400EX problem!!

[liverebel]

I have a 2007 400ex with hot cams 440 kit and Big gun exhaust. It has been running GREAT, I mean a real power house. I stored it and I run it about once every other week and have never had issues. I recently tried to crank it and it would not start for anything! So I had my wife pull me off with another 4 wheeler and it start easily. It runs great until you hit it wide open and then it immediately stutters and pop and backfires. So I took the carb apart and cleaned it and while doing so noticed a valve cover stud was broken and there was a EXTREMELY slight amount of oil trace around it(barely noticeable). I ordered a new stud and gasket to replace it with and in the mean time thought this should not keep it from firing. I cleaned the air filter, replaced the gas with race gas, replaced the plug and it still does the same thing! I removed the new spark plug and (im not absolutely sure) it appears there is oil on my plug!!!! Where do I go from here? Also I recently checked the oil and noticed it was slightly over the full mark and drained some to get it a little below the top dot.

[CJM]

Oil on these things is kinda not a huge deal if its slightly overfull since it draws from the oil tank.

It sounds to me like your carbs dirty as well as the valves possibly needing to be adjusted.

Oil could also be bypassing the rings if everything is worn. Compression test, absolute minimum is 100psi. Could also be valve seals leaking, which is quite common.

I would also verify your timing, timing chain and tensioner are all good.

Also, what jets are in the carb now?

[liverebel]

170/38 and it ran like a BEAST on that 2-3 weeks ago

[liverebel]

MAybe poping the head stud caused lose of compression and for it to run bad?

[liverebel]

What adapter do I need to compression test it? M12?

[CJM]

170 is awfully lean brother, you possibly coulda cooked the topend. I was at 170 with a 416.

[liverebel]

PLug was blackened when I took it out the other day. Compression tested just now at 175

[CJM]

Plenty of compression.

Id try swapping to a 180 main.

[liverebel]

Ya it just baffles me that it was running SOO well

[CJM]

Id tend to agree. Sometimes it doesnt make sense either.

[DragonGunner]

Well with jetting it depends more how much compression and how much air your letting into the airbox, more than how much more cc's . So jetting may not be the problem at all sense it had been running great....unless there was a big weather change in air temperture, however with warmer weather you usually go leaner on the main jet. You say you think plug has oil....black, or oily? Or black from running rich then getting gas on it making it look that way....check closely. Racing gas makes it harder to start also. Sounds kinda like a dirty filter, but if you cleaned it then try going back to the carb...did you take the air mixture screw out and shoot some carb cleaner in there...? Put back in at the sae turns out, and try a little at a time turning it out and see how that does. You did clean the carb and jest with carb cleaner right? This is where I would start

[JOHNDOE83]

You Need bigger jetts regardless, you have a 440 now.

170/38 is way to small, theres stock bore exs on here that run 200 size main jets.

My 440 runs a 220 and a 50 pilot, 220 is still lean sometimes for me. But like draggon said, more air flow is a factor in my case.

The only thing I have to say about being to rich in a air cooled for stroke is, it will never be to rich until it wont rev out and sputter/stutter at wide open throttle.

Only then there is to much fuel.

My 440 ran fine with a 148/38, but I never knew it was as fast as it is until I jetted it properly, I blew gaskets and my headers glowed red in the dark.

After jetting, it ran cool and FAST!

www.jetsrus.com The FAQ section is awesome there.

[JOHNDOE83]

Try to post a pic of your plug?

We can determine if its oil or just carbon, if your atv idles then you shut it off, Theres gonna be some black carbon build up.

[liverebel]

Completely disassembled the carb and cleaned it thoroughly. Change gas for race gas to try and get it to fire...the starter seems like after the motor turns a few times and doesn't fire that its logging down the starter. So I hooked to a battery charger and it does the same thing even with 12.9v. Turns a few times then kinda
Feels like its getting harder to turn over.

[liverebel]

http://m.youtube.com/watch?v=nVpV4zBKYrA


Video should be live soon....so I fiddled around with several jet combos and after 2 hours i put the original ones I had in back in...and it started XD so it still is running kinda crappy and I don't know where to go fr
Here. Notice the weird sound it makes when trying to start....sounds a little too effortless but with 175 compression I don't see how it can be that.