1st KTM problem...

Ok. I'm sure this question is vague and that if i searched for 10 hours i might find an answer, but I liek the direct approach, and my first HOUR of searching and reading yeilded little answers and added more confusion.

I just bought a used but great condition 2007 250 XCF-W with a Big Bore Kit. I think the bike sat for the last year mostly. ANyway, initial ride of 5 mins was okay. It had a little bit of gas that the seller left in it (not sure how old the gas was). I put bike in storage for 2 weeks till i could ride again. Then i put new fuel in it (93) and rode it for 15 mins just fine, but suddenly lost all power under any throttle and ALOT of backfiring. Bike idles fine but can't twist throttle without stalling, cutting off, and rapid backfiring. Again, idles like a dream, but acts like it isn't getting enough fuel during throttle. Actually, come to think of it... it even revs fine when in neutral (but will likely still backfire), but it won't run under load (me riding it). Maybe that is helpful to you gurus. VERY bad backfiring, ZERO power. I did see a flame on a backfire.

I ride in the same altitude/climate that the seller is in, so no changes there. Drained the new gas a put in new gas but no fix there. Changed oil and filter just before this happened also (just fyi). Otherwise, I'm a total newb to KTM and to newer dirtbikes in general. My last dirtbike was an XR200 back in the mid 80s.

I'm not too afraid to work on mechanical things, and I have all of the proper drawings, docs and build manuals for this model KTM. However, considering that the bike ran fine for hte first ride and then for the first 15 mins of the 2nd ride, I am inclined to think that the problem isn't severe. Probably something small like a fuel clog or something. ANyway, thought I would ask the pros..... Thanx for reading... Thanx again for answering.

I should add that (according to the seller), the Big BOre Kit is new and has less than 30 minutes on it. So, that and considering it sat for a year, I thought that may be pertinent information. If I think of anything else I'll post it.

Hmmm. I,m thinking electrial. Try a new spark plug, check connections for corrosion or a wire that shorting out against the Frame or something.:thumbsup:

Does it run better with the choke on? If so you could have some dirt or other debris plugging a jet in the carb. Pull bowl and clean main and pilot jets. If you have a lot of fuel varnish and residue in the bowl you may want to have someone go through the carb.

I was gonna say carb or maybe valve?

I had what sounds like a similar problem but not as extreme. My timing jumped on my bike and it actually caused no damage so I reset it and put in a dirt tricks cam chain tightener (A must have honestly) and i set the intake timing off by 1 tooth, it idled and reved like it was mint but didnt have enough power to bring the front wheel off the ground and bogged when hard ont he gas. I figured bad fuel, swapped it out and rode to my buddyes house via the woods, by the time we got htere it was worse and couldnt even get on the gas without it trying to die out.

Might want to check your timing and make sure the marks on the cams line up with eachother at TDC, maybe u have both intake and exhaust off 1 tooth and the previous owner didnt realize which caused him to sell it?

You've got the answer above. Go strait to the main jet and pilot and make sure they are clean. While you are at it make sure the needle and seat are clean. If that doesnt fix it I'm guessing jumped timing and the new tensioner is a must while you are at it. I guess I just repeated what was said but I am bored here at work.

Thank you for the replies. I kinda figured that a simple plan of action would be 1) change spark plug 2) check/clean fuel valve at tank 3) check/clean lines 4) check electrical readings at throttle sensor and lastly 5) clean carb/jet/needle. Do you think it defintiely sounds like carb though? If so, maybe I need to start there first and save time. I know the bike is good overall. When I first test rode it at the guys house (and he seems like an honest guy), it ran strong with no problems. Maybe ran it for 5 mins tops. He delivered the bike the following weekend to my house and I rode it may 10 mins. Again, strong with only 1 or 2 backfires this time though. Then I decided to take it to a buddy's land to put it through the real testing. Stopped along the way and fillled it up with 93 octane (which is the first gas I have added to the bike since receiving it) Ran if for 15 mins and it started with a backfire here and there and got progressively worse over the next few minutes to where any throttle at all was creating more and more backfire (had a machine-gun sound to it) and then it got so bad that you just couldn't run the bike at all (but yet it will sit there and idle just fine). Changed gas, no improvement. Didn't have any time to fiddle with it then, so I'm trying to research so my saturday is as productive as possible. Definitely didn't just plop $3500 on this bike to be wrenching on it or have it sit in the garage broken!

Just thought of something else..... SInce the last thing this bike got was a big-bore kit and then sat for a year, would the needle or main jets (or anythign else for that matter) need to be adjusted for the larger displacement? I would ASSUME that the installer did this since the seller had it "professionally" done, but who knows? Of course, that still doesn't explain whi it rode fine for the first 20 mins....

My 280 has a175 main and a 42 pilot. Stock jetting.:thumbsup:

Pull the carb and go through it. Could be something got stuck in the main, doubt the pilot is plugged as it wouldn't idle worth sh_t. You need to get in there and check.

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