About 8 months ago I had a heating problem when running around town. Turned out it was my vacuum advance pot. I replaced it with a Napa VC1810 which gives 16 degrees at 8 inches of vac. Today I was doing my summer tune up and noticed that there was no advance when I hooked up the vacuum line. Yup. You got it. Vacuum advance pot was blown. Leaked like a sieve. I looked at my vacuum when I was setting up the carb and I get a full 17 inches at idle. Is that too much or did I just get a weak sister vacuum pot last time?

Thanks for the help.

Geek

 

No, no such thing as too much engine vacuum. At higher engine speeds when at no load, you can see alot more vacuum than you will at idle.

The rating for the VC1810 is the amount of vacuum it takes to cause it to advance the ignition to the full amount (in this case, 16 degrees advance at 8" of vacuum), not the maximum vacuum it is rated for "destruction".

Just make sure you are seeing vacuum from the carb/manifold port at idle (also called full time vacuum). You may have it connected to a "ported source", where vacuum is available only above idle. Ported vacuum is not advised either (for economy, smooth running, and overheating issues). Full time vacuum is how most engine run best.

If you do have vacuum at idle, and the vacuum advance is not pulling in, check it for leakage (blown diaphram most likely), or binding of the plate/linkage (rare).

You can check a diaphram by removing the dist. cap, and pushing the link in / rotating the points plate (same as if there was vacuum applied). Then while the diaphram is pushed in, put your finger over the vacuum advance port to seal it (might need to wet your finger a tad to get a good seal). Stop pushing in the link, and the diaphram should stay "in", until you remove your finger from the port (at which time, the diaphram should push the link / rotate the points plate back out).

Plasticman

 

John,
The diaphram is totally blown on this one which is why I ask if I have too much. I have a stock 327/300 where the vacuum for the advance comes right off the front of the Carter AFB. That's where I measured the 17 inches. Hopefully I just got an advance pot with a weak diaphram and the replacement one will fix that.

Thanks

geek

 

Check your vacuum hose for the presence of gasoline. If present, it can eat up your vacuum diaphragmn. A loop, either up or down in the source line will prevent this.

 

While the 17" sounds high for your set-up, it should not be enough to blow the diaphram. I would question your gauge. 17" is about half an atmosphere, a good hooker from Nevada can do better.

 

A VC 1810 is too aggrassive a vac can for your 327-300. A Borg Warner
V 325 pulls full advance (16*) at 15 " HG. It is stamped B 22 on the flange. Its spec is 2 " below your idle vacuum which is what you want.

16" to 19" vacuum is the norm for base engine 327.

 

Thanks guys. Answers in order: No gas in the line. Gauge matches two others I have used (just to be sure I was seeing the numbers right). Will see if I can find the Borg Warner pot and substitute it. Can't hurt as I am waiting for my Napa guy to get the 1810 here.

Geek

 

I agree that the VC1810 is too aggressive for the 300 hp SB (man, if Duke were still here . . .) the 1810 is a good choice for solid lifter SBs running the lopey 30-30 or the Lt-1 cam that don't pull much more than 10-12 " of vacuum. For your 300 hp SB, I think you be wanting the VC 1802 - that's a B22 stamped can.

 

Thanks. Turns out I had to order the 1810 but the 1802 they have in stock - so tomorrow I will get both and see what gives me the best results. It's getting to the point where pulling the distributor and getting it back in the right place is getting easy.

Again thanks for all the help.

Geek

 

 

Are you pulling the distributor to replace a vacuum advance?

 

Yup. Those two little screws are just begging to be dropped and fall into a bad place. So I pull it and when I drop them, it's on the bench and nowhere else.

 

Fair enough.

 

Jack - Took your advice and installed a VC 1802 - only my NAPA store tells me that number is superceeded by a VC 680 now - which is what I really put in there. Worked fine. Hot day, in town, stop and go, temp never went over 175 degrees. It doesn't ping and it seems to still have some bone in the lower end. So I am happy. Thanks for the steer there.

Gary

 

glad it worked out, I know the feeling when you get it to run right for once . . .