manifold vacumm drops at idle
Thread Starter
Melting Slicks
Joined: Dec 2000
Posts: 2,130
Likes: 1
From: mesa,az
manifold vacumm drops at idle
so i hook the vacuum gauge to a manifold port on the holley 650 on top of my 327. i have an edelbrock hyd cam. 234/244 dur., .488/.510 lift 112 LC. it starts and idiles about 800 rpm with a steady reading of 7-8 in@Hg. as i turn the idle mix screws the vacume and the idle rise till i am getting about 12 in@Hg( about where edelbrock says it should be ) still steady but idling about 1100 RPM. i turn the idle speed screw to bring down the idle and the manifold vacuum drops back to 7-8 in. WTF. any ideas.
thanks
thanks
Race Director
Joined: Sep 2004
Posts: 11,874
Likes: 263
From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
whats the problem?...first use a manifold vaccum line not one from the carb if you can ...tune the a/f to get highest vacuum then set the idle speed.....all is good..... your low vacuum is probably as a result of your cam..
you may also benefit from a vaccum cannister on the distribuotr that pulls full vaccum at a low vacuum reading.
are those durations at 50? i couldn't find the cam card for that cam but if those durationsons are at 50 thats a pretty healthy cam...the cam card should give you some idea what vacuum you can expect
you may also benefit from a vaccum cannister on the distribuotr that pulls full vaccum at a low vacuum reading.
are those durations at 50? i couldn't find the cam card for that cam but if those durationsons are at 50 thats a pretty healthy cam...the cam card should give you some idea what vacuum you can expect
Last edited by bobs77vet; Jan 16, 2006 at 04:52 PM.
Le Mans Master
Joined: Jan 2000
Posts: 8,918
Likes: 27
From: New Hill NC
I am going to assume that you are reading actual manifold vacuum and not a ventury vacuum port? With that much cam, you will need a very fast acting vacuum advance to get a steady idle, like the SHP engines had.
