Low Vacuum

[Joel Talka]

Hello Everyone...

I'm looking for some guidance on a problem which I am having with the '66 Coronet which I bought recently.

The car has a 318 in it now with a non-stock cam (unknown), Edelbrock 4BBL intake, Edelbrock AVS-2 carb, headers and pipes. From what I can tell, the block, pistons and heads are stock. It runs and will drive but not a lot of power to say the least.

Problem is that it makes very low vacuum as measured at the carb port, low like 5" Hg, not enough to pull the vacuum can. Smack your hand over the carb when it is running and the vacuum is certainly weak. I'm trying to figure out why.

I've done a compression test and I get numbers ranging from 105 to 130, most about 115. I've reseated the carb looking for possible air leaks, none found. Basic timing appears to be about 25 degrees but I have not messed with that, yet.

At this point I am thinking either valves or perhaps even timing chain.. The good news is that I am going to pull it and replace it with a crate motor over the next few months but would like to figure this out in any event.

I appreciate your thoughts....

Thanks,
Joel

 

[pnora]

Smack your hand over the carb when it is running and the vacuum is certainly weak. That is a test I never saw in any manuals. Better get a patent on it. If in fact that was all the vacuum it would barely run. Check it at the intake or pcv port.

 

[HALIFAXHOPS]

A can of carb cleaner is your best friend looking for leaks, Give it a small shot down the carb when running see if the ide goes up or down, then around all the usual vacuum leak areas, carb base, intake, brake booster etch if it mimics that up or down you found the area the leak is at.

 

[Joel Talka]

Smack your hand over the carb when it is running and the vacuum is certainly weak. That is a test I never saw in any manuals. Better get a patent on it. If in fact that was all the vacuum it would barely run. Check it at the intake or pcv port.

 

[Joel Talka]

Yep, that trick my uncle taught me like 50 years ago...

 

[Joel Talka]

A can of carb cleaner is your best friend looking for leaks, Give it a small shot down the carb when running see if the ide goes up or down, then around all the usual vacuum leak areas, carb base, intake, brake booster etch if it mimics that up or down you found the area the leak is at.

 

[Joel Talka]

Great idea, thanks!