300 fourtrax help!!!

[jcs327]

I am working on a 300 fourtrax (88) model that idles fine but bogs above 1/8 throttle. fresh rebuild on the carb. 120 main/42 pilot which are stock settings. stock filter & pipe with airbox lid on. spark plug is black soot. seems like its stuck in a real rich setting. I moved the needle clip to the top position and adjusted the fuel screw and no change. I checked everything in the carb for proper assembly. could this be a valve problem causing this, or possily a head gasket?. it idles fine.

thanks in advanced


puzzled.

[yellowzo3]

one of your jets might be wrong...might be your main...also is the gas old? it could be dirty and when your giving it gas it just clogs up...if you can change the spark plug after you try some different things..hope that helps

[jcs327]

new gas. factory jetting. 2 turns out on fuel screw. only thig i can find visibly wrong is a small crack in the airbox boot, but that would normally make it lean out, not run too rich. any suggestions?

[400 SS EX]

Sometimes you can be surprised how dirty yoiur filter is can cause stalling. Try doing running it without the filter for a little in your garage or whatever. Make sure you put in a new plug now or at least clean this one really really good.

[bwamos]

FYI the stock pilot should be a 38. (err.. I could be wrong though if your talking about the utility version)

But, that shouldn't really cause an issue.

You said the needle is in the top slot? Closest to the blunt end? That would be your problem. Put the needle clip in slot 3 w/ the washer above the clip. (Slot 1 being at the blunt end.)

If you are running, a 122 main, stock filter, airbox lid (unpunched), needle in 3rd slot, air screw out 2-1/2 turns, and pilot 38, then you have another problem.

Did the fresh rebuild include a new float valve? Also, jsut to be 100% sure make sure you didn't forget to install the o-ring on the upper slide access cover. It happens. ;)

You are getting a rich reading on the plug, because your idle circuit is too rich. But, as soon as you move the slide it leans out, because the needle is too far down into the needle jet.

[jcs327]

It is the utility version. It currently has a 120 main which came in the stock carb kit, and a 42 pilot, sounds like its out of the normal parameters to me. the o ring you mentioned on the top slide access cover, is it the cover gasket or the diaphragm that is attached to the top of the slide itself?. I will try lowering the needle clip and see what that does. thanks.

[jcs327]

by float valve do you mean the float needle?. I replaced it. I see now what you mean about the idle circuit being too rich. It idles fine though. So, I will try a 38 pilot in addition to the needle clip in 3rd position.