Helping out a friends young son trying to get his 4 wheeler back running again.

He rebuilt the carb initially from an ebay kit and he threw all the original parts away and never could get it running.

I bought this carb for him off Amazon. we put it on and it fired right up. Runs great, no excessive gas smell in exhaust.

Run it for a while, kill it and have a carbon fouled black plug. NO START TIL WE CLEAN IT,

runs smooth as silk with a clean plug. can i just adjust the air fuel screw? Screw is out 2 turns now. I ***-u-me turn in to lean it out?

If that doesn't work I guess I have to adjust the needle that drops down into the carb throat via the throttle cable. Suggestions on a good starting point?

I believe it was 2 from the top on the old carb.

If that doesn't work, I guess I'll have to do a rejet? If I have to rejet I live at sea level by New Orleans.

I need the yamaha part number as well as the stock jet size(S) please? We do not have the original carb.

Thanx in advance,

-=Fred=-

 

First things first, is the choke working properly, if it is slightly on all the time you get a rich mixture, dito a dirty air filter. The adjuster screw is for idle mixture so is your problem confined to idle, or when it is being run normally? If the latter, more likely to be the main jet. On some bikes you can drop the needle via different circlip grooves, on some you can't. The needle one groove further into the jet and see how you go, would be a good start. If idle mixture is the problem, screw in to weaken, this should result in a higher idle, but go too weak and idle speed drops again, so there is a sweet spot. This should be done with engine warm.

 

Played with it last night have the air screw so it's now at 1 turn appox. the plug is looking normal.

Hava a brand new air filter and the choke seems to work perfect idle and mid-range are great now.

but It's stumbling at high speed... so I told reece to go have fun and DON"T rawhide it and we'll work toward

getting the high speed circuit worked out when I have time.

Suggestions?

Thanx in advance

-=Fred=-

 

It may settle down, and are you sure you were not hitting the rev limiter? If it doesn't improve, take a look at the plug after a good long ride, black nose and you need to drop that needle a notch, white and glazed, you need to lift it. You may need to adjust the idle screw again after this.