09-05-2025, 11:24 AM
(This post was last modified: 09-05-2025, 11:26 AM by Malcolm Parker.)
I would check that the steel plate on the exhaust manifold is absolutely flat. It may have distorted slightly when the exhaust pipes were welded on. With this type of manifold set-up there is quite a lot of strain on the fixings into the block, unless they are good and tight you could get leakages. If I was getting a hissing noise my first instinct would be to look at the plugs. Have you tried turning the engine over in neutral on the starting handle (with the ignition off!) and listening carefully to the spark plugs?