First, are the carbs properly synchronized? If you don't
know for certain, check that first. (If I were a betting
man, this is where I'd put my $.)
If the carbs aren't properly synchronized, you could have
one carb too lean and the other too rich. It'll do okay at
idle (since the crossover tube will allow for each cylinder
to draw from both carbs at idle). But when you open it up,
1 & 2 will draw almost entirely from the front carb, while 3
& 4 will draw almost entirely from the rear (there's only so
much air the crossover will flow). The car will stumble and
backfire.
Richening the mixture in this situation will being the lean
carb up to (or closer to) correct, but make the rich carb
WAY too rich. Now it will rev, but won't idle.
Next, look for vacuum leaks, and don't forget to check the
throttle shafts for leaks. Vacuum leaks will screw up your
mixture and the balance between the carbs.
My 0.002. Hope it helps.
Chris K.
> I need a little advice on a carb adjustment. Valves
> and timing are correct. The engine will idle smouth
> but will start backfireing out the carb at about 3000
> RPM. If i increace the mixture it will reach higher
> RPM but won't idle right. Any suggestions? This is a
> 1275 in a 74 Midget.
>
> R Sexson
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