Triple Mikuni thread

[madkaw]

Well I am still playing with jetting, which is fun until you start messing with the accelerator pump settings on the rod-PITA

I have had best results by jacking up the car and working from underneath-still a PITA

I have found the ultimate tool when messing with these carbs, the FORCEPS. Go get some cheap ones from Harbor freight and never drop anything again.

I did do something different today, i ran without my cold air box. I have started from day one with it, so I have never experienced the Mikuni's non-muffled! The cold air box does quiet down the induction noise considerably, and I found that out today. I can see the lure of these triples with just filters, very nice sound!!

[bpilati]

This might be old news to those of you that play on Hybridz, but I , or should I say Todd, figured out my issue. My CAI box backing plate was covering up the float bowl vents, so it was cutting off the fuel to the carbs.

I drove her today and she drove alright. My jetting is still off.

Right now I have

200 main air jet

60's pilots

140 mains

When my O2 sensor was working it showed

14.5 at cruise and sounded great

13+ at idle, but the O2 sensor is more erratic at idle

WOT I was 16+-waaayyy to lean

On the horn with Todd now.

Pic of my CAI that is almost finished except for a good polish. Todd very much liked the CAI and it's got him thinking

Very interesting use of a valve cover.

[madkaw]

Well in Indiana we had a big weather change- cooled off dramatically and humidity dropped off.

So I'm expecting a change in my AFR's to reflect this, but I didn't expect to go pig rich. So I'm figuring I have something wrong- maybe a stuck float ? This is based on the assumption that I am correct on air density in relation to fuel/air mixtures. I am also assuming any single issue with one carb will drive the AFR's askew.

[madkaw]

Fresh from the school of hard knocks, I can tell some stories.

I kind of left this thread hanging as I was writing on this forum and Hybridz.

As far as the suden rich issue, I have had several occasions. It was operator error of course. When doing all the jet changes make sure you get things tight.

I guess when I installed my main jets after another change I neglected to get the jet snug enough and it fell off. Yes, the jet worked itself loose enough to actually fall off and into the belly of the accelerator pump.

What I learned from this-GET THINGS TIGHT! But I also learned how seperate these circuits are. My car ran great at idle and cruise, but punch it hard and it ran like poo. You would have attributed this to some other system malfunction because the carbs operated so well in every aspect other then WOT. And I did trouble shoot ignition and anything else, but it was one unmetered emulsion tube sucking unlimited amount of fuel down it's pipe.

Another "running rich" issue. Cylinder 5&6 are running richer then the others-quite a bit actually. All the jets are secure and float adjsutment is dead on-WTF. In fact, the needle assemblies were brand new-I just installed them not too long ago.

I finally got it figured out when the carb flooded out and I limped home. I didn't get the needle assembly tight so fuel was working it's way around the threads of the assembly and dumping fuel into the carb.

As far as tuning, I am still looking for perfection, but not attaining this. I do believe that these carbs like to be tuned on the rich side to run properly-especially for the transition area of tuning-going from pilot to main circuits. The engine sounds better and smoother the richer I tune. The plugs get that nice tan color with a rich setting.

more to come...

[Kennymonster]

Great to see you're still going at it Steve, I've been jetting on the dyno last couple of days after my cam upgrade, still have another session to go. I'm hoping to contribute with my findings in hopes of providing more Mikuni jet reference to you and others.

[madkaw]

Please do! This is a Mikunis thread- not just my thread .

Love to see some dyno stuff with the Mikunis. I am waiting to have my day at the dyno, but ironing out other issues right now.

Edited August 23, 2013 by madkaw

[madkaw]

Had a break thru with the Mikuni's today. I have been tuning on these for a long time and have done well in all areas except the transition zone. It's the zone where the carbs are leaving their pilot jets and moving on to the main jets.

This zone showed up as a very lean spot to the point of stumbling and my O2 gauge showed +18 on the scale.

What I did was actually close some of the holes that were on the bleed pipe inside the emulsion tube-thus making a stronger "suck" on the main jet from the venturi WITHOUT richening WOT. It was kind of a last ditch experiment that I wanted to try before saying "good enough".

