I just bought a 1989 lt250r and the spark plug only sparks half the time,and i've tried different
plugs and the same thing happens,it runs but when you rev the engine it bogs down and dies,It will run for a while but when it warms up it will bog and die and it won't start again and if you let it cool down you can start it again and it will do the same thing

 

Sounds like you need a carburator adjustment.Find your air/fuel mixture screw on the carb and turn it half way one way while the engine is running if that doesn't help turn it the other way.That should help.Thats all I know.

 

take the bowl off the carb and clean the main and idile jets in the carb also check the air filer the bike might not be getting enough air

 

It is not anything with the carb. We cleaned the carb and it keeps on doing the same thing.

 

It could be your coil or plug wire

 

Tell u guys what i am having the same problem, but first thing is first my 250 will bog down on top end and sputter so i took it to my cycle shop and they rebulit the carb, got it back still did the same thing so we took it up there again and they thought it had to be the coil it was fine, but when he checked the reeds they were shot so check your reeds then when he checked the piston it was cracked and the rings were shot so we are getting it rebulit and bored, if anything check the reeds, first then if it isnt the reeds then u are going to have check the rings and piston, i hope i was some help

mark
lt250r

 

I think it my cdi,we tested everything else and its fine

 

Plug wires are the #1 cause of the problem you describe. The reason is, if a wire is broken down it only runs worse at high RPM and heat. As the wire gets hot, it breaks down more, allowing the spark to escape and the more RPM, the more sparks and the hotter the sparks. Look at the wire while it runs in pitch dark. You'll see what I mean.

I hope that's your problem instead of others like reed valves, piston rings or cracked piston.