US90 running lean

[Cribbs74]

So my 90 has been running lean since I aquired it. It has a rebuild kit installed. Idles smooth, revs nice in neutral, but chokes out and sputters under load. I have moved the needle to the lowest clip position and while it got better it still cuts in and out. If I run with the choke on it's fine, revs smooth throughout the range and pulls well.

Any Ideas? I don't want to run with the choke on all the time.


Ron

[derrick81787]

I'm in the process of fixing a similar issue on my ATC 110 that was caused by a leaky intake manifold gasket. But I don't know if that's it or not because my situation was kind of the opposite. Idled poorly but did okay when I gave it more gas. You could always spray something around the intake manifold while it's running and check for leaks, though.

Otherwise, maybe you need a larger main jet? I know that 110s are supposed to have either a size 82 or 85 jet. I don't know about 90s.

Edit: I also had a similar issue once due to a bad spark plug. I don't think it was running lean, but it would sputter like that while giving it gas under load. Evidently it was sparking enough to run but not enough to do a good job because I replaced the spark plug and it ran like new again.

[coolpool]

What color is the plug tip? Check for air leaks as stated above. Make sure your float is set correctly and that your fuel is flowing freely from the tank. Is it the same in the "On" and "Reserve" position? Loosen the gas cap and see if that makes a difference. Did you check the screen in the petcock area for crud? Might be a timing advance issue too.

[Cribbs74]

No crud in the screen, same on reserve, plug tip is a bit on the black side. Did not check the float, but will do so when my new bowl arrives.

A bit of info I left out by accident is I am running a DG? Header and muffler. Would that require a re-jetting? I hate the darn thing. Way too loud and I doubt it adds any noticeable hp over stock.

Ron

[coolpool]

Black is good :-) I would be wary on that pipe set up with stock jets, although I'm no expert. Maybe PM shortline10 as he's a very knowledgeable guy when it comes to tuning these things up with aftermarket parts. No sign of the parts yet? I checked the tracking and it says it arrived in a "Foreign Country" lol. Ooooooh, Oklahoma sounds exotic ;-)

[Cribbs74]

I checked timing today and it was way off. After adjustment I got a bit of power back as I am now able to do wheelies, but no change on the lean run.

I'll keep you posted on the parts arrival here in luxurious Oklahoma. Thanks for the help.