Another carburetor and vacuum question - Team Camaro Tech
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post #1 of 5 (permalink) Old Sep 28th, 05, 09:52 PM Thread Starter
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Another carburetor and vacuum question

When a vacuum hose is pulled loose and the idle speed picks up, what does that mean? Running rich?

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post #2 of 5 (permalink) Old Sep 28th, 05, 11:09 PM
 
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Talking Re: Another carburetor and vacuum question

Not necessarily, it just means there is a vacuum leak and the engine isn't working against any negative pressure, so it speeds up, basically like simulating the throttle plates opening a bit.

Last edited by BreathWeapon; Sep 29th, 05 at 05:31 PM.
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post #3 of 5 (permalink) Old Sep 29th, 05, 07:46 AM
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Re: Another carburetor and vacuum question

Basically it means the engine is getting more air, therefore it runs faster.
An engine idling with no load is not real fussy about mixture, at least as far as it's ability to keep running. Since most of us are running a fairly rich idle mix, a vac leak will rarely lean the engine so much that it stops. Unless it's huge, a vac leak WILL NOT change the reading on your vac guage much at all, the engine will use the additional air and speed up and the vac reading will remain close to where it was without the leak.





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post #4 of 5 (permalink) Old Sep 29th, 05, 10:35 PM
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Re: Another carburetor and vacuum question

Quote:
Originally Posted by JimM
Basically it means the engine is getting more air, therefore it runs faster.
An engine idling with no load is not real fussy about mixture, at least as far as it's ability to keep running. Since most of us are running a fairly rich idle mix, a vac leak will rarely lean the engine so much that it stops. Unless it's huge, a vac leak WILL NOT change the reading on your vac guage much at all, the engine will use the additional air and speed up and the vac reading will remain close to where it was without the leak.
Somewhat true, a vacuum leak into the common plenum will not cause any vacuum guage changes (if it does not cause a missfire), a vacuum leak that affects only one or two cylinders can cause some funky stuff to happen with a vacuum guage. It all depends on where the leak is.

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post #5 of 5 (permalink) Old Sep 30th, 05, 08:57 AM Thread Starter
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Re: Another carburetor and vacuum question

Quote:
Originally Posted by Joekool1234567
Somewhat true, a vacuum leak into the common plenum will not cause any vacuum guage changes (if it does not cause a missfire), a vacuum leak that affects only one or two cylinders can cause some funky stuff to happen with a vacuum guage. It all depends on where the leak is.
I was interested in the difference between a vacuum leak at the intake gasket and a hose. I understand now. So for a normal vacuum reading the gage needle vibrates back and forth centered over the correct number. A vacuum leak affecting only a specific cylinder will make the gage needle move differently, more erratic?

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