Vac Advance ??????
Thread Starter
Pro
Joined: Jun 2008
Posts: 673
Likes: 2
From: Melbourne Victoria
Vac Advance ??????
Greetings ALL,
Well now I'm unemployed,I get to fiddle with the Vette abit more.
This time around I decided to use my new dial back
timing light (WE LOVE TOYS !!!) Anyway I set the base timing (10*)and thought I'd check the VAC advance (running from full manifold ) and noticed an immediate jump in revs, and timing wasn't at 10* anymore ???
After some head scratching I noticed that as soon as the vac line was put on the advance can..
IT ADVANCED....but this was at idle.
So here's my questions.
Should it be advanced at idle ???
(If not) How do I adjust it (Dizzy is CRT performance
HEI tach drive)???
And Ported OR Full VAC ????
Many THANKS for continued HELP & patience.
GAV
Well now I'm unemployed,I get to fiddle with the Vette abit more.
This time around I decided to use my new dial back
timing light (WE LOVE TOYS !!!) Anyway I set the base timing (10*)and thought I'd check the VAC advance (running from full manifold ) and noticed an immediate jump in revs, and timing wasn't at 10* anymore ???
After some head scratching I noticed that as soon as the vac line was put on the advance can..
IT ADVANCED....but this was at idle.
So here's my questions.
Should it be advanced at idle ???
(If not) How do I adjust it (Dizzy is CRT performance
HEI tach drive)???
And Ported OR Full VAC ????
Many THANKS for continued HELP & patience.
GAV
Race Director
Joined: Nov 1999
Posts: 10,643
Likes: 8
From: Foxfield CO 1970 Convertible
Yep - the vacuum is highest at idle, so the hose should be disconnected and plugged (thus the set of golf tees in all the old timers tool boxes).
Yes - it should be advanced at idle. You said you're starting at about 10 degrees which is very typical. I'd set this at the smoothest idle you can. You will probably go between carb settings and timing settings to get the smoothest...
Now with the old points ignitions, you'd change weights. etc. at this point, but with HEI, I think that's about all you need to do. The vacuum from the engine will adjust the advance as needed when the engine gets off idle. You can use your timing light to check the advance at certain rpms, etc., and can experiment with what advance the engine runs best at. Usually 35 degrees or so above 3000 rpm, but it will be slightly different for each engine.
I'm sure someone with HEI will chime in...
Yes - it should be advanced at idle. You said you're starting at about 10 degrees which is very typical. I'd set this at the smoothest idle you can. You will probably go between carb settings and timing settings to get the smoothest...
Now with the old points ignitions, you'd change weights. etc. at this point, but with HEI, I think that's about all you need to do. The vacuum from the engine will adjust the advance as needed when the engine gets off idle. You can use your timing light to check the advance at certain rpms, etc., and can experiment with what advance the engine runs best at. Usually 35 degrees or so above 3000 rpm, but it will be slightly different for each engine.
I'm sure someone with HEI will chime in...
Last edited by Z-man; Sep 2, 2009 at 12:47 AM.
Thread Starter
Pro
Joined: Jun 2008
Posts: 673
Likes: 2
From: Melbourne Victoria
Got IT !!!!!
10* base & 36* (full mainifold Vacuum)
RUNS GREAT (and cooler too). Yeahhhhhhh!
I also found Vac leaks in .........GUESS WHERE ?????
The headlight setup!!!!.
So I've blocked it off for now.
(A job for another day).
After tightening the exhaust manifold bolts,
the popping from the exhaust has gone too.
Thanks Z-man ( I just thought all old timers played golf!!).
I wonder what "SHE" will throw at me next..........??????
Cheers
Gav
10* base & 36* (full mainifold Vacuum)
RUNS GREAT (and cooler too). Yeahhhhhhh!
I also found Vac leaks in .........GUESS WHERE ?????
The headlight setup!!!!.
So I've blocked it off for now.
(A job for another day).
After tightening the exhaust manifold bolts,
the popping from the exhaust has gone too.
Thanks Z-man ( I just thought all old timers played golf!!).
I wonder what "SHE" will throw at me next..........??????
Cheers
Gav
Race Director
Joined: Nov 1999
Posts: 10,643
Likes: 8
From: Foxfield CO 1970 Convertible
It's amazing how many engines run badly due to leaks in the headlight system or the heater vent system. These are extensions of the manifold vacuum, so any leaks there actually make the engine run badly. Sounds like you caught it...
How are those brakes? How about those seat backs - loose? Maybe that carpet is pretty worn?
She'll keep you on your toes!
How are those brakes? How about those seat backs - loose? Maybe that carpet is pretty worn?
She'll keep you on your toes!
Melting Slicks
Joined: Apr 1999
Posts: 2,010
Likes: 3
From: Moon Twp. PA USA
Got IT !!!!!
10* base & 36* (full mainifold Vacuum)
RUNS GREAT (and cooler too). Yeahhhhhhh!
I also found Vac leaks in .........GUESS WHERE ?????
The headlight setup!!!!.
So I've blocked it off for now.
(A job for another day).
After tightening the exhaust manifold bolts,
the popping from the exhaust has gone too.
Thanks Z-man ( I just thought all old timers played golf!!).
I wonder what "SHE" will throw at me next..........??????
Cheers
Gav
10* base & 36* (full mainifold Vacuum)
RUNS GREAT (and cooler too). Yeahhhhhhh!
I also found Vac leaks in .........GUESS WHERE ?????
The headlight setup!!!!.
So I've blocked it off for now.
(A job for another day).
After tightening the exhaust manifold bolts,
the popping from the exhaust has gone too.
Thanks Z-man ( I just thought all old timers played golf!!).
I wonder what "SHE" will throw at me next..........??????
Cheers
Gav
I never set, and I don't care about what the timing is at idle. I just set mine at 34*, all in by 2600 RPM, with vacuum line plugged. Timing at idle is what it is.
My vacuum advance adds another 16* when hooked up, for a total initial+mechanical+vacuum of 50*.
Thread Starter
Pro
Joined: Jun 2008
Posts: 673
Likes: 2
From: Melbourne Victoria
You are checking for 36* with the vacuum line disconnected and plugged? At what RPM are you getting 36*? Should be at less than 3000RPM.
I never set, and I don't care about what the timing is at idle. I just set mine at 34*, all in by 2600 RPM, with vacuum line plugged. Timing at idle is what it is.
My vacuum advance adds another 16* when hooked up, for a total initial+mechanical+vacuum of 50*.
I never set, and I don't care about what the timing is at idle. I just set mine at 34*, all in by 2600 RPM, with vacuum line plugged. Timing at idle is what it is.
My vacuum advance adds another 16* when hooked up, for a total initial+mechanical+vacuum of 50*.
Got it sorted
I've now got the same settings as glen242
and they're spot on.
MATE !So that's that sorted,
Now to replace my Tach cable
I also "found" a "tru-flex" type hose (that I'd stashed
away years ago, before I had the Vette) and it's
the the right size
to replace my lower radiator hose (and the wife complains that I collect "junk"
and never use it).It's stainless & was originally from a Boiler pump.
Cost big dollars IIRC.
Lucky I "found" it & gave it a good home (before the factory closed)
.So that's saved me some dollars .....
(I'll tell the wife $150
).Again THANX everyone for your continued HELP,
Gav
