I finally took it to the shop

[YFZer]

I took the yfz to the local Yamaha shop and got them to do a diagnosis on it. They found out that the top end is shot from a leak down test and it only showed 25 on the compression gauge. I still dont understand why the quad still could run good and not smoke any with it losing that much compression. They said it didnt have enough compression for cold starts. What do u all think?

[intruder]

Your valves could be out of adjustment.

[exboomer]

Your situation doesn't make sense. That engine should not run at all if it only has 25 psi compression. Why did you bring the quad into the shop in the first place??? A leak down test and a compression test are two different tests. I agree with intruder, your valves may be tight if your having cold start problems. If they did a leak down test, they should be able to tell you exactly where you are losing cylinder pressure (either past the rings or past the valves). Was the leak down test performed when the engine was cold? If the leak down test showed pressure lost past the rings, you will need top end work. If the test revealed leakage past the valves, you may have a burned valve or they may be out of adjustment. Check the adjustment first.

[czrider263]

a leak down test is different than a compresson test i believe. showing 25 on that kind of test would show that you have 25% of what you oculd have?

[exboomer]

A leak down test reveals the percentage of pressure lost from the combustion chamber. So if you put 100psi of pressure in the cylinder and you have a number of 25, that means you have 25 or 75 percent leakage depending how the dealer is telling you the number. Probably, somewhere around 10 percent leakage would be the max. Where is the air leaking? If past a valve. check the adjust first.

[czrider263]

Originally posted by exboomer
A leak down test reveals the percentage of pressure lost from the combustion chamber. So if you put 100psi of pressure in the cylinder and you have a number of 25, that means you have 25 or 75 percent leakage depending how the dealer is telling you the number. Probably, somewhere around 10 percent leakage would be the max. Where is the air leaking? If past a valve. check the adjust first.

Yeah thats what i was trying to say thanks