xt250 problem and solution

hello everyone. I wanted to post a recent experience so others that might run into the same problem won't pull too much of there hair out trying to figure out the solution. I have an 1981 xt250. I replaced the stock airfilter and box with a unifilter, put a megacycle cam in it with r and d valve springs. New exhaust valve+ valve job, and bored and honed for a 0.5 piston (found a good amount of corrosion on the cylinder wall). After all that buttoned up the engine and it fired right up. It was running a little lean so I ordered some new main jets to tune it up. After finding the right set up it ran great for about a day. The motor started to hesitate and missfire at 3/4 to full throttle really bad. I could hit the redline if I stayed under that throttle position, but as soon as I opened it up it had nothin.

Sounds like main jet circuit to me, or perhaps plug/ignition. I'd check main circuit first, as it is easier. Sounds like you need more gas with all of your mods, or the system can't refill the float bowl fast enough: plugged vent, restricted fuel petcock, other. If you put a timing light on it, and ride down the block at night, you can see it if the spark is cutting out by the way the light flashes. Shade tree method, but it works. If it is: points, coil wire, coil, ignition in that order.

Maybe others have a better idea.

Sorry it took me awhile to post the rest of the story, but stuff came up. anywho... I started to think I had jetted it all wrong and it was probably best to start from square one, so I rejetted it back to the stock settings. It was still doing the same thing, except a little worst! I was starting to get pissed off because it looked like a carb issue, smelled like a carb issue, but no matter what I did to try to tune it, it still was running like crud. My neighbor who works on custom harley builds (is also a mechanic by trade) came over and first thing he said was that it was a carb issue. So, I rebuilt the thing again and no improvement. I was checking the spark plug frequently trying to get a better idea of what was happening inside the motor, and found I had a red plug. I had never seen that before, and after researching it the only explanation I got was because of fuel additives and the plug is fine. WRONG!!:smirk: my new motto: when in doubt... change out the plug! I didn't have any spares on me, and I didn't realize the plug was actually bad yet, so after I purchased 3 new ones, I was preparing to do a plug chop. Since I had 3, I figured I'd throw a new on in there to start, and change it for another one after the motor was warmed up and I had enough road to hold the throttle open for a while. The darn thing started up and ran great! The hesitation and missfiring all dissapeared! so all in all, I hope my experience with this will help someone else out that is running into this type of situation. It may not always be what you think it is, so check every little thing!

Did the same thing years ago (1978) with a DT3, overhauled the engine because I couldn't believe that an entire box of NGK plugs were bad. They were.

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