Author Topic: low vacuum at idle  (Read 1848 times)

william1

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low vacuum at idle
« on: August 29, 2009, 06:04:21 PM »
Where do I start, after getting heads reworked on my 302ci 69 z and reinstalling I now have low vacuum at idle, this engine has modifications to it pistons 12/1, cam not sure but not stock by any means manifold, 750 dual pumper 4779-s, headers, HEI
I have checked for leaks and canít find any, but hereís the interesting part, I get a head brake pedal at idle, Iím checking the booster for leaks.
We used the valve adjustment  26/26 90 degrees before and after TDC , instead of the standard 30/30 at TDC, advance 33, could I have created a late valve lag to the point I have low vacuum, itís like 6 at idle , also I have very quick hesitation when I get on the throttle.

JohnZ

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Re: low vacuum at idle
« Reply #1 on: August 30, 2009, 01:35:06 AM »
Where do I start, after getting heads reworked on my 302ci 69 z and reinstalling I now have low vacuum at idle, this engine has modifications to it pistons 12/1, cam not sure but not stock by any means
We used the valve adjustment  26/26 90 degrees before and after TDC , instead of the standard 30/30 at TDC, advance 33, could I have created a late valve lag to the point I have low vacuum, it’s like 6 at idle , also I have very quick hesitation when I get on the throttle.


The procedure outlined in my "30-30" cam lash adjustment procedure (.026" cold, using the indexing procedure exactly as described) is ONLY FOR THE FACTORY '30-30" CAM, and will produce 9"-11" Hg. of manifold vacuum at a 900 rpm idle. If you don't know what aftermarket cam is in it, you need to find out and follow the cam manufacturer's instructions on the cam card for hot or cold valve lash.
'69 Z/28
Fathom Green
CRG

william1

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Re: low vacuum at idle
« Reply #2 on: September 02, 2009, 01:29:53 PM »
 thanks johnz, went back to the old school method vacum now up, but short of trying to put a degree wheel on this thing, this will have to do for the moment.

L78 steve

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Re: low vacuum at idle
« Reply #3 on: September 16, 2009, 04:59:22 PM »
Check your booster.I just had that happen on a orig. 69. The idle was so weak turning the steering wheel would stall the engine,not enough power for the P/S. Hard pedal at idle also.
69 Z/28 Dover White X33,ZL2,PS,M20,Std.int.04C
67 SS/RS Mt. Green 1W,2LGSR,3SL,4K,5BY,07C
70 Nova L78 Blk. Cherry,Sandalwood,M21,02B