Posted by Vaughn [99.14.82.207] on Friday, December 18, 2015 at 11:27:51 :
In Reply to: vacumm advance functioning? posted by DDD [209.253.157.5] on Friday, December 18, 2015 at 10:33:13 :
The vacuum advance has a flexible diaphragm that cracks and allows air in the system when bad creating a lean condition. Plug the carb at the vacuum line port, if it eliminates the problem, probably bad vacuum advance. Narrow point gap will cause the condition, bad coil, lean fuel/air, etc. You're going through what most of us have gone through - debugging the truck.
If you have an IGS dist., you have both mechanical and vacuum advance, if IAT, only vacuum advance.