Hi all,

Sorry, but Ive got some more carb questions...  I apologize for continuing to beg for help!

So here is the essence:

Car is a 56 sunliner, 292, ford-o, blue thunder intake, and mummert 270 cam, with 224 duration at .050.  (I mention that since it seems from what Ive read that this is a cutoff on some carbs - i.e. street demon 525 says for cams under 220 deg...)  Engine is healthy - compression was even when last checked (last year), new cap, plugs, wires.  Also has pertronix on a 57 dizzy.

Ive been working with 2 carbs - an edelbrock 500 and a holley 390.  Holley starts easier and has better throttle response (but still has some stumbling and spit back through carb at some points), but edelbrock runs better at wot (as would be expected with more cfm).

1)  Edelbrock carb pulls 11.5 in hg at idle, Holley pulls 7.5 at same RPM.  Does this make sense?  Not sure what this tells me or means, or if "thats just the way it is"

2)  I have been told to check the idle transfer slot on the Holley to make sure that I dont need to drill a small hole in the primary plates.  The transfer slots are covered... but JUST barely.  the throttle blades measure .065" thick, but the most they cover the transfer slot is .028".... just barely... is this enough, or would the hole in the blades help?  I dont want to drill them and have it be wrong... what are the consequences?  I do know that the idle screws dont have a lot of impact on the vaccuum... meaning that it takes a fair bit of adjustment to see a difference.

Right now the holley has 56 primary jets, 62 secondary jets, 3.5 power valve, and a 25 shooter.  Not sure if anything seems out of whack on that or if anyone has any recommendations?

Does any of this make sense?  I am getting really frustrated with trying to get a carb (ANY carb!) to run what I would consider right - easy starts, pulls evenly, without bogs or stumbles, with decent throttle response/mileage (is that oo much to ask???)  I think I wnat to try to get the holley dialed in first, as I dont drag race the thing, and the holley seems easiest to tune/adjust for me to learn on.

Please let me know if there is any more info that would help, or if anyone has any ideas/observations/different starting points?  Im really starting to regret the cam choice!

Ron Grove

Wauconda, IL

Well just a first thouught about your carb question. If the Edelbrock can produce 11.5 inches of vacume and the Holley only 7.5 then check for a vacuum leak with the Holley. The throttle plates size should be very similar on both carbs and that big of a difference should be investigated and resolved. And by the way, you have TOO MUCH CAM for a car with FOM (only my opinion). Work on trying to increase manifold vaccum. Think of a 4BBL carb as a two BBL UNTIL you have high flow low manifold vaccum and the back 2 BBL open. So at idle you are dealing with a 250 CFM carb and all is not well. Is the cam timing correct or could it be too retarded?

Sounds like a lean condition on the holley, the power valve 3.5 seems abit too small. I would try going to a 6.5 to see if that will put a stop to the spitting and keep the accelerating smooth. I believe the original power valve was a 6.5 or 7.5. While the carb is off check to make sure the screws that hold the base plate on are tight to ward off any vacuum leaks etcs. If you are only pulling 7 or so inches of vacuum keep the power lower.Good luck and keep us informed on how it's going.

-Gary Burnette-

If the idle transfer slots in the Holley are almost covered, then additional bypass or holes in the throttle blades are not needed.  In fact, putting the holes in the blades at this point will add to any stumbling or hesitation issues the carb may or may not already have.  Recheck the secondary throttle blades in that they are seating closed and are both uniform in their closure.  As Pete suggests, sounds like a vacuum leak with the Holley.  Recheck the gasket flange crossways on the Holley with a straight edge.

Lorena, Texas (South of Waco)

Thanks for the great replies! 

I guess i never thought of the holley having a problem....I got it new, and it never occured to me there might be an issue.  I couldnt for the life of me figure out a logical reason why the vaccuum would be so dirfferent, and I guess there isnt one!
I will check the straightness of the bottom, and make sure all the bolts are tight before I put it back on, use a new gasket, and if it doesnt pull close to the same vaccuum, ill break out the carb cleaner spray to see if I can find a leak!

Also, do you guys really think its too much cam?  I talked to John Mummert, and he thought that this would be ok when I bought the cam... a little lopey idle, a little more power, but still useable/streetable w/ a fordo.  Thoughts?

I cant thank you all enough for the help.

Ron Grove

Wauconda, IL

That is not too much cam for your application, I'm putting a larger one in my 56 merc built 312 with the automatic. A 224 @ 50 cam with a running duration of 270 is a mild cam, excellent for the street with very good perfomance and still far better than stock. Should perform nicely on the strip as well.

-Gary Burnette-

Hey Gary,

Is that a Comp Cams item?  I know you have said you have had good luck with them.  Is that grind similar to an Isky RPM300?

Paul J. - '57 E Code

OK you love your cam. What kind of vacuum are you showing at idle in neutral andv also in drive? When you go from park to drive what RPM are you showing? Enquireing minds want to know.

Are you asking me?

Ron Grove

Wauconda, IL

I'ts obvious that the cam is not the problem. One carb ( edelbrock ) pulls 11.5 in hg which sounds about right. The holley is only pulling 7.5 in hg which is on the low side and saying a possible vacuum leak somewhere from the carb?

-Gary Burnette-