22mm mikuni - rich at high rpm only

[ForceFed86]

So my 212 setup is a basic predator short block with a non hemi head and no HG. 1.3 rockers, 18lb springs and exhaust.

I have a 22mm miki on it. 120 main jet. Im in the middle on the needle. I just put a WB02 o. The bike to see how close I was. Idle is arund 14s, 12.5 through mid rpm range, then up top its dipping into the low 11s. I take it to about 7k. 330ft drag race only deal.

Is there an easy way to lean out the upper range only on the 22mm miki? Its the round slide china version.

 

[ForceFed86]

Pic's

 

[Brianator]

Try a slighty smaller main jet (which is effective from 3/4 - WOT), but I'd first pop in a fresh plug, do a WOT run and hit the kill switch without lifting the throttle. Then when it cools down remove the plug, do a plug chop and see what THAT is telling you. It's still the best way to see what's going on and what professional race engine builders do. Just to be thorough, what model of 22mm do you have? A VM? IF it has a powerjet it may need to be tuned a touch leaner.

*edit* something I just thought of is maybe your air filter isnt up to the task? If its reached it's max airflow the engine will start to run rich.

 

[ForceFed86]

Its a round slide china 22mm with a 4" straight intake on it


Thanks for the tips ill give it a try filter less. I dont quite relate to how the 3/4 throttle stuff relates as Im wide open from start ton finish. So not sure if needle position even matters. I was thinking drop main jet and raise needle to fatten up in the middle? But if in wide open will that even matter?

I Worry that a drop in main jet will lean the mid rpm range out even more, which I dont really want. High rpm tuning is usually an air bleed in the carbs i work with.

 

[Gx200drag]

Hey um, what's that blue bottle u got there next to ur seat???? Lol

 

[ForceFed86]

Lol, Future plan is alky and nitrous with a standard hemi head and gasket to lower compression a bunch. Just working on learning tune up. New to miki carbs

One of the head guys in our group has a slick ethanol powered rig thats basically a stock long block hemi with a 20 shot on e98. Runs great!

 

[Brianator]

Needle controls the mid range (1/4 - 3/4 throttle), a smaller main shouldn't affect it TOO much. Each circuit in the carb (pilot/mid/main) are active within their respective throttle position except for the pilot which actually affects the entire range because it's always spraying fuel. If you're wide open from start to finish you're only using the pilot to idle and bypassing the needle anyways. If you're running rich up top then chances are you're running out of airflow. Read "Spankys jetting guide", even though its geared for 2 strokes it applies to that style of carb and you'll learn alot. I'd still try a smaller main (110 if available) as a test to see what happens on your wideband. Going alky or e98 is going to require a complete retune (way fatter) and ALOT more airflow.

 

[KartFab]

I wouldn't let it idle above 13.2:1 FYI.

Try blipping the throttle to 1/8" open. you will get a better response if you are idling at 12.5-13.2 MAX AFR.

I wouldnt be too worried about the low 11s on gas, but you will get optimal hp around 12.2-12.5 AFR.

Main jet is the only thing you need to replace (go 1 or 2 sizes smaller and test).

Again, id be mroe concerned about throttle response off idle if you are idling at 14:1 its already too lean on the idle circuit and needs adjustment.

 

[bob58o]

Jets are like women....
Fat and happy, or lean and mean. LOL

Interested in following this thread. Put a smaller main jet and repeat this test. Let us know how changing to a jet one size smaller affects the AFR.

Or actually I like tuning from the bottom up. I like to start with the pilot jet / air screw, then needle clip, then main jet. So you might want to start by turning the air screw in a bit, or upping the pilot jet to enrichen the idle mix like KF suggested. OR if happy with how it is when you whack the throttle, just play with the main to lean out the top end. Take notes and only change one thing at a time.

I'm all about testing. Love the data.

 

[ForceFed86]

Appreciate the response! It's a Juggernaut converter setup, I stall it up a ways on the line and the gun it. Its well off the idle circuit at that time. But I will play with it a little and see how it goes! I do notice I basically have to richen up the idle a good half turn with my thumb nail to get to fire over easy when cold. Then I lean it back out until I get a lowish 1500-1600 rpm idle. Once warm it fires right up and idles well. I was pulling fuel to get it to idle where I wanted.

I filled the tank with 91 and threw in 1 small yellow bottle of heet. (straight methanol) This leaned it out to 12.4ish up top. I like having the added octane and alky in there anyway. The compression is pretty high on this little fella with no HG and the non-hemi head.

In all honesty from say 3500-5500ish its a mean mofo! Pulls VERY well. Falls pretty flat after that. After that point adjusting the mixture rich or lean doesn't feel like it does much. May just be out of cam? I had a MOD2 on my last non hemi and it felt the same.

Everyone said it was the stock carb at first, so I replaced that. Didn't seem to make any difference. In fact I'd dare say my stock carb felt better for what ever reason. Maybe I need to hog out the head a bit. I just doubted I was out flowing the stock ports at this power level.

Odd stock carb, cam, clutch guys can pull around me. I was blaming the 40lbs weight difference! Tho I'm only at 210 or so suited up.

Feel like the converters just aren't up for the task... Even this new fancy juggernaut. I had a dual disc cheetah too. Its like it wouldn't engage till after half track (150ft). It was slower than the Hilliard extreme clutch by a ton.