: holley 750DP flat spot
Sep 30th, 00, 07:06 AM
I installed a new AED Holley 750DP on my 69 Z/28 and I now have a slight hesitation when I give it a little gas from a constant speed, if I jump on it it's fine. The current jetting is 70/78, squirter size is .031/.035.
302cid, 9.7-1 comp., world casting S/R torquer 2.02/1.60 pocket ported gasket matched , weiand stealth intake, comp cam CS272TL-6 242int/246ex duration @.050 .510int/.519ex lift @ 1.5 rocker (it now has 1.6 roller rockers so I don't know how much the lift has been increased), stock points distributor, timing is set @ 12 BTDC.
Sep 30th, 00, 02:49 PM
My guess is either accelerator pump or power valve. The easy one is the pump,and I will tell you how I set the pump and it's not how Holley says to do but it always works for me.The screw on the pump arm with the spring on it,tighten it to make it shorter until there is slack between it and the pump arm,then loosen the screw until it just touches again or zero clerance,then loosen it about another 1/2 or 3/4 turn to preload it.If you do this and still have same problem get the pack of Holley pump cams and change the pump cam,start with the blue,and reset the pump arm as before.
If this don't help post what happened.
Mark W. Winning
Oct 2nd, 00, 03:33 AM
I would have to agree and lean towards the power valve. The DP is a fairly easy carb to get atleast close with.
1992 Firebird 355/Six Speed
1991 RS 350 / 700-R4
1987 Toyota Pickup 383 / 500 + HP 10.963 @ 119.95 Slicks / 11.997 @ 114.23 Radials
Oct 4th, 00, 07:13 PM
I finally received the Holley carb cam kit from Summit today. I tried the blue cam and it runs 100% better, but the screw bottoms out before there is any slack. I even inserted the screw in the bottom hole and could not get the adjustment right. I will compare the blue cam profile with the others and see if I can get the same profile with a mounting hole that would place the cam lower on the throttle shaft allowing for the correct adjustment.
Regarding the power valve, I blew one on another car 25 years ago and from what I remember the thing wouldn't idle or run at a constant speed it would only accelerate.
My camaro runs fine it just had a slight hesitation when I gave it a little gas. No problem when I jumpped on it, in fact last weekend I blew away a new Porsche Cabriolet Carrera 2 the guy was so pissed he had to race me again, and I blew his doors off a second time and I never took it past 6000!!
Thanks for your help.
Oct 5th, 00, 07:19 PM
Thanks for the reply,its good to here when some one gets their ride running better.Good story on the Porche.
If you are having any stumble in the secondaries, which I don't think you are but since you have the pump cams use the red on the rear if you need it.
Oct 6th, 00, 10:42 AM
Scott, good to hear you dialed most of it out with accel. PV would also help. If you had a vacuum guage you could see exactly where this occurs. I ran a 10.5 in a lopey 427. No flat spots at all. Milage sucked though. Went to an 8.5. Point is that a 085/095/105 PV will enrich things and give you a nicer midrange transition.
67 Chevelle SS 427/L88 (http://www.chevelles.com/showroom/chaas00.jpg)
Oct 6th, 00, 06:51 PM
Just a reminder, you DID check the float levels first, right?
Check my web page for First Gen Camaro suspension info:
David's Motorsports page (http://ourworld.compuserve.com/homepages/David_Pozzi/)
First Gen Suspension Page (http://ourworld.compuserve.com/homepages/David_Pozzi/first_gen_suspension.htm)
67 RS 327
69 Camaro Vintage Racer
65 Lola T-70 Can Am Vintage Racer