engine off vacuum
Thread Starter
Burning Brakes
Joined: Nov 2004
Posts: 1,028
Likes: 0
From: San Antonio Texas
engine off vacuum
my distributors vacuum advance holds vacuum with the engine off. even if off for several days, if hose is disconnected from vacuum canister you can hear the rush of air when the hose is pulled off. is this normal?
Instructor
Joined: Mar 2003
Posts: 195
Likes: 0
From: Eagle Wi
If you pull the hose off the carb end does it do the same thing?
If not it's possible the hose is bad. I have seen hydraulic hoses were a flap of the rubber comes loose on the inside and it acts like a little check valve. Just a thought.
If not it's possible the hose is bad. I have seen hydraulic hoses were a flap of the rubber comes loose on the inside and it acts like a little check valve. Just a thought.
Thread Starter
Burning Brakes
Joined: Nov 2004
Posts: 1,028
Likes: 0
From: San Antonio Texas
hmmmm... good question. i'll have to go out and check it.
also, there is a small, thin, disk shaped "filter???" in the middle of the hose. is that "stock" or a Bubba modification?
also, there is a small, thin, disk shaped "filter???" in the middle of the hose. is that "stock" or a Bubba modification?
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Instructor
Joined: Dec 2002
Posts: 242
Likes: 0
From: Port Orchard Washington
Vacuum advance for a 79 comes off of the base of the carb (look at your emissions sticker, it will show which side in the front. Should be the pass. side) and goes straight to the advance canister with nothing in between. Sounds like someone put the headlight vac. check valve on the advance line, which is wrong. Effectively it is giving you full advance always, which is great for fuel mileage but difficulty in starting and too much adv. at full throttle means low power and detonation.
Pro
Joined: Apr 2004
Posts: 687
Likes: 0
From: Atascadero Ca
can you take us a picture? That would help alot. Sounds like someone installed a check valve to me too. Remove the line altogether and run a new one and see if that helps, worst that can happen is you're down 50 cents for the vacuum line
Thread Starter
Burning Brakes
Joined: Nov 2004
Posts: 1,028
Likes: 0
From: San Antonio Texas
i removed it already. can't really tell any difference in the way it runs. checked timing and i've got 12 degrees initial timing. another twenty at idle with or without the check valve in. that doesn't sound right either. any ideas
Instructor
Joined: Dec 2002
Posts: 242
Likes: 0
From: Port Orchard Washington
If you go to an auto parts store website that has the word "zone" in it (forum rules) you can print the vacuum diagram for your year vette. For a 79 with federal emissions the dist. line starts at the base of the carb, in the front, all the way left. It then goes to a thermal vacuum switch (eliminating advance until approx.126 degrees), then to the dist. Your advance should give approx. 16 degrees at 17" vacuum. Since you know the diaphram is good, check that the reluctor ring (can attaches to) moves when vacuum is applied.
The timing specs (also at the website) shows 12 degrees initial for the 225hp, 6 for the base motor. It looks like you are getting some mech. advance, but no vac. advance. You can attach the vac. advance line straight to intake manif. vacuum (nipple behind carb) with no problems if you don't have the original carb.
The timing specs (also at the website) shows 12 degrees initial for the 225hp, 6 for the base motor. It looks like you are getting some mech. advance, but no vac. advance. You can attach the vac. advance line straight to intake manif. vacuum (nipple behind carb) with no problems if you don't have the original carb.
Thread Starter
Burning Brakes
Joined: Nov 2004
Posts: 1,028
Likes: 0
From: San Antonio Texas
no, i'm getting vacuum and mechanical.
12 initial (79 L-82). that's correct.
when attaching vacuum hose at idle another 20 for 32.
and another 20 mechanical all in by 2500-3000 (didn't take exact measurement) for total timing of 52. that should be right, no?????
12 initial (79 L-82). that's correct.
when attaching vacuum hose at idle another 20 for 32.
and another 20 mechanical all in by 2500-3000 (didn't take exact measurement) for total timing of 52. that should be right, no?????