Micheal,
Hello fellow Albertan!
Jim leach made some good points and I concur but a surge is usually
electrical or fuel related. I am going to make an assumption that the timing
chain is not really loose, that all of the valves are evenly adjusted. I
have run some pretty radical engines and it is not uncommon for some loading
of the engine at low RPM and that has caused some stumble, but yours sounds
like a more prolific stumble as I interpreted that you can feel it as you
cruise at constant speed at 2000-3000 RPM. Have you scoped the engine to
determine if a plug wire is bad? (Cheaters test is to run the engine in
pitch dark and look for the light show) It would seem unusual that the
condition is repeated with three diff. carbs as that is what i would have
guessed. Is the distributor vacuum or strictly mechanical advance? Most
curves are all in by 3000 and if your advance is sticking or has an uneven
vacuum signal it may be bouncing around at 2000-3000 that would explain the
surge.(Have you watched it with a timing light at all RPMs) Could it be fuel
distribution through the intake as with the ported heads and big cam overlap
could it be that there is a resonance generating inside the intake causing
uneven cylinder filling at low RPM? Last suggestion is to advance the cam 4
degrees to see if that lowers the surge RPM. Aside from the points made it
sounds like a head scratcher and if anything else comes up I will send the
idea.
Good Luck,
Tim Ronak
Cochrane AB
B382000680
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