250sx dies when warm

[Nubbinz]

So for a while my 250sx runs perfectly on a cold start, and for 20 minutes after. Then it first starts to backfire hard, and eventually just dies. I changed the spark plug, cleaned my plastic gas tank out, cleaned the strainer and filled it up with 93 octane, and played with the carb mix. Didn't change a thing. I'm now starting to lean towards the coil being bad, or some of the wiring. I also discovered today the battery has been leaking acid BAD. The paint got eaten off the swing arm and drive shaft tube, and those spots are rusted now. Gonna sand and paint that this weekend. Was wondering if anyone has any other ideas of what might be the problem. I rebuilt the carb and replaced the air filter maybe 4 months ago.

[dougspcs]

Have you checked for spark after it heats up and quits? Is this why you think coil?

Does it restart immediately or do you have to wait for a period of time before it'll restart?

[Flyingw]

When it dies, will it start back up after a few minutes? When it starts to backfire, take the gas cap off and see if that fixes it. One of mine had the same symptoms once. Turned out to be a corroded cap vent.

[Cornholio]

Cdi box, Or the splash shield in the carb is missing and its loading up. My best guess, Had that problem with a 200x, put the splashshield back in and changed the cdi then it ran fine.

[atc500x]

Did you check the valve clearance?

[Nubbinz]

Once it does die, It wont start back up for half an hour, and even then its hard to keep running. Not sure what the splash shield is in a carb but I put every part back in as it should be with all original jets cleaned out. I just bought a multimeter, how many ohms should the coil read, and what else should I look for in other components?

[Nubbinz]

Also, I have not checked valves but normally wouldn't that show up immediately and not take 20 minutes?

[Flyingw]

Did you try taking the gas cap off when it dies? It sure sounds like a tank vent problem.

[tri again]

Maybe the ol' hairdryer trick?
When you KNOW it will start, like when it's cold, hit the cdi with hairdryer and try it.
If it starts, hit the coil with heat and so on.

Compressed air should cool components enough to see if they come back to life.

[Nubbinz]

It has a Clarke plastic gas tank, with a plastic cap. I did blow through the hose on the cap and it seemed pretty free flowing, but I can try running it with no cap next time it acts up. And Ive never heard of the hair dryer trick, I will have to try that. Sounds easier than finding out proper values and trying to use a multimeter.

[atc500x]

start with the easiest,check your valve adjustement,anyway,if you never adjust them,they need to be done