The used 250x I picked up ended up needing the cam and rockers replaced due to the last bonehead who owned it running without oil. So now it's back to a stock cam instead of the Web cam it had. So the engine is all back to stock except for a K&N filter and a FMF Q2 muffler & pipe. The carb was jetted by the previous owner to work with the modifications he had done to the engine (which also included a different FMF muffler that was smaller and much louder than the Q2 i put on).

After I got the quad back with the engine all back together, it basically runs like crap. It starts with just a kick or two even in the below-freezing weather we've been having and idles perfectly. It won't rev up though. It spits and sputters like it's choked (and will completely die if the choke is actually on), and this is while sitting in neutral. In gear, it barely pulls 1st gear and just puts around. It actually does better if I remove the air intake tube and let the carb wide open to the air, but still doesn't run as it should. This has led me to believe it's running way too rich, and it does throw out some black smoke when it stumbles, but just a little.

At wide open throttle, it surges up and down like it's hitting a rev limiter, but i dont think it's hitting that high of rpm.

I'm guessing I should go back to stock jetting, or is there another way to adjust the fuel mixture I should check, too?

Could this be a timing issue?

 

the needle needs to be shimed

 

Needle needs to be shimmed... I'm not a cycle mechanic so that doesn't mean much to me. I'm going to try to get the shop that did the work on the phone today and see what they tell me but I doubt they can get it in to fix it right away.

 

I talked to the mechanic/shop that did the work for me. He says he's busy to go anything with it until January, but if I bring in the carb he'll take a look at it (which he didn't check when he had it at the shop. When this work was done, he elected to not replace the cam chain because it looked OK, but now I'm not sure that this might not be a timing problem. Of course, it didn't do this before he had it.

Funny thing is... before he had it, the engine had no oil in it and the cam and rockers were toast and it ran pretty dang good! Now it's back together "as it should be" and it acts like this. The carb apparently had no problems before, but I'm thinking there IS the possibility of the cam timing being off now... simple mistake? He also told me I would never be able to run this quad without it having some problem.. which I think is BS... but he's the only ATV mechanic/shop we've got around here.

Just looking for some ideas.

 

did you try it with ou the airbox lid on? usssally when piped and jetted the lid for the air box isnot used or has a large hole with dust filter,......as far as not being able to run it with out problems I have a 86 250x that i ran for years with no problems till I ran it out of oil lol ...

 

it maybe timeing, but i think your first guess is probably more accurate. it sounds like you need to move the clip 1-2 notches up on the needle. this means takeing the top of the carb off, theres your diaphram, needle and a clip. its difficult to explain, but you will se the needle and above it on the diaphram ther is a clip. move the cilp 1-2 positions up.

this should help your sputtering, also go threw the bottom of the carb and inspect your main jet. if its overly worn or if theres trash in the main it will sputter and have no power at WOT.

try that and take off the air box lid, its probly too rich at idol because the lid is on.
these are things to rule ouf before you go digging into the timeing

 

OK, checked the carb out last night. Everything there looks good...
It doesn't seem to be over-jetted; it's got a 128 on the main and 38 on the pilot.
I didn't see the message about adjusting the clip on the needle so I'll check that out, too. What I did find is a VERY black spark plug with about twice the gap as it should have (.045 as opposed to .025). That would certainly have adverse effects on performance.

Thanks for the tips, guys. I'll update again when I get some of these changes done.

 

ya, i black spark plug is very rich. they may have over gaped it to slow down carbon fouling, because its too rich. if its running way rich like that, skrew your pilot jet in ,after you regap the plug, 1/4 turn IN at a time. then check out your spark plug after idoling a few mins. you want your plug to look slightly brown, like a toasted marshmallow.

when you get to that stage, then i would start working on your higher rpm problems

 

Timing was off. Everything's back in place now and my 250 runs great.

The ***** at the atv shop wouldn't admit he might have set the timing chain wrong and just dismissed my situation as an old POS that would never run right. I've since learned he doesn't give anyone the time of day unless they're into high-performance racing bikes and quads so he can sell them expensive parts.