wont stay running

[jason.ragland]

I have a YFZ450r and it wont stay running. I tried to pull start it and it will start up but as soon as I let off of the gas it dies. The plug is fine and the flot moves. I am at a lost. It was running fine before.

[crayfz]

Check your gas tank vent tube.

[jason.ragland]

The gas vent tube is fine. The carb jets have been cleaned. I am at a lost.

[intruder]

How much time do you have on the engine? Could need a valve job or adjustment.

[jason.ragland]

The engine only about 10 hours. I had a chain come off and it put a hole in the case so I took it in and had the dealership put new engine case on. That was about 10 hours ago. But the total time on the bike is about 20hours

[intruder]

what year is it?

[jason.ragland]

It is a 2006

[crayfz]

It might have a prioblem with the electrical system, it makes it seem like it's a fuel issue some time.
Look for a bare wire.
I've had problems up front, around the shock towers,
and beside the battery, there is alittle connection that rusted, it's sort of hidden.

[jason.ragland]

Took the spark plug out and grounded it out. It has a good spark. But I will keep on looking for some bear wires. See what happens when they put to much electronics on a atv.,

[crayfz]

Can't have elec. start without electronics, got to take the good with the bad.

[Jason216]

hey i read your question and the m way it sounds is that you should do a compression check and a leakdown test sounds like it has a loss of compression because if you have to pull it to start it it builds the compression up but there isn't enough compression to keep it running on its own also do a leakdown test you could have a seal of gasket out or even a bad sealing valve with a leakdown teser you should have no more than 10 percent leakdown on your engine. you can also check the carb make sure that it is getting fuel to the intake that can easly be checked by cranking it for a bit and seeing if the plug is wet
good luck let me know what you find out Jason

[jason.ragland]

I will do the compression check tomorrow. I will see what the right compression is. Thanks

[2muchquad]

This is funny,i have seen this 2 or 3 times now.Chances are the cam towers are TOO TIGHT.Whoever put the motor back together probably just tightened the cam towers by hand without torquing them to spec.It will only run if you keep "feathering" the throttle but as soon as you let off it stops as if it "locked up".This sound like your symptoms?:) Just a hair too tight and it can cause problems once the flimsy aluminum caps heat up.