I have a small surging problem when I am running at a steady speed & I can't figure it out.

My car is 66 coupe, 93 Cobra shortblock, running a new Holley 570 Street Avenger on an old Edelbrock F4B intake.
I have new Summit dizzy (without points), new wires & new plugs.
I have set the carb a few times following Holleys instructions, floats & mixture & I think it's right.
Acceleration & starting are fine, just a slight surging when a steady speed & it's annoying.
Timing is at 12 now (I've tried from 5 to 14 with same effects, lack of power at 5 & a little pinging at 14).

My fuel pump went out a while back & I put on a new Holley mech 110. Holley says that doesn't require a regulator but is it possible it is to big & maybe a little too much fuel pressure?
Fuel filter is also new. New Optima yellow top battery also.

What can I check now? I'm out of ideas.

 

the bottom line is that the primary jets in a 570 are TINY, too small for even a stock 289/302. i can say that confidently because i have a stock 289 and i was having the very same surge you are describing while cruising. i had tweaked the carb every which way i could think other than messing with jets.

went from a size 54 primary jet to a size 58...she runs smooth as butter now. GL

 

Thanks, I'll give that a shot.
What size is anybody else with a 570 running?

 

i'm on the same opinion and my first instinct as well when I heard that combo and carb.
I run the 570 with 302 with eldelbrock heads, intake, cam

54 jets is way too lean for my combo as well. since you say you get this hesitation at constant speeds (lets say 50mph constant in 4th) the first thing I'd do as well is to jet up. I run the same carb. It's not the wrong for the car, it's just jetted awkwardly lean

i run 58 or 60 jets at the moment (forgot).
Change the primary jets to 60, if it cures the problem try 58

Kalli

 

Try going up 2 sizes on both the front and the rear. If it gets better but the problem is still there, then go up another 2 sizes front and rear. Just make sure you jet the rear up the same amount as the front, firstly because if the primaries are lean, so are the secondaries, and secondly, you need to keep the jetting balanced so you don't run too lean on the front or back cylinders and/or too rich on the front/back cylinders. I had the same problem with mine...some carbs come rich, some come lean.

 

I took the 54 jets out & put in a pair of 60's today.
Surging is gone. Stumble is gone & overall performance is MUCH better.
I guess I'll be using a little more gas now, but if I wanted good mileage I wouldn't have this car anyway!

Thanks jonward786 & kalli!!!!!!!!