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Old 02-14-2012, 06:39 PM
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low vac rough idle

I have 72 grand prix 400 the heads are shaved .060 board 20 forged pistons molly rings cast headers 1.6 roller rockers my vac is 10 - 8 psi mild cam i indicated the lifter lift on intake it seams to not close at rite time chain is in rite i adjusted lifter every way possible need help.engine runs rich with edo 650.

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Old 02-14-2012, 08:24 PM
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Its a bit hard to read your post, but double check valve lash/preload. Sounds like you might have one or more lifters bottomed out.

Pontiac heads don't come with adjustable lash, you just torque them down. If you've shaved the heads, you might have one or more lifters that aren't letting valves close fully.
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Old 02-14-2012, 09:19 PM
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Quote:
Originally Posted by curtis73
Its a bit hard to read your post, but double check valve lash/preload. Sounds like you might have one or more lifters bottomed out.

Pontiac heads don't come with adjustable lash, you just torque them down. If you've shaved the heads, you might have one or more lifters that aren't letting valves close fully.
yes stock lifers have a torque spec but the roller rockers have a spec like a chevy adjustment sorry about the first post.
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Old 02-14-2012, 09:32 PM
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Check your fuel pump pressure. Eddy carbs don't like more than 5.5 lbs. Could be flooding a bit causing rough idle and low vac readings.
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Old 02-14-2012, 10:19 PM
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Quote:
Originally Posted by RWENUTS
Check your fuel pump pressure. Eddy carbs don't like more than 5.5 lbs. Could be flooding a bit causing rough idle and low vac readings.
now thats a good one i will do that thanks. how does running rich lower the vac?

Last edited by baddme70; 02-14-2012 at 10:47 PM.
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Old 02-15-2012, 09:35 AM
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Quote:
Originally Posted by baddme70
now thats a good one i will do that thanks. how does running rich lower the vac?
Basically anything that makes it run poorly will reduce idle vacuum. Poor combustion means poor scavenging and less airflow through the cylinders, therefore less vacuum
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Old 02-20-2012, 05:19 PM
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Quote:
Originally Posted by curtis73
Basically anything that makes it run poorly will reduce idle vacuum. Poor combustion means poor scavenging and less airflow through the cylinders, therefore less vacuum
i checked fuel pressure its under 5 so thats not a problem any other idea?
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