Carb tuning question

scr11 · #1 (**permalink**) 07-13-2002, 07:44 PM

I have a Holley HP series 750 DP on my 393 stroker. I was checking a few things today and I noticed that my 4 corner idle mixture screws are all at different settings. What's odd is that I had a wide band test done two months back and we had a perfect 13:1 air/fuel ratio. Anyway, here's what I found today:
Front driver's side screw was 1.5 turns out.
Front passenger side screw was 2 turns out.
Rear driver's side screw was 2 turns out.
Rear passenger side screw was 1.25 turns out.
I would think that all screws would need to set at the same number of turns, or maybe at least the two front screws would be the same, or the rear two screws would be the same.
Does any of this really matter?
Thanks
Scott, SPF#1230

kountzecobra · #2 (**permalink**) 07-13-2002, 09:00 PM

Scott, I wouldn't worry about it. In my experience they are hardly ever exactly the same, but they are usually within one turn, or so, of each other. If you want to fool with it, you can hook up a vacuum gauge to manifold vacuum and tweek the primary adjustment screws to the highest vacuum reading at idle. But it may not be any improvement. Mess with it a little- you may help it. 13:1 is a tad on the rich side, but safe. Damn, aren't these cars fun? Also, how was Houston bunch meeting? We had 3.25" rain today. Cobra has to stay in this weekend. Later, David Shelton.

Rick Parker · #3 (**permalink**) 07-13-2002, 10:49 PM

Scott:
As Dave has said they usually aren't the same however if you do attempt to adjust them, adjust the front two as a pair; meaning adjust them together striving for the highest rpm THEN adjust the rear pair doing the same thing. Avoid adjusting the front & rear on one side and then the front & rear on the other side.

Good luck
Rick

scr11 · #4 (**permalink**) 07-14-2002, 07:34 AM

Thanks guys. I may hook up the vacuum gauge and see if anything is outta line. It shouldn't be, but hey, you never know.

scr11 · #5 (**permalink**) 07-14-2002, 07:40 AM

David - The monthly meet was a good time. We had fewer cars this time as a few folks couldn't make it and of course, the chance of showers didn't help things. We had about 15 people or so for lunch.
Craig had a good idea of setting up a morning cruise sometime soon. Seeing as this is the hottest time of year, it sounds like a good idea to me. Maybe we can get 5 or 6 cars together (or more) to go for a short cruise somewhere that offers a few nice turns and little traffic. I'll start a thread next week and ask folks to offer some suggestions.
Hope to see your car soon!

Scott, SPF#1230