I've got a 70 T/A Challenger with a original 340/6pack, I rarely drive it anymore , but I fired it up the other day and noticed the accelerator pump is leaking pretty bad! So it looks like I will pull the carbs ,anyway I need to know what size diaphragm it has ! E-bay has both 50 cc and 30 cc, anybody know which one I need?
Thanks!

From pictures I see on line it is the small Accelerator pump

common would be the 30cc.
I added the 50cc to my carb once. it noticably is larger and hangs down farther.

Thanks guys!

center carb came with 30cc pump. may not be the pump but a poor seal between the metering block and carb body due to warpage. been thru it!

The original 30 CC pump diaphragms are black in color and don't last long with todays fuel, I would replace it with one the newer green ones that will last with alcohol

Cab is the man! (& for your app I wouldn't think you'd need the extra squirt from 50CC's)

Pull the carb off, remove the pump cover, and using some fine sandpaper on a flat surface (like a pane of glass), sand the mounting flange. I'll bet it's warped. Then use the green diaphragm like Cab advised. Set the lever so that at full throttle there's .050 clearance between the lever and the adjustment screw that pushes on it. Lever should move immediately when throttle is cracked open. Fine-tune adjustment if/as necessary for that.

^^^ good info (& sand in a figure 8). EDIT with solvent & not sure what grit paper, 600?

There is not enough clearance for 50cc pump on a six pack.

Can't speak for a 340, but plenty of room on a 440 6 pack.
Ours is not a race only and the 50 cc was a bit to rich on tip-in.
Went back to a 30 cc with no reduction in crispness.
And yes, get the green ones from Holley.
Joe

50 cc itself goes not pump any more fuel than a 30 cc. The pump cam dictates total squirt volume. If you use either of the two largest pump cams, you have to use the 50 cc pump or you will bottom out the 30 cc pump diaphram.

is it gonna warp after 20 years? I built the car in 1992 and have never had a problem, just recently ,it's been a year since I last ran it and the leak developed!

Green one ordered 30 cc! Thanks!

what happens is the body gets distorted from repeated tightening of the float bowl screws. if your carb has had few rebuilds/jet changes/etc then maybe your ok. I know I've chased accelerator pump leaks only to find the weeping was between the metering block and carb body.

Murphy loves messing with us hot rodders My message is many things, problems, can have the same results cause by several different things

i have a 50cc pump on my six pack, plenty of room

Many people think that when they hear 50 CC pump they think it will squirt 50CC Not in one squirt and the pump will not hold 50 CC either, Holley rates their pump volume in 10 shots so a 30 CC pump is SUPPOSE to squirt 30 CC in ten pumps, not one pump
so that means it SHOULD pump 3.0 CC per pump shot
5.0 CC shot volume for the 50 CC pumps for one pump squirt also, if it is adjusted properly

Only if you have the cams to support the 3 and 5 cc lever depression. All of the cams are rated for total squirt volume (per 10 squirts as Cab says)

I've also had 2 or 3 diagrams start leaking where the little metal disk for the lever to ride on penetrates the rubber diaphragm. FWIW.