03 yzf450 suddenly wont start

[gordfraser]

Hi everyone,
my yz used to start easy. all the time.

now suddenly it wont start unless you kick it 20-30 times+ and you have the throttle at least half open.
it always used to start like normal with no throttle!

cleaned the carb, checked all the electrics by the book.....

noticed recently that it spitts out coolant from the overflow.
it never did that before.

does that mean head gasket??

or what else?

G

 

[IndyMX]

Have you checked the valve clearance?

 

[gordfraser]

yes, valves are done.

 

[IndyMX]

Done as in used up? As in needing to be replaced?

 

[gordfraser]

they were adjusted just after the problem started.
they were only out a little.

 

[IndyMX]

Well, you should at the very least do a compression test. Better yet a leak down test.

And maybe even a coolant system pressure test.

Non of those will point to a specific problem, but will definitely help diagnose the problem.

 

[gordfraser]

any idea what the copressions should be?

and whats a leak down test?

 

[gordfraser]

ok googled the leak down.
i got my hands on a compression gauge with the car air valve for the leakdown, but i need a 90 elbow tomorrow when the store opens.

are the CDi's troublesome?

when it goes it runs well, but sounds a little bit like the timing is out. everything checks out, but there is an aftermarket stator so i have no timing mark on the crank to setup from.

the piston seems to be at top dead when the cam marks line up.

 

[gordfraser]

the leakdown test showed that the exhaust valves have a small air leak, even at lower pressures. 10psi and even less
Sorry but couldnt work out all the gauges, but we even took the cam off the exhaust side to make sure they should be closed.

there was no leak in the inlet side or anywhere else that we could tell.

I dont suppose there should be any leak in the valves??

 

[gordfraser]

thanks for all the help. What a great forum :laugh: :laugh: :laugh:

 

[IndyMX]

No, leaks in valves are a bad thing

 

[Patman]

thanks for all the help. What a great forum :laugh: :laugh: :laugh:

If you want instant answers to your questions cough up the bucks for a factory service manual and then read it. If you want everything for free you have to wait around until somebody answers.

Quality / Speed / Price you pick two and sacrifice the third.

Maybe you should go in to a bit more detail of the history of this bike. What you are saying and what it is doing are not indicating that it has been maintained.

 

[whenfoxforks-ruled]

If the valve is not sealing, could be the seat were not cut when it got over hauled, or the valves are cupped and garbage.