Just exciting to find another angle to tuning the triples and getting closer to FI drivability.

[madkaw]

I got to say, when I decide to move on to FI, I will miss these carbs. Yes there is a little fiddling to do, but i'm a fiddlerLOL Once you get these tuned right they are a real joy and VERY streetable. These perform better then my SU's and have the added tunability and power not capable on the SU's.

Don't bother wanting triple carbs unless you are willing to spend money on an O2 sensor(wideband) to do some real tuning. I know for a fact that my carbs run a lean 15-16AFR at cruise in 5th gear. 4th gear is more 14ish ready to pounce into the 13 teens in WOT application. Idle is almost where I want to make it. The car starts easiest with a rich idle-12-13, but the car will idle at 750rpm in the 17-18 range. The o2 sensor will also troubleshoot for the difference between ignition problems and maybe a loose jet;)

My latest find of altering the bleed tubes has made these carbs smooth as FI. My red-loctite filler for the bleed holes did not hold up over the winter fuel emersion. Just one hole opening up on the bleed pipe was felt while driving. The transition hesistaion started again, and I immediately suspected the bleed pipes-and i was right. I need to experiment with solder and filling the little holes in the brass pipes. I might actually go a little further and temp fill a couple more holes to see how things react.

The only thing to make these about perfect is to be able to come up with a closed element filter or an evap system to capture all the fuel fumes that come out of the huge bowl vents. My trick of turning off the gas and running the bowls dry BEFORE entering my garage cuts down on 90% of the fumes.

Soon will by dyno time. I need to play with my timing some more. I'm going to butt tune for best power and then take it to the dyno. i'm running a fairly aggressive timing now, but might be able to step up a bit. The timing will be nice for off throttle and cruise conditions also. Shooting for about 50 degrees advance during cruise! Should be able to get some serious MPG at that rate.

Thinking i wouldn't mind a set of 44's or 50's on a L28 with a big cam for fun. feeling pretty confident I could tune it well.

[madkaw]

So after some practice I figured how to solder close some of the bleed holes on the bleed pipe. I tried a lot of configurations , but what seems to work is closing the top 4 holes. The effect is like a smaller main air jet in that the main jet reacts quicker . I tried all the smaller main air jets and it didn't have the same reaction as altering the bleed pipe.

I have also learned that there is no way around the fact that these carbs like to run rich to run best. Yes I could stick a small pilot jet in for a long trip and run 16afr at cruise, but it would bring back the transition bobble.

Best power for me right now is

Pilots -70 about 2 turns

Main air 200

Main jet 150.

This puts the AFRs lower then I like at cruise 13-13.5 - 14 depending on gear and rpm . Taller gearing would help for cruise but then I couldn't break the rear tires loose in second gear by slamming the throttle:)

I would also state that a different cam would have a completely different outcome. My Schneider cam seems to make great power down low- thus the big pilots!

Edited June 13, 2014 by madkaw

[Travel'n Man]

Currently I'm at:

• Main Air - 200
  
• Main Fuel - 145
  
• Pilot - 65
  
• Screws - 2.25
  
• Pump Nozzle - 40
  

Bleed Pipe - T

AFR@1000rpm - 13.5

AFR @ WOT - 13.5

AFR @ 60MPH - even pull - 13

Spark Plug - BPR5ES-11

Good pulling power on low accel and high accel

Slight backfire on decel - 15 to 16 AFR

I've got some 195 airs coming from Italy (just grabbed a set of 185's from Todd also). Trying to reduce the slight backfire on decel first - then raise my AFR a little leaner next. My plugs look dry and gray.......I would like them on the more tan side though.

I bought a set of .45 pump nozzle but my car did not like that at all.

What plugs are you running - I have tried 3 different series so far. Keeping notes on the plug reading along with my jet setting so I can review my best 3 setting - then go to a dyno with my best 3 and lock and load for best performance.

Edited June 14, 2014 by Travel'n Man

[Travel'n Man]

What bleed pipe are you running?

[Travel'n Man]

Here are three charts that I like to refer to:

[ATTACH=CONFIG]72111

Edited June 14, 2014 by Travel'n Man