Stumble Right After Car Grabs 2nd Gear

[BanditRich]

Cliff when I talked to you on the phone after my mechanic replaced the cracked airhorn with the one you sent me along with the blown acc pump with a new one from your HP kit you told me now that my car is putting down the power it is supposed to the fuel pump isn't keeping up causing this to happen. So I'm planning to get a new one and replace the lines too. I was reading in your book how if the checkball doesn't have a good seat it won't keep fuel present all the way to the discharge holes in the airhorn. You also said if the checkball retainer isn't sealing good it adversely affects performance.
Before my mechanic replaced the airhorn and accelerator pump the airhorn gasket was always wet and the car reaked of gas. It also lagged bigtime before the car grabbed 2nd gear even though the secondary air valve spring was at 1/2 turn.
Now it plants and takes off the way it should only issue is this momentary stumble and the power comes railroading right back.
My mechanic didn't touch the checkball or the retainer he just replaced the accelerator pump. This stumble has only been since after I got the car back; so it shouldn't be an issue with the checkball or the retainer, right?

[BanditRich]

^ Upon further reading seeing how my carb is set up following the 1st recipe - the engine is pushing out around 300 hp - the old airhorn had the accelerator pump discharge holes drilled out to .028; I didn't have my mechanic check them on the new airhorn so I know they are whatever the stock size is. Could this be causing this too; or is it just needing a new fuel pump?

[BanditRich]

Also, I don't have the vent& purge lines from the carb hooked up to the charcoal canister- nothing's hooked up to it but I left it there because it would be obvious something belonged in that spot. Would hooking those lines up alleviate this hesitation?

[Cliff Ruggles]

A leak at the checkball or retainer will only cause the fuel on the delivery side of the pump to drain down a bit.  This causes a momentary delay in delivery when the pump moves down quickly to avoid a lean condition.

This would be felt as a momentary hesitation when you depress the throttle quickly, probably wouldn't even show up for "normal" driving/light throttle acceleration......Cliff

[BanditRich]

Well it's definitely not a checkball / retainer issue there's no hesitation when I hit the gas from a stop or if I'm driving along & hit it. It's right after it grabs the next gear.
I hooked up the bowl vent line from the carb to the charcoal canister but didn't have time to hook up the purge line or the vacuum line that hooks up to the tree on the back of the carb. I think I'm on the right track - the hesitation is still there but it's a LOT less.
My car is now at its winter home for hibernation. When it comes out in the Spring it will be getting a new fuel pump & lines and I will be hooking up the other lines to the charcoal canister. Seeing how there was an improvement with this issue just hooking up the vent line I think that after the other lines are in place along with a new fuel pump & fuel lines it will be all set.

[BanditRich]

On a related note, now that I have APT access which way do I turn the screw over the top to add more fuel?

[Frank400]

If it's the APT that you access from the top of the air horn (later carbs), clockwise = leaner, and counterclockwise = richer

[Cliff Ruggles]

APT is used to tune part throttle A/F or for "normal" driving when the vacuum is high and Power Piston is down.  CCW adds fuel, CW leans it up.

If you floor it and no problems till you hit second gear then it's fuel delivery related, not a carb problem......Cliff

[BanditRich]

OK thanks Cliff apparently the APT doesn't need to be fine - tuned. I'll let you know how she goes in the Spring after the new fuel pump & all the lines are hooked up. Also she's getting a new distributor & spark plugs.