps, absolutely horrible drivers and high car theft and vandalism, I only occasionally take it for short cruises... which is killing me slowly.  However, with a change in job and location this summer things should start to free up for me to get back at it

 

The other day I ran into my first starting issue though... she had to cool down after getting fuel... vapor lock I'm thinking?

 

Anyway, thanks for all the time you guys have put into this extremely valuable thread, and as soon as I have something useful to contribute I'll make sure to post.

[madkaw]

I was wondering how that swap was going. I met you at C&C in Indy.

My car started better with a rich idle mixture. My Mikuni's are dead headed at the carbs, no return line. Holley regulator. I think it's all in this thread.

Glad to hear from you. 

[RyanT67]

Still plugging away with this. 

Latest:
Pilot:  60 (1.5 turns)
Main air:  200
Main fuel:  140
Outer venturi:  34

Idle:  13.2 afr
3000rpm in 2nd (30mph):  13.4 afr
WOT in 2nd:  11.5 afr

Going to check my valvetrain tomorrow, and confirm a few other things while I am at it.  Surprised I am still a little rich with 140's for main fuel.  

I have a set of 37 outer venturis I could use.  What effect will switching to them have?  Presumably more air, which might help with the richness issue?  

[Mike]

Hey guys, not sure if you saw this or not, but, I just posted a Mikuni manual from my collection.  Not sure how old this one is, but, check it out.

 

http://www.classiczcars.com/files/file/13-mikuni-manual/

[madkaw]

So my engines apart and I'm wanting to check the carbs over before putting them back on. Since I was having running issues with my engine I really wanted to eliminate the Mikunis as the source. Everything checked out on the carbs, but I was suspicious of throttle plate damage from slamming the throttle(maybe a few times:o)

Looking down the barrels with back lite I tried to eyeball the light making it through and see if the openings were the same. Checked for looseness in the throttle plates also. Some looked suspect, but still not sure how to measure the opening.

Then I had an idea(careful now), what I checked the air balance with the carb off the engine. If I had a consistant suction I could use my unisync to measure any differences. So I dragged out the Oreck( my wife got excited for a second), and I hooked it up to each carb and measured. If this is an accurate test, then my carbs were pretty spot on.

I plan on stteing all my idle screws using the vacuum. At least I will know they are all set equal. never did like using the feeler gauge

[madkaw]

So I finished tweeking the carbs with the Oreck and quick put it back in the closet before she got ideas!

I would suggest a fresh bag in the cleaner before attempting this. I noticed that some of my readings were fluxuating as if the suction was varying. I pulled the bag to see it was very, very full. So I got a new bag and proceeded. I did find one carb that seem to have a tweeked throttle shaft. A few yanks on the opposite throttle plate nuts and she dialed in.

I moved on to slimming down my vacuum log. ive been trying to come up with a way to eliminate the hoses running over my carbs. I think this set-up will work and look much better.