hello guys... my buddy was over the other day... he brought his timing light...i checked the timing with the vac advance plugged into manifold vacuum......it showed me 36 degrees of timing.......is this correct for idle????? when i disconect the vac advance.. the car runs rough...... any ideas.....

should i hook the vac advance up to manifold vac or ...times vac...

if i leave the vac advance on manifold... is 36 degrees too much for idle...??

i just installed a curve kit also...



Rob

 

You should check the base timing with vacuum advance disconnected and the hole plugged. You should also run the vacuum advance from a ported source not from the manifold. This will give no advance at idle.

 

thanx...tonight i tried pulling the vac line ..and putting it on ported vac... the car didnt want to run....but ..thinking of it now ..i will problebly have to set the carb up again....because it was set up with timing advanced.............

the vac advance problebly runs about what 20-24 degrees advance?? so by putting the vac advance on port.. i'm getting about 14degrees at idle ...right?

i believe on the q jet the port on the pass side front is ported correct ??

thanx...


rob

 

Yeah that looks about right 10 - 14. Should have 34 -36 in by 2800 - 3000 RPM.

 

cool... ill work on it tomarrow.....

thanx

 

I don't think you'll get that much from vacuum advance...maybe more like 12-14 degrees.

The majority of GM engines always used ported/timed vacuum for advance, I think I remember some that used intake vacuum, but it's definitely more common to use ported/timed advance, as well as easier to tune.

Disconnect the vacuum advance to check it for "all in".

Easy way to tell if the port is intake or timed is to just remove the hose and place your finger over it...assuming the throttle blades are closed, if you have vacuum, then it's intake port, not vac until the blades open...it's timed/ported vac.

 

There's an article about all this on this site's tech articles section. It's for GM HEI ignitions but everything it says about recurving the centrifugal and vacuum advance mechnaisms applies to any distributor.