I was about to embark on this mission -evening the fuel distribution.  Do you happen to have any photos?  The "crack the throttle plate" trick doesn't work on my plane.  I need to pull out several inches of MP before I get a good balance and can run LOP.  I have one cylinder that is really rich, three are pretty close.  How tight were you able to get the EGT spread?  How tight is needed to good LOP operation?

Thanks,  Chris Zavatson

Chris, I have done a lot of A/F ratio work on carbureted auto engines.  A good carbureted engine is usually at its best at WOT and will run within 1 to 2 A/F's.  At part throttle this spread gets worse.  I have seen a 6 A/F spread at part throttle on a production auto engine.  An average fuel injected engine will run within 0.7 A/F at all loads.  The good GAMI injected engines are running less than 0.5 A/F spread.

When working this problem, remember that fuel is the problem.  Getting the same amount of air to each cylinder is pretty easy.  Getting the same amount of fuel to each cylinder with a carb is difficult.  The carb heat trick is cleaver if you have plenty of power.  I can't tell you any easy fixes.  Carb spacers sometimes help.  Also remember, the exhaust gas temperatures at each cylinder don't mean anything.  What matters is, at what fuel rate does each cylinder peak.  If the fuel rate is identical for each cylinder at peak exhaust temp (regardless of actual temp) then you have perfect A/F ratio spread.  The only "big" thing I can remember that caused bad A/F ratio spreads was sharp corners/tight bends.  I found that tight bends in the intake manifold runners would cause the fuel to "fall out" of the air and create a lean cylinder.  Another thing to think about....a rich cylinder is one that is working good as the fuel is staying suspended in that runner.

Craig Berland