New to the site, just got a 400ex Backfire/sputter 1/4 throttle, not pilot jet

[TL_2ENV]

I just picked up a 02 400ex for my gf, the night i rode it it seemed really cold blooded, not too bad i didnt waste much time with it the price was right so i picked it up

At first it wouldnt idle much on its own for nothing, so i took the carb out, both jets and cleaned them, messed with the idle screw. I finally can get it to idle when its warmed up of course. but at about 1/4 throttle it runs but not consistent. It will go and then stutter, go again. Seems as if its backfiring through the intake. I changed the plug, and did the carb. I was wondering what are the signs of valves needing adjusting? I was going to do it today. I ordered 150/40 jets it has a motoworks slip on, so i figured it wouldnt hurt at all. When it runs passed 1/4 throttle im surprised how much power it seems to have, im coming from a 700 raptor, so im all new to carbs and everything else

If you guys have any ideas how i can get this up and running please let me know thanx

[bigbad400]

sry but it sounds like low compression. maybe it needs a freshening up.

[JOHNDOE83]

www.jetsrus.com has the info on when to jet, your running to lean. also many threads on here about jetting, just search for them.

may need a piston but try the jet first, might be the needle needs to be raised a lil bit.

[jasonwayne222]

mine was doing the same thing after i rebuilt it, not quite at quarter throttle, but when i would cruise and barely give it throttle it would sputter real bad, it ended up being the carb was way out of adjustment, had to move clip on needl, go up on pilot, change main jet and adjust air screw

[TL_2ENV]

got this all fixed went up one spot on the needle, and changed jets to 150/40