Low compression

[stephen.]

Hi all, I have one cylinder ( number 5 ) that is running very weak. Number 6 is just on the weak side of OK. I have done a compression check, 140 and with oil on the rings 150 psi. I dont think this is low enough for a valve to be not seating enough / burnt to give me a weak mixture. I think the problem lies with an air leak in the inlet manifold gasket.
I know 140 is low with 9:1 pistons but I am reluctant to remove the head if I dont have to and will not strip and rebore / re ring the engine as with so many other projects on the go, I wont ever get it back together.
What do you think ? A valve or a manifold :( :( gasket ?
Steve

[Heuer]

Go for the easy option - change the manifold gasket! Before that you might want to check the front carb to ensure the piston is moving freely, the needle is centred, is not damaged and the mixture is set correctly.

[christopher storey]

Stephen; one way to check for a manifold leak is, with the engine hot and idling, to squirt a flammable solvent such as wd40 at the joins between manifold and head, and carbs and manifold. If any change in engine running occurs, this is a sure indication of a leak

Also it's worth checking your servo hoses etc

[Larry Wade]

Hi Stephen,

I strongly recommend that you get a leak down test done before anything else. That will tell you if you have a leak and where it is going.

Larry

[Moeregaard]

I'm with Larry. This one smells like a head-gasket problem.