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ZacharyDouglas1992 01-10-2018 02:02 PM

Vacuum advance 83 454
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I need to know whether or not my vacuum advance goes to ported or manifold vacuum on my 454. I have all factory emissions hooked up (ca smog). i'll attach the diagram for my truck. It shows it going from the back of the carb, through a check valve (which is also connected to spark tvs).

thanks for any help. loosely related...

I've got the truck running ok, but its wanting more advance. I currently have it at 6 BTDC. The factory spec is 4 BTDC, 6 should be within the acceptable margin for smog. Motor specs are relatively stock, so is there adjustments to the carb I need to make to help? at 12-16 BTDC it runs pretty fantastic. But, at least for the smog, I can't have it that advanced.

thanks for any advice


Ironangel 01-10-2018 02:09 PM

Re: Vacuum advance 83 454
Listen to what your motor likes. Gasoline was a hellofalot different than whats in the tanks today so you'll probably never match the factory specs. I run my BBC at 16 - 18 degrees BTDC at idle...

ZacharyDouglas1992 01-10-2018 03:04 PM

Re: Vacuum advance 83 454
I agree with you on the fuel, and I will have it a lot more advanced normally.

However part of the smog will be having my timing checked with a timing light. I will get an immediate fail if my timing is more than a couple degrees from 4 BTDC.

b454rat 01-10-2018 03:12 PM

Re: Vacuum advance 83 454
Seriously?!? Fail for ****in timing?!? Glad I don’t live in Commiefornia......

ZacharyDouglas1992 01-18-2018 12:40 PM

Re: Vacuum advance 83 454
I am going to venture to guess that there aren't a lot of us on here having to deal with this. I am going to run some octane booster and hi grade fuel, and get it good and warm before I take it in, and hope for the best.

geezer#99 01-18-2018 01:04 PM

Re: Vacuum advance 83 454
It’s the same up here.
We had to reduce the timing on my old 67 250 to 6 degrees from 14 and lean down the mixture screw a bunch to pass.
I don’t understand there thinking. Running it like that creates more pollution. Fine tuning saves gas and creates less pollution.

ZacharyDouglas1992 01-18-2018 02:27 PM

Re: Vacuum advance 83 454
That's essentially where I'm at now. I have the timing down to 6 degrees. I'll be leaning out the carb and running good fuel. It seems to really prefer 16 BTDC or so, and it really sounds sad at 6.

It is funny to me to take something that is running really smooth, and bog it down on purpose for the sake of the test. I'm certain that if you tested the tailpipe in both, it would be much cleaner the way I have it tuned vs how I will have to de tune it to take it in for the sniffer.

weq92f 01-18-2018 02:54 PM

Re: Vacuum advance 83 454
Good thing this test isn't imposed more often so you can get away with running 'em the way they were meant to be run!


67 Burb 01-20-2018 12:45 AM

Re: Vacuum advance 83 454
Too bad you can't just move the timing tab so it looks like is at 4 degrees with the light. :haha:

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