kevin lane wrote:
> my new engine has been hard to start. the other weekend I experienced
> a big bang [backfire I guessed]. today I noticed my intake manifold
> has a bit of a leak! my design assumption that it would always be in
> a slight vacuum state was obviously wrong. need to check the carb I
> guess to see if anything happened to it.
>
>
>
Kevin, is that just an aluminum shoebox, bolted to a plate and then
sealed with blue-goo? Seems like it would be really simple
construction, and the side blowing out would help to protect the carb in
the case of a backfire.
The Weber is not affected by a backfire. This can also happen with injected engines. You must assume this will happen, and note that modern intake log manifolds are overly robust and the throttle bodies have thicker than needed butterflies. So when this occurs the butterfly does not fold around the throttle shaft, or stick closed from a bent butterfly or shaft.
Even the Renesis, with no overlap at all can do this. More likely a glowing carbon grain lighting off the mixture with the intake port still open. Could also be too high a heat range spark plugs. Not a timing problem if the engine is running.
Mothers 58 Olds did this for many minutes after shut down. It "ran on" as it was called back then. In the age before converters, you could slowly pour in a Coke bottle full of water into each side of the giant 4 barrel to flush away the carbon. Works on rotaries as well.
Ruins converters. Just pour the water slowly enough that the engine does not stumble at 2,000 RPM. Done just before a rebuild, the engine will be carbon free.
You could rev up the engine, shut off the ignition, and go to full throttle to chill the carbon. Worked most of the time.
The engine would die with no drama.
You must plan for this in design. The inlet right through the air cleaner should be looked at as a pressure vessel. My air cleaner cover is held on with springs. The over pressure cycles the springs and all returns to normal.
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