Testing Vacuum Advance

Finally got the Pontiac started last night for another season of fun. It started with no problems but when I go to give it gas, it really bogs down. If I feather it slowly the engine will rev up ok. The choke is functioning properly and I get a good stream of fuel from the accel circuit in the carb throat when activated. It idles no problems, but whether hot or cold I've got this hesistation. I'm suspecting a vacuum advance problem. I haven't done anything to the motor over the winter - everything is as it was when I stopped running it.

The motor is a 51' 239 In-line 6, Rochester B single carb - how do I go about testing whether the vacuum advance is functioning or not ?

Thanks much for the advice !!!

 

Simple test---just clamp off vacuum line and retest. Vac can not functioning would hurt street performance but would not likely prevent engine from revving up. Likelier vac problem is that it works but the Delco breaker plate movement is wonky, allowing plate to shift eccentrically and close up points.

 

Then...two more quickies: Temporarily advance static timing about 5 degrees...if lack of vac advance is the problem, that will mask/improve the problem.
Then, slowly choke car with ether the choke plate or your less favorite hand, and revvit. If better at some level of choke, not enough gas. If worse, create a vac leak and see if leaner is better.

 

Stick a long clean hose to the advance and suck on it you can take the cap off and see if it moves.