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opening in exhaust manifold
I have wondered while looking at pictures of the older and early model manifolds, what, if any, purpose the threaded opening (maybe 3/8") in the base of the manifold has. My drain plug is higher up. Probably a dumb question but just thought I'd ask.....:-) Thanks. Tim Guy
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Tim,
It's not clear to me which threaded hole you're talking about. There are two 1/8" pipe threaded holes on the side of late model manifolds, one for the scavenge tube and one in the rear which is used as a drain. Early model manifolds do not have the hole drilled and tapped for the scavenge tube.
Don -
Scavenge tube
Thanks Don, you cleared up my puzzle. Scavenge tube is the purpose which I assume there is no need for with my early model engine. If I were to place a later model manifold on my early model engine, I assume I would plug that particular threaded opening? Thanks.
TimComment
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Tim,
You're essentially correct. However, I don't want to leave you with the impression that early model carburetors do not have a scavenge tube. They actually have an internal scavenge tube that extends into a tiny sump in the bottom of the intake throat which scavenges any fuel from there and delivers it to a point approximately half way up the vertical throat of the carburetor, to be burned along with the regular fuel mixture. You can see the bottom end of this tube by looking into the intake throat.
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