400ex acting funny/stalling

[kbnorth99]

Hey guys. I had my 06 ex out this weekend and by mid afternoon it was acting funny. It was about 95 degrees (not all that high for my area), we had been riding on and off for a few several hours on trails and hills. My quad seemed like it lost just a tiny bit if power on the low end. a few times it stalled. It would happen when I would be in 2nd at fairly low rpms and I would roll on the throttle to go up a hill. It didn't seem to act different when the rpms were up. When it stalled the engine would let out a low, muffled "thump" almost like a backfire out of the carb but different. During this time when I would start the quad it would knock (sounded like pre-ignition) just as the engine would start. Just one knock.

So it would knock or "thump" when it stalled and it would knock when I would start it.

I had not made any changes really. I did adjust my valves recently. Did I mess that up? I had backed my fuel screw out a quarter turn (it was popping when idling down hill) but I moved that back to the original position prior to this happening (I think my popping is due to a loose slip joint in the exhaust).

'06 400ex, White Bros slip on, K&N, 155 main jet, unknown pilot jet, no engine mods.

Thanks for the help.

[dxcody]

A/F ratio is messed up. This could be caused by your exhaust you were talking about.

[kbnorth99]

Originally posted by dxcody
A/F ratio is messed up. This could be caused by your exhaust you were talking about.

Well then I would assume that it is running lean? The exhaust leak allows too much air flow so there's not enough fuel in the mix?????? So adjust my fuel screw out a quarter turn?

[dxcody]

Thats what it sounds like, try it and see if it helps.

But that doesnt help with your stalling problem.

Im not sure what that is caused by but i have about a 2 inch thick manual for 400ex and when you said you were having troubles with low RPM the first thing it said was A/F, and i am going through some major exhaust leaking problems so it would make since that, that would be your issue.

Let me know and if that doesnt help i will try to help you out with something else.

If i cant help you send a PM to tri5ron, or CJM they are pretty wise and can prolly help you more than i can.

[kbnorth99]

Well I need a new plug anyway so I'll throw one in, adjust that fuel screw out a bit and try my hand at plug reading.

I'll have to start a new thread to see if anyone has ideas on how to repair the slip joint in my exhaust. The previous owner didn't put the proper washers and spacers in the exhaust mounts and the rubber grommets wore out letting the muffler bounce around. It beat that slip joint up pretty badly and now it leaks a bit.

[kbnorth99]

Thanks for the input.