I have a '72 GMC Custom-1500, 350 engine/4 bbl Quadrajet 4MV, and an automatic transmission. I replaced points distributor with a HEI distributor. I don't believe advance is working. How can I check it without any special tools? Also, when I remove vacuum advance hose from carburetor, the engine idle doesn't change. Isn't idle suppose to increase or something?
2007-08-13 03:53:35 · 3 answers · asked by slowboy 2 in Cars & Transportation ➔ Maintenance & Repairs
There are two different kinds of vacuum ported and manifold. You vac advance is connected to the ported vacuum. There are two differences between these vacuum sources. Ported vacuum doesn't start until the carb plates uncover the port while manifold vacuum is constant. The other difference is that ported vacuum increase as the RPMs go up and manifold vacuum decreases. So, no you won’t see an idle change when you disconnect your advance, and no you won’t see it come on as your engine will not pull enough vacuum to pull the advance until it is under load. If you think that your advance is not working you can do the old mouth test, pull the cap and suck on the hose (or connect it to a vacuum source) the advance should move.
2007-08-13 04:07:49 · answer #1 · answered by Anonymous · 1⤊ 0⤋
If you follow the route of the vacuum advance line you will find it's plugged into the carburetor somewhere ABOVE the throttle plates. When the motor idles there's no vacuum above the plates. This is completely normal. To prove the advance mechanism is working plug it to a vacuum location below the throttle blades and place a finger beneath the vacuum canister rod that attaches to the breaker plate. Have someone start the motor. You should feel the rod pull toward you. You could also hook up a length of hose and connect it to the vacuum advance canister. Place it in your mouth and create vacuum. The canister rod will move if it's working properly.
The source location of vacuum for the vacuum advance canister was chanced in the late sixties for emissions purposes. Between you, I and the fence post your motor will run sharper if you leave the vacuum advance line plugged into a source below the throttle plates. You will find that the motor will sound less labored at idol and will pick up some RPM's. You may need to set the idol back down a bit. The motor will run better at light throttle. You may squeeze a little better fuel economy out of it.
2007-08-13 04:30:33 · answer #2 · answered by Country Boy 7 · 1⤊ 0⤋
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RE:
When I remove vacuum line from carburetor, the engine idle stays the same. Isn't idle suppose to increase?
I have a '72 GMC Custom-1500, 350 engine/4 bbl Quadrajet 4MV, and an automatic transmission. I replaced points distributor with a HEI distributor. I don't believe advance is working. How can I check it without any special tools? Also, when I remove vacuum advance hose from carburetor, the...
2015-08-07 11:39:12 · answer #3 · answered by Anonymous · 0⤊ 0⤋
check that vac. line and filter, it sounds plugged.
2007-08-13 03:58:00 · answer #4 · answered by cliffie 4 · 0⤊ 0⤋