If you study the runner layout of the tri-power intake manifold it would kinda make you think that there was a problem with the rear carb.
So, I isolated the rear carb from the others, ran the engine, and found that the rear carb is flowing fuel as it should. Lots of fuel coming from the boosters when you open the throttle.
Very interesting.... I'm not sure what's going on... or how to proceed. Any ideas? Stagger the jets between the front and rear carbs?
