low vacuum at idle

[william1]

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 can’t find any, but here’s the interesting part, I get a head brake pedal at idle, I’m 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, it’s like 6 at idle , also I have very quick hesitation when I get on the throttle.

[JohnZ]

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.

[william1]

 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]

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.