I saw another thread with someone that had the same problem, but I can't find it now.
Anyway, 302- compresion lowered to 10-1, Hydralic 3/4 race cam, Pertronics distributor, Holley 670 street advenger. 12 degrees timeing, 12 inches of steady vacume.Can't seem to get it to idle below 1100, hesitates and bogs down off idle, runs like a bear over 2000 rpm, I tried less timeing but that didn't help. Any ideas?

have you tried more timing? whats your total??? And are you running manifold vacuum?

More timing always makes everything better. ( as opposed to not enough:) )
it could give you a little more vacuum at idle...

A bog is usually a lean condition... that means you need to look into your mixture screws, and/or your acc pump cam.
If your pump sqiurts too slowly because of either bad adjustment, or a worn / the wrong cam, youll let too much air into the barrels just off idle...

I aggree. Big cam = low vacuum=high idle and needs more fuel from accel pump to jump.

Vacume leak?Intake gasket or carb base plate gasket? Would also make it lean.

The carb and the gasket are new, I checked for vacuum leaks,but I haven't tried adjusting the idle mixture yet. As far as the acc pump cam goes I don't think it's worn since it's new, but maybe because of the cam shaft I'm running I need a different acc cam. I guess I'll try to richen the idle mixture and try a little more timing and see what that does. Thanks everyone for helping me out on this.:beers:

Try pump cam in #2 setting if more initial timing fails using manifold vacuum on vacuum diaphram.

18 degrees initial timing, 36 degrees total timing, all in by 3000 rpm.
Blue pump cam, 35 squirter.


BTW, what are the specs on a 3/4 Race cam?

Wow, thats allot of timing! The manufacture specks say 4 degrees for the stock 302. I do have the vacuum booster connected to the manifold,( the booster is new), and the pvc valve hooked up to the carb in the back where it says to hook up the booster. I don't know the specks on the cam, Russ Hall Racing in Las Cruces,NM rebuilt the engine for me, all he told me was that it was the stock hydraulic 350hp cam for the 327. He called it a 3/4 race cam. I don't think it's that big of a cam where it would give me vacuum problems. I will try idle mixture tonight and see if that helps, also I'm going to disconnect the booster and plug the manifold port to eliminate a booster leak.

Does your cam have a lope to it at idle or is it stock smooth?

A cam with some hit to it needs alot of intial timing to be snappy. From the way you describe it coming alive above 2000 rpm tells me it needs more timing. Doesn't cost anything to set it to 18 inintial and try it.

The carb and the gasket are new, I checked for vacuum leaks,but I haven't tried adjusting the idle mixture yet. As far as the acc pump cam goes I don't think it's worn since it's new, but maybe because of the cam shaft I'm running I need a different acc cam. I guess I'll try to richen the idle mixture and try a little more timing and see what that does. Thanks everyone for helping me out on this.:beers:I don't think adjusting the idle mixture will help at all. Idle and acceleration are are different circuits in the carb.

Thanks, I will try a little more timing first, after I eliminate a booster leak.
Can't get to it until tonight, got a local car show this weekend that I'm entering the car in so I'm trying to get this solved before then.

I gave it some more timing and seemed to help, still won't idle below 1100, I have the curb idle screw all the way out.

Ben, I have 18 initial and 36 total degrees of timing all in by 2800 RPM. And another 15 degrees of vacuum advance at idle using full vacuum port on the carb. I have also up sized the jets to 72/76 in the stock 780 CFM Holley. This is with stock built 302, 11:1, Crane Blueprint 30-30. Long duration cams need a lot of initial. The factory had only 4 degrees of initial because that raised combustion temps for the smog system. The accelerator pump must be spot on adjustment so fuel squirts with the slightest movement.

I gave it some more timing and seemed to help, still won't idle below 1100, I have the curb idle screw all the way out.


Idle screws shouldn't have to be no more than 3/4 - 1.5 turns out off the seat. If they are turned way out, it's may be way too rich to run below 1100 rpm. Start off at 1 turn out and see what that does.

How much more timing did you try and was it set without the vacuum advance hooked up? Got to get the timing right before the carb will tune in.

The adjustment screw for the secondaries may be set too high causing it to idle off of them. Make sure of timing first.

The adjustment screw for the secondaries may be set too high causing it to idle off of them. Make sure of timing first.

Wrong..1st thing u do when set u a carb
Set secondaries because if they are not right, nothing will be right
Opposte side to throttle, under the edgw is a small stop screw for the secondaries
Get to it with a rivet with a hammered flatened end and a 90 DEG bend in it
Set the primary idle screw to middle factory spec
Set mixture screws to factory
now drop the secondary stop screw till the primary stuff works in a reasonable idle rpm range
DO NOT have the secondaries fully closed, they rest on the screw not the bores.

Now go to the accelerator pump, open throttle full, with your 2nd hand make sure u can still push the carb accelerator pump up, and measure and adjust with your 3rd hand the pump so it has about 18 to 20 /1000 play

Get these right and u can now start to play with timing, vaccuum settings and such