Total Motorcycle Community Forums

I have a 2000 KX100 that was running perfect until sometime last year. My son was riding it, and it just cut off. He thought it locked up, because it drug the back tire, but it was just because it cut off. It is not locked up. I am just now getting around to trying to figure out what is going on with it. I checked it over briefly last year when it quit on him, and the only thing I noticed was that the spark plug electrode appeared to be melted. I replaced the plug, and it was firing, but still wouldn't start.

It kicks over fine, has spark, is getting fuel, has compression. After kicking several times, it will "spit" or "cough" out the exhaust once, and I noticed with the muffler off that it actually blows a blue/orange flame out the exhaust when it does this. I thought maybe it had jumped time, but the woodruff key in the flywheel is ok. I removed the flywheel to check. Compared to cars, the spark looks a little weak, but I'm not sure how strong the spark is supposed to be on one of these bikes.

I have worked on cars for years, and recently been tinkering with motorcycles, mainly my V-twin, but I know absolutely nothing about 2 strokes. I don't know what to check next.

Anybody have any ideas what may be going on to cause this, or what to check next?

Edit: I said it has compression, it has about 70 PSI. Is this enough?

Thanks in advance,
Tony

I ran into the same problem with my bike for quite a while. You'll need a compression of 120 psi +

took me a while to find that cause mine wouldn't start and I had 90 PSI.... you'll probably need to replace the rings. You can try putting oil into the chamber where the spark plug is as it'll bring the comp back up, but I don't know if that'll work at 70 as its kinda low.

Thanks. This has gotten pushed to the side for now. My son totalled his car, so now I'm trying to get that fixed.

This kid's gonna break me.

I have since taken it apart a little farther, and the piston is a little scuffed too, so I may replace piston, rings, and all at the same time.

From what I'm told you should be replacing the rings every 20 hours and the piston every 50 hours... also, it was recommended to basically change your piston whenever you do your rings to keep everything in top running order.

BirdRacer wrote:Thanks. This has gotten pushed to the side for now. My son totalled his car, so now I'm trying to get that fixed.

This kid's gonna break me.

I have since taken it apart a little farther, and the piston is a little scuffed too, so I may replace piston, rings, and all at the same time.

From your explanation, your kid was probably right when he said it locked up. That's not unusual if you overheat a 2-stroke. The kicker is that once it cools off, everything will move freely again. The piston scuff you noticed is a good clue. I think you're on the right track with the rings. If the temp got to high, they could be warped or cracked.