idle problems

[bigaaron]

Hi! Ok, I got a 2003 400ex and the carb had fuel sitting in it for a few years. It ran fine on starter fluid, but the float bowl was empty because the float valve was stuck shut.

So I disassembled the carb completely and put it in chem-dip for an hour or so. I carefully cleaned all the jets and made sure all the fuel passages in the carb were not blocked. I put it on the engine and it started and ran, but only when I set the idle very high or held the throttle open more then about 10%. I took it back out and checked everything again, and everything is perfect. I adjusted the idle mixture screw out and in to see if that was the problem, no dice. It doesn't look to have any intake leaks or other problems, it just doesn't seem to get any fuel at idle.

What could be the problem? I did the same exact job on the 2003 xr250r I bought at the same time (which had the same green fuel crap inside) and it ran purrrrrrrfect afterwords.

[leasureryan]

try puuting in the next size larger pilot jet, and turning air screw out a couple turns

[bigaaron]

I did get it running yesterday! I figured I would go ahead and try the choke removal mod with a #42 pilot jet. I noticed that the new #42 jet I got was about 1/8" longer then the old #38 one I took out, but the new longer one looks to be the right part.

I put it back on the engine with the idle mixture screw adjusted at 2.5 turns out, hit the starter, and it fired right up and idled as good as I could ever ask for! I don't know what else it could have been though, because the original #38 pilot jet doesn't look to be clogged at all. I hate to mod things in order to fix something that should work as stock, but in this case I'll take it any way I can get it! lol

It does have a UNI filter on it, but stock exhaust. Is that enough to have caused the idle problem with the #38 pilot jet?

[GPracer2500]

Originally posted by bigaaron
....It does have a UNI filter on it, but stock exhaust. Is that enough to have caused the idle problem with the #38 pilot jet?

No. It should definitely be able to idle with the stock pilot jet.

Your symptoms were exactly what happens when the pilot circuit has a blockage. If I was a gambling man, I'd bet the process of removing the choke and installing a new pilot jet dislodged some previously missed blockage. Did you use compressed air? I've found that really helps with badly gummed carbs since the pilot circuit has some of the tiniest passages in the carb.

If you really wanted to know for sure, I'd make doubly sure the 38 is perfectly clean and reinstall it. If, after adjusting the fuel screw and idle screw, it idles then you'd know a blockage was the trouble.

$0.02



BTW, the shorter pilot jet (a series 26) is the correct one. The longer ones are series 21 style pilots. But the 21's are way more common and will work fine in the 400EX carb. The only difference is the length between the slotted end and the threads. Since the EX carb has enough clearance, there's no good reason I'm aware of to bother getting a series 26 if you've already got a series 21.

[bigaaron]

Thanks for the reply, I do agree with you. I just figured that since I already had the carb out I would try the choke removal, and a new pilot jet couldn't hurt since that was the circuit in the carb that seemed to have the problem. After I installed it and it was running, I did also spray some carb cleaner around the carb outlet to check for air leaks but it didn't have any leak at all. It's weird, but I really didn't do anything at all but screw in the new pilot jet and put the carb back on the engine.