Paul: I'd suggest spending 10$ and getting Dons carb tuning guide at www.4secondsflat.com . It's primarily for demon carbs, but it'll apply to the holley HP's as well, as they are so similar. It might help clear up some issues for you, as it helped me with mine... It's the best $10 I've spent on my build so far!
Good luck, wish I could offer more advice...
ed

 

Change the power valve to a 2.5

 

I changed the power valve it didn't run any better. I put the 5.0 valves back in and with the throttle blades full closed I was able to get the idle to run at 900 RPM. Maximum vaccum ( 13-14") was obtained with the idle screws turned down to 1/2 a turn out from full closed. Is acceptable to run the idle closed down that much?

 

Maybe , but I am surprised it will idle at all with the screws turned in that much . Which with a Holley usually means you have some air/fuel leakage from the primary circuit or you are idleing off your primary circuit or you have a power valve issue , maybe the gasket behind the power valve ? . Try closing the primary blades down more , turn the screws out 3 or 4 turns and start over. Try changing the gasket between the body and the idle plate as this is sometimes a problem with mating surface flatness. Most Carb tuners will mill the body face to improve the surface flatness.
With that much idle vac that 5.0 valve should work. I use a vacumn gage when I adjust the idle circuit and try to peak the vac signal using the idle screws , try that after you do the above .

 

I ended up with the primary throttle blades fully closed and the idle fuel screws only ½ turn out. Also I have a 6.5 power valve ( I though I had a 5 ) which works with 14” of vacuum. Also if I do a vary rapid stop, the engine will stumble and if I stop hard enough it will die. The Holley tech rep recommended that I drop the rear float level a bit and open the primary throttle blades a small amount and richen up the primary idle screws. Any thoughts? I‘ll replace the gasket and see if that helps. Thanks.

 

Are you saying that you are setting idle speed with the air screws? It sounded like that in your first post.

Bill G

 

Well sort of. I first set the idle with the throttle butterflies and all four idle fuel screws at 1 ½ turns out. Then using the vacuum gage, I adjust each idle fuel screw until the maximum vacuum is obtained, working one idle fuel screw at a time, also adjusting the throttle butterflies to maintain idle speed. I go around the four idle fuel screws a couple of times until there is no change in vacuum or idle speed.

 

Paul,

I have the Ford 392 stroker in my roadster (430 HP version). I first used the Holley carb you have now. Had the carb tune on the dyno at JBA Racing in San Diego a few months back. They couldn't jet the primaries down far enough, period. They even pulled the choke horn to get more air flow. On the dyno, the motor ran out of carb above 4 grand (pulling over 2" of vacuum at 6 grand).

The solution was an 850 cfm BG Mighty Demon. Just ran at Willow Springs Raceway all weekend (Western Roundup) and the car never ran so strong .

And I only did a minor adjustment on the idle circuits and I was off.

My 2 cents .

Dave Lowen

 

Paul,

Regardless of what you have read online to date, your over carb'd.......You really want to wake up that 392 stroker, get yourself a Holley 650dp, part number 04777C, then book some quality chassis dyno time. It really is that simple.........


Bill S.

 

As for being over carburetored,I really don't think so, the motor runs great at any rpm except idle. Great throttle response and a real screamer when I kick in the second two barrels. I’m sure the 650 would provide better low speed torque, but the 750 works great and is a real kick at mid to top end.

 

One guy claims he's over carbed, and the other undercarbed. Man, you guys make this confusing.

I have the same setup, and am hoping it runs good.

 

I have a 4150 HP750 on my 11:1 351W. big heads and compression are forgiving for the larger carb but it is jetted at 78/86 on the dyno w/peakHP at 6200.
Despite the big carb/jets it idles just fine, very snappy jump on the throttle, no hesitation or surges. Do you have adjustable air bleeds ?? If you do they are the eight small jet like orifices 4front/4rear on the throttle body. The OUTER FOUR are idle air bleeds. Carefully remove them and/or check the size w/mag glass. The # is stamped on top. Jumping up four sizes all around (ie: .0032 to.0036) will allow much more air in BELOW the venturis where the extra air will not also pull more fuel. You can call Holley tech line for more help on that. Also,on their website there are tuning manuals that can be down loaded . They should also address a small screw beneath the carb inside and under the secondary lever. I think slight adjustment to this (see the manual)will crack the secs very slightly again allowing more air flow at idle . Just cracking the secs slightly cured my stall/stumble on hard starts when I had a 650BG Race Demon on the same motor.