Vacuum advance 83 454 - The 1947 - Present Chevrolet & GMC Truck Message Board Network

ZacharyDouglas1992 · 01-10-2018, 02:02 PM

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

Zack

**Ironangel** · 01-10-2018, 02:09 PM

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

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

Seriously?!? Fail for ****in timing?!? Glad I don’t live in Commiefornia......

ZacharyDouglas1992 · 01-18-2018, 12:40 PM

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

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

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

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!

-klb

67 Burb · 01-20-2018, 12:45 AM

Too bad you can't just move the timing tab so it looks like is at 4 degrees with the light.

01-10-2018, 02:02 PM	#1
ZacharyDouglas1992 Registered User Join Date: Nov 2013 Location: Fowler California Posts: 140	Vacuum advance 83 454 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 Zack Attached Images __________________ 1967 CHEVELLE MALIBU 427/700R4 1971 CHEYENNE 10 350/350 1983 GMC K3500 454/400/205 1987 R10 TBI 350/700R4 2014 CRUZE 2.0 TURBO DIESEL

01-10-2018, 02:09 PM	#2
Ironangel Senior Member Join Date: Feb 2010 Location: Falls City, Nebraska "100 Miles From Nowhere" Posts: 2,219	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... __________________ Michael of the clan Hill, "Two Seventy Two's" 71 1-ton Dually 350 4-Speed 71 C/50 Grain Truck, 350 Split-Axle 4-Speed 02 3/4 ton Express 14 Indian Chief Vintage 1952 Ford 8N, "Only Ford Allowed On The Property" "Be American, Buy American"

01-10-2018, 03:04 PM	#3
ZacharyDouglas1992 Registered User Join Date: Nov 2013 Location: Fowler California Posts: 140	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. __________________ 1967 CHEVELLE MALIBU 427/700R4 1971 CHEYENNE 10 350/350 1983 GMC K3500 454/400/205 1987 R10 TBI 350/700R4 2014 CRUZE 2.0 TURBO DIESEL

01-10-2018, 03:12 PM	#4
b454rat Senior Member Join Date: May 2004 Location: Binghamton, NY Posts: 3,464	Re: Vacuum advance 83 454 Seriously?!? Fail for ****in timing?!? Glad I don’t live in Commiefornia...... __________________ 2000 GMC CCSB 454/4L80 6” lift SAS 1999 Chevy CCSB 454/NV4500 4” SAS 1999 GMC Yukon 350/4L60 6" SAS

01-18-2018, 12:40 PM	#5
ZacharyDouglas1992 Registered User Join Date: Nov 2013 Location: Fowler California Posts: 140	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. __________________ 1967 CHEVELLE MALIBU 427/700R4 1971 CHEYENNE 10 350/350 1983 GMC K3500 454/400/205 1987 R10 TBI 350/700R4 2014 CRUZE 2.0 TURBO DIESEL

01-18-2018, 01:04 PM	#6
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,707	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.

01-18-2018, 02:27 PM	#7
ZacharyDouglas1992 Registered User Join Date: Nov 2013 Location: Fowler California Posts: 140	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. __________________ 1967 CHEVELLE MALIBU 427/700R4 1971 CHEYENNE 10 350/350 1983 GMC K3500 454/400/205 1987 R10 TBI 350/700R4 2014 CRUZE 2.0 TURBO DIESEL

01-18-2018, 02:54 PM	#8
weq92f Registered User Join Date: Oct 2016 Location: Dallas Texas Posts: 3,151	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! -klb __________________ 67 C10 fleet fuel injected '70 402, 700r4, 3.73 posi 07 335 sport turbo 6sp 94 Trans Am GT LT1 6sp posi -- sold after 22yrs 99 540 sport V8 6sp -- sold 73 240z L24 4sp -- given to friend 68 C10 step 350/350 3.73 open -- sold

01-20-2018, 12:45 AM	#9
67 Burb Registered User Join Date: Dec 2011 Location: Brandon, Manitoba, Canada Posts: 548	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. __________________ Bob 1967 2wd Burb, 350/TH350, 3.73 posi



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