NEW ADVICE 08 yz450f

I have a guy that wants to possibly trade his 08 450 for my 98 yz250 and he said that once the timing chain was replaced it became very hard to start but will start being pushed off. What would cause that I figured it jumped timing or not done right or a bad valve any help is appreciated

Hum I don't think it would start if the timing was off. It could be tight intake valves or even a simple plugged pilot jet.

Wouldnt those issues affect it the whole time riding

His words..... So when you kick it you can hear and feel the compression then after a few kicks it back fires really loudly and sort of acts like it wants to start

Maybe Not putting it on the compression stroke

It's easy enough to check the cam timing, valve adjustment and pilot jet.

But in the meantime, if the thing runs at all, I'd jump on that deal before he changes his mind. As long as it's not a basket case money pit.

Do a compression check.

The real question is, 'the timing chain was replaced' includes what else, exactly.

 

If he does not know, you run.

The real question is, 'the timing chain was replaced' includes what else, exactly.

 

If he does not know, you run.

Im with Krannie. Getting a dirt bike that you don't know the history on can be VERY expensive. 

 

You will spend many hours and $$$ trying to figure out what they did, or didn't do. And the frustration of a dirt bike that won't start on the side of a hill can ruin a perfect day.

Do a compression check.

 

On a bike that has automatic decompression, exactly what do you expect that would tell you?

I was thinking valves. I was told worn valves cause the intake to open slowly causing bike to be hard to start. I was told that a bump or push start would allow you to start a bike with worn valves because of the faster rotation of the valves allow. I would start there.

I was thinking valves. I was told worn valves cause the intake to open slowly causing bike to be hard to start. I was told that a bump or push start would allow you to start a bike with worn valves because of the faster rotation of the valves allow. I would start there.

 

Not quite.  Tight intake valves, or old, worn valves, leak compression.  In the case of intake valves, they leak it back into the intake and disrupt the vacuum signal from the intake stroke that pulls fuel up through the jets. 

 

The valves do not open at any different rate than they ever did, but since bump starting will usually take the engine through more than one compression stroke, and turns the engine faster than with the kick start, it can overcome the loss of compression and the intake dilution enough to get the bike started. 

 

Hearing compression in the crankcase is normal, as even a healthy engine will leak compression past the rings when turning the engine over slowly. 

On a bike that has automatic decompression, exactly what do you expect that would tell you?

 

My bad, I meant a leak down.

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