Vacuum Gage
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Pro
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From: Oneida WI
Vacuum Gage
1971 350/270hp QuadraJet How many inches of vacuum should i have at idle? Do I hook up the gage to the port where the vacuum advance goes to or where the vacuum line goes to the charcoal canister?
Burning Brakes
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From: Des Moines Iowa
Re: Vacuum Gage (Tom Johnson)
Attach gauge to a port below the throttle plates/butterflies. Port in the intake, firewall side of carberator(on #8 intake runner?) works, or believe the carb port with hose running to cannister will work as well. Don't use vacuum advance carb. port.
Melting Slicks
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From: Clifton Park NY
Re: Vacuum Gage (Tom Johnson)
1971 350/270hp QuadraJet How many inches of vacuum should i have at idle?
Thanks in advance!
-Pedro
Safety Car
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From: San Antonio TX
Re: Vacuum Gage (Pedro'74)
1971 350/270hp QuadraJet How many inches of vacuum should i have at idle?
Lemme jump in, since I was about to ask the same question. What should be my vacuum reading, approximately? My engine is an L-48, almost stock, except for cam (Crane H-272-2, 216/228 @ .05"), ignition (Pertronix) and exhaust (headers + chambered exhaust).
Thanks in advance!
-Pedro
Lemme jump in, since I was about to ask the same question. What should be my vacuum reading, approximately? My engine is an L-48, almost stock, except for cam (Crane H-272-2, 216/228 @ .05"), ignition (Pertronix) and exhaust (headers + chambered exhaust).
Thanks in advance!
-Pedro
For your cam, Pedro, around 12" to 14" and steady most likely. Perhaps a little lower if your LSA is under 112 degrees and a little higher if you're over 114 degrees.
Melting Slicks
Joined: Jul 1999
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From: Clifton Park NY
Re: Vacuum Gage (gerry72)
Thanks, Gerry!
The LSA is 112. Actually my vacuum reading is a little higher: 17-18, but with the gauge hooked up to the carb, passenger's side. Not sure if it makes a difference, but later I'll check with the gauge hooked up to the manifold.
Thanks again!
-Pedro
The LSA is 112. Actually my vacuum reading is a little higher: 17-18, but with the gauge hooked up to the carb, passenger's side. Not sure if it makes a difference, but later I'll check with the gauge hooked up to the manifold.
Thanks again!
-Pedro
Safety Car
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From: San Antonio TX
Re: Vacuum Gage (Pedro'74)
P.S. That reading is with an initial timing advance of about 24 degrees.
-Pedro
-Pedro
Melting Slicks
Joined: Jul 1999
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From: Clifton Park NY
Re: Vacuum Gage (gerry72)
Gerry,
Believe it or not, that is with the vacuum advance disconnected, and the car is running good and starts right away. The vacuum canister was hooked up to a non-ported source, which was giving a huge advance at idle, and the engine seemed to like it! :eek:
BTW, the 24 degrees of advance was obtained by setting the total advance to 36 degrees. Actually since my idle speed is a little high, and I checked the timing with the transmission in park, the centrifugal advance may be responsible for a couple of degrees of this initial advance. But anyway, the initial advance is high...
-Pedro
Believe it or not, that is with the vacuum advance disconnected, and the car is running good and starts right away. The vacuum canister was hooked up to a non-ported source, which was giving a huge advance at idle, and the engine seemed to like it! :eek:
BTW, the 24 degrees of advance was obtained by setting the total advance to 36 degrees. Actually since my idle speed is a little high, and I checked the timing with the transmission in park, the centrifugal advance may be responsible for a couple of degrees of this initial advance. But anyway, the initial advance is high...
-Pedro
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From: Fort Worth TX
St. Jude Donor '06
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Re: Vacuum Gage (Pedro'74)
Can anyone confirm the rochester carb port that the vacuum advance should be connected to? I put the Crane advance kit into my distributor and when vacuum is connected, the timing moves up from 10 degress to 34 degrees. I've backed the vacuum canister down all the way, but still haven't modified and installed the limiter they provided. What concerns me is there is quite a bit of suction on the end of the hose at idle. If I put a vauum gauge on that hose, what kind of reading should I get?
Melting Slicks
Joined: Jul 1999
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From: Clifton Park NY
Re: Vacuum Gage (74-Roadster)
Can anyone confirm the rochester carb port that the vacuum advance should be connected to?
-Pedro
Racer
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From: Lombard IL
Re: Vacuum Gage (74-Roadster)
You shouldn't get any vacuum reading from the advance port/hose at idle. I had a problem with my 80 stock Qjet that it was not ported and was providing manifold vacuum to the advance at all times. Lars and I talked it over and we weren't sure why this was.
I ended up making a modification to the base plate of the Qjet to move the vacuum source above the butterflies and now it works the way it should.
I ended up making a modification to the base plate of the Qjet to move the vacuum source above the butterflies and now it works the way it should.
Safety Car
Joined: Aug 2001
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From: Waterford Mi
Re: Vacuum Gage (74-Roadster)
Check the mechanical advance, I had the same thing with my 73 and after testing everything out I found the weights to move out at as soon as the engine started. After making sure the weights couldn't move the timing drop to 12 degrees. You may need to have it recurved.
Team Owner
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From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Re: Vacuum Gage (Tom Johnson)
Ported vacuum should read near Zero at idle and it should be hooked to the vacuum advance.
What you would normally do is disconnect the vac. advance and then with a dial type timing light check to make sure your total advance is @ 38 degrees at 3200 rpm. Just to make sure all the mech adv. is in. So your set at initial and mech = 38 most motors like 10-14 degrees initial + mech to add to your 38
You adjust the vac advance to 4-8 degrees additional. So with it hooked up timing should read 44ish on the timing light at say 3400 rpm. Then test drive for signs of ping at WOT and at highway cruise speed. If it pings at highway speed lower the vac adv. Ping at wide open throttle retard the dist initial.
What you would normally do is disconnect the vac. advance and then with a dial type timing light check to make sure your total advance is @ 38 degrees at 3200 rpm. Just to make sure all the mech adv. is in. So your set at initial and mech = 38 most motors like 10-14 degrees initial + mech to add to your 38
You adjust the vac advance to 4-8 degrees additional. So with it hooked up timing should read 44ish on the timing light at say 3400 rpm. Then test drive for signs of ping at WOT and at highway cruise speed. If it pings at highway speed lower the vac adv. Ping at wide open throttle retard the dist initial.