Weber Backfiring

[jhirasak]

Jim,

Before you start changing emulsion tubes to correct your over rich idle and main circuit transition situation, I would suggest that you make sure that the idle circuit is properly jetted since it affects the fuel/air ratio during the transition to the main circuit.

You mentioned that it appeared to run fine while it was cold but began to backfire and pop after it warmed up. If the idle circuit was jetted correctly, it would cough and spit back out of the carbs when cold and then behave normally after the engine has fully warmed up. The first thing that I would try was to incrementally decrease the size of the idle fuel jet until it idled without any hickups when hot. Having done this, I think that your rich main circuit transition situation will have improved. Once the idle circuit performs properly, then you should go to work on the main circuit and emulsion tubes.

By the way, it is a lot cheaper and easier changing idle fuel jets than emulsion tubes.

Just my 2 cents.

John