235 should idle at 450-500 RPM when fully warmed up. With 10 degrees mechanical advance as a base when the vacuum advance is pulled in you will get some more and that might be the issue. Set the idle down, zero the advance at idle, hook up the vacuum and set with a vacuum gauge. Adjust timing to max vacuum, then retard it some, about 1 inch mercury on the gauge. Reset idle to 450-500 Rpm, set mixture screws to max vacuum and reset idle again if needed. Try these things before you pull out your hair. For fine tuning call Langdon and get information on how to balance the two carbs. Take your time and adjust one thing at a time. Easy to get mixed up with multiple adjustments.

Steve H