try to help solve some stumble problems.
Please note tuning by vaccuum ONLY tunes in the idle circuits and the idle advance
A poorly tuned idle can cause issue with off idle stumble, and so can a poorly adjusted accel pump, as can a poorly designed cent advance curve , and a VA unit that has not been adjusted to the vaccuum requirements of the engine.
Getting the idle ciruits of the carb and the idle advance, tuning with a vacc gauge, is just the start of removing a stumble
Keep in mind as u adjust the dizzy initial , u are also adjusting how fast/ slow the cent comes in under load , and adjusting full WoT power above when the cent is all in.
So it really becomes a matter of having the idle u want , or having the power when the wheels are turning
Dialling in an engine is NOT simply looking at 1 part of the engine specs... its establishing correct mixtures and timing for WoT , idle AND cruise, each individually, then moding the carb cruise idle and WoT circuits.... plus the idle, initial , rate of curve, total and the VA in the timing.
And that CAN NOT be done with a vacuum gauge..
At minuim a measured distance and stop watch and vaccuum gauge...which is very hit in miss when compared to using Data logger with min of rpms and O2... preferably O2 IMAP TP sensor and knock sensor
Regardless do not have the initial +cent+ VA exceed 40/ 42 degs without using a knock sensor.... and check that after tuning the idle in...