What am I missing?

My buddies 56 Nomad, 327, 10 to 1 comp, hydraulic roller cam, MSD dist and box.

We changed the Torker manifold to a Performer, with a 670 Holley street avenger, now the thing will only run with the vacuum advance disconnected, and not that great, but it is driveable to point, as soon as you connect it, it backfires and stumbles and won't even move.

No vacuum leaks that we can find, it actually has steady vacuum when it idles, which is pretty much all it will do, unless you disconnect the advance.

Timing is on 8 BTDC and total is around 30. doesn't misss, just runs terrible, not fouling plugs either, checked and the dist is in right, firing order correct.

I feel like I'm looking right at the problem, but just don't see it.

What do you guys think ? We are stumped

 

Is this the same ignition set-up you were running prior to switching the intake and carburetor? If it is I would rule out a problem with the ignition box or distributor itself. I would be curious about whether the distributor was maybe off a tooth...
Is this a brand new carb or was it known to be good before?

Jay

 

It could be your crank pulley spun on the rubber, Take vac hose off dist. check vac with a guage at manifold and turn dist for max vac and then back off dist until vac drops down 2" on the gauge.Hook vac hose back to dist. Then try it if you are still having problems you can try ported vac to dist.

 

All the same stuff, just changed the manifold, ran great before.

 

You say vacuum is steady but what is it?
Where are you hooking the advance up to, what port?

 

Steady at 14 or so, on a manifold port

 

Do not have your answer. But, have a ZZ4 factory GM crate motor that comes with most everything including HEI distrib, except carb, etc. I had trouble from day one with it pinging on premium gas, correct timing, etc. Finally a guy suggested putting cap on distrib vacuum and carb outlet. Runs better than it has in years. Do not know why.

 

You are advancing the timing at idle if you have it hooked to MANIFOLD vacuum port.
Most common small block chevy set up is to run PORTED vacuum = no vacuum at idle. That would be the fitting just above the idle mixture screw on the passenger side front of the carb.
Try hooking it there, set your timing @ 10 deg. advance at idle.
good luck
Dave

 

You should have the distibutor advance connected to a ported vacuum. That is no vacuum at an idle and more vacuum as you raise the RPM. Not to manifold vacuum.
Alden

 

Ya, what Dave said. You don't want Vacuum at idle in the can. Go above the butterflys.
The Wizzard

 

yes... ported vacuum for vacuum advance