Exhaust scavenging (or lack of it) is why engines with radical cam profiles don't run well at low speed. At idle, and usually midrange speeds, when the intake valve opens while the piston is still on the exhaust upstroke, a lot of the exhaust gas is forced back into the intake manifold. That reduces vacuum in the manifold, creates a rough idle, and the situation doesn't improve until enough RPM and exhaust gas velocity is achieved to begin the exhaust scavenging process. Lumpy cams radically reduce low end torque, and the result is an engine that only runs well at or near wide open throttle. Combine a radical cam, lots of carburetion and a low restriction exhaust with a cylinder head that has lousy breathing characteristics, and you end up with the sort of problems a lot of stovebolters won't admit they have. "It runs GREAT with two Rochester B's"! Maybe at 4000 RPM!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
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