I have had some serious carb issues lately, yesterday with the help of Mr.Pbody and DC426, I was able to get it running much better. I made some whole sale changes and fattened the heck out of it. I test drove it, and all seemed pretty good, a little lazy, but the original problem of the flat spot was just about nil. Take it out this morning to have DC help with some fine tuning and it's much better, not nearly as rich as it was, and it's much more crisp and responsive.

The run down of what we did is:
Lowered the fuel pressure from 7.75 to 7 psi.

lowered the primary jetting down to 84 primary and 92 in the secondary. With a 3.5 PV.

Synchronized the idle mixture screws. (I had them all jacked up).

Lowered the idle about 100 RPM, it now idles at about 1050 in neutral and 950 in gear.

It was still just a tad lazy on the rev, so we adjust the pump arm and tried a 42 squirter, for whatever reason, it didnt like that; changed the idle characteristics, so we went back to the 35.

So now it's about as crisp as it ever was, very good idle quality in and out of gear, but the flat spot has shown up again. Not really bad but I had to feather the throttle just a touch to get through it. The ONLY time it has it is when loaded in high gear. I only notice it if I'm cruising and have to get out of the throttle for a car in front of me, then roll back into it. When it does that I can roll back out of the throttle and give it a little pump shot and all is fine. Like I said all characteristics are good, idle, cruise and WOT, just that little hesitation or flat spot. If I could just figure that out I'd be a happy camper. Just fishing here to see if anybody had some ideas.

Thanks,
John

What number my 9375 only likes 25 to 28 squirters??

It is a QFT 1050

Timing is at 38 and is locked.

have you tried bigger squirters? don't see the advantage of lowering the fuel pressure. that maybe ok at low rpm but I bet you run out of fuel on the big end. just went through that. took 9.5 pounds of fuel pressure to run all the way through the 1/4 without running out of fuel.

We'll have to wait and see on the fuel pressure Tony, but thats good food for thought. We did try a bigger squirter, but not on a test drive, we tried a 42 and for whatever reason it acted funny just sitting there so we went back to the original.

I'm not sweating it like I was before when I just could not get the thing to run well at all. I may be asking too much, the flat spot is not affecting the range of operation, the cruise is nice, accelerates in stop and go driving just fine and wide open is great (for short duration). I could actually live with it as is, just thought I throw it out there if anybody had some ideas. I can say this is the best it has ever been, I used to fight the flat spot while in cruise, so I know it's better.

Thats a thought Mike, I know we adjusted it, I may have had too much slack in it and DC tightened it up, I'll take another look at it.

Have you adjusted both accelerator pump arms so there is no freeplay between the pump arm and the pump lever? Most of the Holley carbs I've seen have slop bewteen the pump arm amd the lever Holley tech says to adjust the screw on the pump lever so it has .015 or a little more travel(clearance between the lever and the bottom of the screw with a feeler gauge) when at WOT. That ends up putting tension on the adjuster so it pumps immieditily (SP?) whenever the throttle is moved

If the pump arms are set correctly i would be looking @ mixture screws , a slight bog @ tip in coming back on the throttle is a lean spot between idle/transition , turn all four mixture screws out 1/4 turn & go try it.

What size Idle air bleeds does it have in it?

I had to change the idle fuel restrictions, idle air bleeds and transfer slot jets around in mine untill I got it to work right at part throttle and in transition.

If it's a 3 circut carb richen the intermediate air bleed.

Bob, I think it's still an idle circuit issue. The problem arises when he cruising and lets off the throttle. Then steps back on the throttle and it hesitates. John hasn't said but I don't think it's doing it from a stop. It also didn't do it before we made adjustments earlier today. I think it's just an air screw adjustment.
DC