Hey there, first post, i have a 1998 kx250 2 stroke, runs good until you get approx 3/4 into the throttle under a load and it starts running rough, cutting out. I had a preblem a little while ago with the plug wire and had to cut a little off of it but it fixed it. I ran it down the road yesterday and it started doing this. I went ahead and ordered a coil off ebay because thats what it feels like but how would i test the other modules on the bike? Its got good fuel with good premix, air filter is good, plug is new, and the topend isnt that old. Please help, im a fully certified ford tech that doesnt know diddly about 2 stroke bikes lol...

 

Welcome to KF.

So you did a plug chop and determined that you are getting good fuel at that rpm?

Could be a bad wire, cap or magneto in the extreme case. Good luck on the find.

 

well the reason i chopped the wire was because i had a no start problem and i found out that the end came off the wire so i got that fixed and it ran fine for a few days, when it started doing this the first thing i did was make sure the wire had good contact with the end. The plug has good spark. How would i determine that its getting enough fuel at the rpm when its cutting out? The fuel is 91 octane with motul premix and 32:1

 

I meant doing a plug read immediately after a run.

I think it was a good call on trimming back the wire for testing. Now that you have proved that you have a wire issue I would prefer to install a new wire and boot since the boot and wire are deteriorated.

 

I think on this bike the coil is attatched to the wire, like made together. Is there a process to splice a new wire on?

 

You are correct. After looking your parts up in the fiche, coil is p/n: 21121-1281 with wire, and the plug cap is 21130-1073. The clamp is 92037-1173 and looks like a zip tie. You would think that you could be able to just add a plug wire somehow, but I have not worked on too many newer dirt rides.

edit: looks like 7mm spark distance is the norm it seems when testing the coil and wire.

 

Check Powervalve? Exhaust leak? i had a 97 Kx125 that did the same thing rebuilt the powervalve...huh i couldnt keep the front fender outta the clouds.....

 

hahaha, I need a manual for this thing now. lol good point on checking the exhaust valve. (Inspect after every 3 races per the 88 manual) A compression check may be in order as well. (noted this after reading up in my 88 manual of possible carbon buildup)

I understand that I stated info from the 88 manual and not from the 98 manual, but some mechanical issues/symptoms may occur throughout most bikes. Just more food for thought stuff. lol

 

Here's an update, changed the plug to a lower heat range brs6 series plug just for ****s and giggles out of my powerwashee, runs great through first gear, does the same thing it was doing in second though, which leads me to ask, what gap should I run on the br8eg that I just bought for it, running 32 right now which I read somewhere else on the Internet. Hopefully that's my problem. I will check the powervalve too

 

I see .6-.7mm gap across the board for the NGK BR8EG 125, 250 and 500. So .0275 is tops for the gap in my 88 manual.