A forum for owners of Yamaha TTR250 trail and enduro bikes!

Jl · Newbie

ttr250 wont run

Aidan · Senior Member

Have u checked the piston?? If it only is only after it warms up it could possibly be oil ( that is now warm) getting into the combustion chamber. Through the rings Or valves. You will notice smoke out the back of the exhaust. But usaly it still runs slightly. Other option is the choke/ cold start is staying open causing the engine to flood with petrol And bogging it out as it warms up.

I'm not sure how to check your cdi, Brian might. But all the wiring diagrams are in the back of the service book on this website somewhere.

Just my 2 cents
Id check the carb first as its much eaisier the play with then getting to the piston( once again u should see smoke if it is the piston)

Good luck!

Lin · Senior Member

There is a 10k ohm suppression resistor inside the connector that joins the HT lead to the sparkplug (sparkplug cap) If this resistor fails the symptoms can be similar to a faulty ignition coil (stopping after 5~10min operation) Remove the cap from the plug. Unscrew the brass ferrule inside with a flatblade screwdriver. Be careful there's a little carbon resistor and a spring that falls out. If you have an ohmmeter measure the resistance. We had one fail and replaced it with a short length of steel (piece of a 4" nail actually) and away the bike went again. It probably played havoc with every TV it went past.

Having checked that out, try a another ignition coil. Ignition coils sometimes work when cold but break down and fail when warmed up. Failing that, try another cdi unit. Yamaha don't publish a cdi test as far as I know.

Cubber · Super Guru

Welcome, Jl, to the TTR forum.

I presume you have checked the breather in the filler cap. confuse

This sounds a classic example of fuel starvation that hapens when the carburettor is starved because air can't get into the petrol tank.

Check the one way valve in the filler cap tube and the tube itself. wink

Martyn

TTRfan · Super Guru

Lin wrote:
There is a 10k ohm suppression resistor inside the connector that joins the HT lead to the sparkplug (sparkplug cap) If this resistor fails the symptoms can be similar to a faulty ignition coil (stopping after 5~10min operation) Remove the cap from the plug. Unscrew the brass ferrule inside with a flatblade screwdriver. Be careful there's a little carbon resistor and a spring that falls out. If you have an ohmmeter measure the resistance. We had one fail and replaced it with a short length of steel (piece of a 4" nail actually) and away the bike went again. It probably played havoc with every TV it went past.

Having checked that out, try a another ignition coil. Ignition coils sometimes work when cold but break down and fail when warmed up. Failing that, try another cdi unit. Yamaha don't publish a cdi test as far as I know.

Excellent information Lin! I was in touch with an owner from India who had replaced CDi, carb, etc and was still having starting problems. Turned out to be this resistor causing the problem.

Brian

Lin · Senior Member

TTRfan wrote:
Lin wrote:
There is a 10k ohm suppression resistor inside the connector that joins the HT lead to the sparkplug (sparkplug cap) If this resistor fails the symptoms can be similar to a faulty ignition coil (stopping after 5~10min operation) Remove the cap from the plug. Unscrew the brass ferrule inside with a flatblade screwdriver. Be careful there's a little carbon resistor and a spring that falls out. If you have an ohmmeter measure the resistance. We had one fail and replaced it with a short length of steel (piece of a 4" nail actually) and away the bike went again. It probably played havoc with every TV it went past.

Having checked that out, try a another ignition coil. Ignition coils sometimes work when cold but break down and fail when warmed up. Failing that, try another cdi unit. Yamaha don't publish a cdi test as far as I know.
Excellent information Lin! I was in touch with an owner from India who had replaced CDi, carb, etc and was still having starting problems. Turned out to be this resistor causing the problem.
Brian

Yes, they can be a tricky little thing.... I've come across two failed resistors - when they fail they adopt a curious grey colour and appear porous.

Jl · Newbie

ok guys i will check everything mentioned. thank you everyone for your ideas. it is greatly appreciated. i will get back to u guys.