Solex carburators

[John Larson]

".................................but I have never
seen backfiring up through the carb that is caused by the carb itself
being out of tune."

Hi, Per.
              (1) Lean condition. Air leak or improperly set mixture screw.
              (2) Weak or otherwise bad accelerator pump or missing pump
jet.
I see this all the time in Bugs and carburetted Porsches, all of which we
see for service on a daily basis. Common symptom.  In fact, on carbed 911s,
even slight throttle shaft wear will cause it.