View Full Version : Big heads and cam no vacuume

01-22-2007, 06:59 PM
I have an x drag car small block, 400 block 3.50 crank Dart 230 cylinder heads 13.5 compression, big roller cam, Holley 750 carb 4 corner idle with power valve blocked off 71 jets in front 80's in back ,620 lift automatic trans with a big converter. The engine was together when I purchased it. The problem; It's too rich idling an fouls plugs. I've tried a carb with a power valve (2.5) and it did not really help. The manifold vacuum is only about 3.5 when in gear at idle. I've had cars with bigger cams and not had this problem any suggestions or quick fix or band-aids ??? thanks, Mark

01-23-2007, 09:36 AM
Most likely with that combo you have the throttleblades opened too far up the transfer slot and you no longer have control over the idle circurt.

Are there any by-pass air holes in the throttleplates?

Also I think your main system seems under jetted for a 13:1 combo with a set of 230 Darts.

How much vac in park and what's your RPM?

01-23-2007, 11:14 AM
OK, the carb is a 950 HP with out vacuume ports and without ajustable air bleeds part no. 80496. Sorry for the mis-information. Yes there are holes in the blades and the idle is about 1200 rpm the vacuume is about 3. The timming is about 18 initial and 36 total. mark

01-23-2007, 04:02 PM
Thanks for the info:

The HP series carbs consist of an assortment of mis-matched components for street use and were intended for circle track appiclations.

I recalabrate HP carbs on a regular basis and there is no "Quick fix" for this carb as almost every aspect of this unit is out of balance....

Metering blocks = Idle feed restriction (IFR) is too large and has been located in a poor position, the results is poor tuning responce....also some units have more emulsion holes than needed.

HP950 mainbody= small venturi (750) and uses the large 850 downleg boosters with a .180" passage which again contributes to it's lack of balance....stock 750 has a .140" passage.

Baseplate= no vacuum ports for tuning or accessories and overly large by-pass air holes of 5/32"

If you like, package it up and send it to me to recal.