Hi - I'm trying to fine tune my carb and right now I'm trying adjust idle speed. My shop manual does poor job of explaining idle adjustments.

A little background: 1994 300 4x4, had a mechanic clean and rebuild carb(with a complete new kit) and although it came back running and no longer leaking, it wasn't running very well, especially at idle (way too low and had to nurse throttle to keep it going).

Based on a lot of reading, i reset idle speed screw to 1.75 turns out (the big thumb screw in middle of carb). By doing this I discovered that he had left this screw waaay out. Although I didn't count, i think it was 5 turns out.

It now runs great, noticably smoother, it'll idle all day, but it's idling WAY too high now. So much so that shifting into gear is hard.

Would really appreciate tip on what adjustments I should try next?

 

What happens when u turn your idle down. Try turning it down. If it wants to stall out check your fuel filter. It maybe partially plugged.

 

Just make sure your air/ fuel mixture is 2 turns out and the thumb throttle has about an 1/8" slack. The big"thumb screw" is just for the idle speed only. If you can't get it to idle down low enough with this screw,at the top of the carb the throttle cable can be adjusted to where you can have more slack. It has a small lock nut you loosen and turn the cable adjuster in for more slack.

 

OPT - thanks i will try this after work tonight. I'm guessing this may be at least part of the problem (don't recall slack). Is there any adjustments or anything that I should also check on other end, up on handle bars?

 

That's the 1/8" slack I mentioned you need at the thumb throttle. Just pull back the rubber cover on the throttle housing and you have a cable adjuster if you need to adjust it.

 

Ok got home and messed with it a bit, think i'm making it worse now (although high idle is gone now). Would you mind clarifiying what the starting (or stock) recomendations are for each of these... how many turns backed out from seated?:

A) the big thumb screw (on side of carb, in middle)

and

B) the small little brass screw that is just left and a little lower than thumb screw

After reading your post and lots of other posts, I'm not sure which one you were referring to when you said:

 

The air/fuel mixture screw is the small screw to the left of the knurled idle adjuster. Just check how many turns to a lightly seated position. Should normally be between 1 1/2 to 2 turns in most cases and usually not as sensitive as a fuel/air(pilot) screw setting on a 4 stroke engine. Just set at 2 turns out and adjust the big knurled screw to where you can get a good idle.There is NO set turns out for this adjuster! Just adjust to a normal idle. Again make sure you have a little slack at the thumb lever.Here's a couple videos on Mikuni carbs similar to yours. Hopefully will help you to understand better on functions of this carb.

 

OPT: just want to say thank you for sticking with me and posting so many great replies. That last post really cleared things up for me and I was able to go back out and got it running really nice (and idling).

I will watch the video links soon now too, but wanted to post back while it was fresh on my mind. thanks!

 

OK, been making progress lately. Have AWD system working properly and overall I can get the carb adjusted so that it runs pretty nice. In fact tonight I thought I had it dialed in perfectly - even idling "perfectly" while I did stuff in the yard, for quite a while. But then I put it in gear and drove around yard a bit, putting it in and out of gear, then parked it and tried to let it idle in neutral again........ BUT then idle was totally different. It idled MUCH higher so much that I couldn't shift it into gear.

Looking for some advice on why doesn't come back to same idle level after using throttle.

Any tips for me?

 

If you're sure the carb slide/cable isn't sticking or dirty,then could possibly be an air leak from air boot,air box crack or could be a leaking crank seal behind the drive clutch,base gasket leak,etc. Air leaks can cause erratic idling,running too lean,hard to adjust the carb,etc. Plus on a 2 stroke always check compression. Top end compression,bottom end compression go hand in hand.