KA24de Mikuni Jetting recomendations

[duke]

So I have been kinda stumbling around in the dark trying to get my Mikuni 44's tuned right. The main problems that I am experiencing is a slight knock under load at low the medium throttle, and a stumble while going from the pilot circuit to the main circuit quickly (ie, stepping on the throttle hard).

Here are my current Jets:
65 pilots
180 airs
160 mains
50 pump jets

I don't know the venturi size, but I expect that it is whatever comes standard. I currently do not have air horns on them, but that is one of my next purchases. I haven't had a chance to hook it up to a wideband O2 sensor yet, but I'm planning on doing that soon as well. I'm just hoping to get in the ballpark so I can dial it in with the wideband. Any help would be greatly appreciated.

[rnorrish]

i'll try to check what on the LZ24 ice racer at home this weekend...
should be close!

i mean if an SR20 is close to a U20 using SUs...
Mikunis can't be that far off! haha!

[duke]

That would be awesome Rich! All I really need is a ballpark. I talked to Rebello today and they said the first thing to do it to soft mount the carbs, so I have a soft mount kit on the way. I'm thinking my first step will be to fatten up the pilot and main jets, and then go from there.

[rnorrish]

try to figure out the venturis, it makes a big difference.

[duke]

From the equations that I have found, it looks like I need the biggest venturi that I can get, which would be 41mm. I'm still a definite novice at tuning these, so any help/advice from anybody would be greatly appreciated.

[okayfine]

From the equations that I have found, it looks like I need the biggest venturi that I can get, which would be 41mm. I'm still a definite novice at tuning these, so any help/advice from anybody would be greatly appreciated.

Duke, I've nothing directly applicable as I've never run Mikunis (or Webers, for that matter). However, when I was playing with ITBs on the KA, the 46mm versions gave noticably less torque than the 42mm versions (despite the ID of the EFI intake being ~50mm), and there was probably something still left to gain low down if I'd have tested the 38mm ITBs. I have a dyno sheet from only the 42mm ITBs and stock cams, but it shows power still rising at 6500 EFI redline.

Your 41mm might be a very good fit and could probably utilize bumpier cams and a bit higher redline. The extra 1000rpm offered by the SR over the stock KA make for a different driving experience.

[duke]

Thanks for the thoughts Julian. I'm not sure if I'm going to go to bigger venturi's or not. We will see.

I did just have some interesting and enlightening experience. My dad borrowed an Innovate LM-1 from a friend, so I figured I would hook it up for shits and giggles to see what was what. Well, my suspected lean condition wasn't there, instead the motor is running a little rich through out the rpm range. It was cool to be able to watch the AFR during a pull. The numbers that it was giving me were low 13's at idle and cruise, dropping to the mid 11's at full throttle pulls. I have also been having trouble with a stumble when you mash to hard on the gas. You could see this also as a quick lean spike up to around 17. I'm thinking that I may need new accelerator pump diaphragms, so that may be my next purchase.

All in all it is a very cool tool, and really informative when it comes to tuning carbs.

Oh yeah, and Rich, I am still interested in what jets (and venturi's) you are running in the ice racer, just for some food for thought.

[defdes]

You can change the setting on the pump circuit by pinning the linkage into a different hole on the bottom of the carbs, tho you probably know that. You could also go up to a 55-60 on the pump jet. Some race ready L16's run up to a 65.
I have the same issue with mine, Mikuni's are not really good under "stomp" conditions, and too rich and too lean both have very similar response.