won't stay running

[Old Head]

Well my sons 400 sat for about a month. It ran fine before. I got a new battery for it and now it won't stay running. Found so crud in the bowl. I completely cleaned the carb and still the same problem. It will only run at 1/4 throttle with choke on. And half throttle with choke off. If you let off it backfires through carb and exhaust. Sounds like its being starved for fuel to me. All passages are clean and all jets are clean. Any thoughts?:confused:

[RoadRage77]

sounds like your jets ... Check your main jet, if the bowl had crud in it, most likey your jet down too. If it still pops then your gonna have to up the size of your main jet. As it gets colder out you have to adjust your carb.

[Old Head]

like I said it has ran fine for years until it sat for that month. Now it won't run.

[rocky_mtn_honda]

Pilot circuit issues....reclean carb paying special attantion to the pilot/slow jet. Pilots or slow jets usually help if the engine backfires when you let off the throttle. Even if no backfiring is present the pilot (slow) jet may be too lean. The pilot (slow) jet is one of the most commonly overlooked jet in the carburetor. If the engine needs the choke for a long time in cold weather a larger pilot or slow jet will help. If unable to obtain a smooth idle with the mixture screw going up a size or two in pilot (slow) jet will help.

[J.J.]

check the plug.. my dads did the same thing after sittin.. somehow water got in the plug.. changed the plug and everything was all kosher..

if it won't start after the plug, pull start it once and you'll be good to go from there..