Hi Bill, thanks for the offer of help in diagnosis. The Carb currently on the
car is an edelbrock 600 cfm vacuum secondary. My first guess was a lean
misfire so I richened the rod/jet combination with no improvement of the
uneven condition (ie. it still bucked/surged). We also tried a Holley vacuum
secondary, and a Holley 'double pumper' carb that each ran well on a different
engine but did not run well on mine as it turned out.
I am currently eyeing the MSD, it occured to me that it only has multiple
sparks up to 3000 RPM. Perhaps an overly rich mixture would ignite unevenly
with the MSD producing the 'surge'(?). My latest mechanic has all of the
diagnosis tools I could want, and his exhaust analyser indicates a rich
condition, but I would not normally expect that to produce such uneven power.
My biggest problem is that the engine is much more radical than anything I
have worked on: my efforts were all on 'stock' fuel injected cars. The first
two mechanics I took it to are bright guys but don't have equipment to
diagnose MSD, nor monitors to read exhaust gases.
The current guy pulled the distributor and checked it on a synchograph because
he felt that the advance was wrong. I think his test proved that the first two
guys were correct and that he had read the timing wrong himself. Next step is
to correctly dial in the Carb using the exhaust analyser, I just couldn't come
up with a theory that would make an overly rich engine run this way. It really
feels lean. If that solves the problem, then great but I really wonder.
Feel free to guess, I certainly am.
Michael
|