vacuum problems

[bobarthur]

I have a vacuum problem with my 1966 GTO. It is a stock 389 4bbl automatic.
The block has been bored .040 over and the heads have been fitted with screw-in
rocker studs and big block chevy adjuctable rockers. The pistons have had .060
removed to lower the compression ratio. The cam is an Ultradyne(H6818) with a duration
of 272/276 and a .454 lift and 112 degree lobe separation.
I replaced the original Carter AFB with an Edelbrock EDL-1406. After isolating
all the vacuum accessories, the vacuum reading does not exceed 16 inches after
adjusting the ignition timing for maximum vacuum.
Do I have a bad intake manifold. How do I check it?

[bobarthur]

I have a vacuum problem with my 1966 GTO. It is a stock 389 4bbl automatic.
The block has been bored .040 over and the heads have been fitted with screw-in
rocker studs and big block chevy adjuctable rockers. The pistons have had .060
removed to lower the compression ratio. The cam is an Ultradyne(H6818) with a duration
of 272/276 and a .454 lift and 112 degree lobe separation.
I replaced the original Carter AFB with an Edelbrock EDL-1406. After isolating
all the vacuum accessories, the vacuum reading does not exceed 16 inches after
adjusting the ignition timing for maximum vacuum.
Do I have a bad intake manifold. How do I check it?

[TinInjun]

The first thing we need to know is, how does the engine run? If you have a steady needle at 16" with no engine miss, you may not have a problem. Why are you adjusting your timing using a vacuum guage? You should be using a timing light, then adjust your idle mixture to the highest reading with the vacuum guage. If you think you have a vacuum leak, use a propane torch (un-lit) and move it around the intake manifold. If there is a leak, the engine idle will speed up where the leak is. If all else fails, check your cam timing. Late cam timing will also a cause low manifold vacuum reading

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"Run wild with an Indian, not with the crowd in a Chevy"
Check out my restoration at http://members.aol.com/jetmech15/gto

[bobarthur]

I tried the propane torch. I get no increase in idle speed. Could this be retarded
cam timing? How do I check the cam timing without removing the timing chain cover?
I don't beleive the cam is at all radical.

[This message has been edited by Ccass (edited 11-13-2000).]