I have a 69 Hemi roadrunner I got 50 years ago and, in the process of restoring it, I took the carbs over to Harms (great job), new lines, new tank, and ended up with apparently a faulty fuel pump, the original one. Found a similar model and installed it. Now, if the car
It's not started for 2-3 days i have to put some fuel in the intake, otherwise it won't start. Is it possible that the new pump is not as good as advertised? The all point is: does anybody know if there is a place to have the original pump rebuilt or who sells the kit to do it, probably easy enough. Help! Thank you. PS: unless is the new gas that does that......

most likely you have a fuel evaporation problem. it's easy to test the pump for pressure. don't buy the mancini rebuild kit; it's junk. you may look at taking the guts out of the new pump and putting them in the old pump. IIRC only the top section of the pumps have any numbers on them. they're fairly easy to take apart and work on.

before you start it see if the accel pump kicks out a good squirt

Yes they can be rebuilt, I have done them. Kits available. Most likely evap is the issue. I have that problem with mine as do others I know. An electric fuel pump for priming before start is a good solution.

What carburetors do you have?

Two Carter afb

As some of the others have mentioned, you have a fuel starvation issue.

I'm messing with project now and am having the same issue with the same carburetor (single carburetor in my case that is a fresh rebuild, ignition timing is spot-on). I had previously read about difficult starting problems with these carburetors after the engine sits for a day or more. Evaporation and drain-back were the 2 main causes I had read about but both seemed to be best-guesses as to what was actually happening. I thought I'd go after the easiest of the 2 causes to address and added a fuel flow check-valve in-line on mine and that seemed to cut the problem in half or better. After sitting for a week or so, my truck started a lot easier bit it still isn't a "normal start-up" like you have with a warm engine. I normally crank for 10-15 seconds, stop and pump the throttle 2 or 3 times, and re-crank for another 10-15 seconds. Previously this same technique took me 8-10 cranking / pump cycles. Yesterday it took 3 cycles. Perhaps it would be even better if I had an even better quality check valve (I'm guessing mine is not 100% checking back-flow).

- EM

with fuel evaporating in the bowls thru the vents it's impossible for any drain back or siphon. the real issue is alcohol and the fuel boiling around 130f. heat spacers delay the evaporation a little but there really isn't a cure. carter afb's get a lot of blame but holleys are just as bad. it's nothing to do with carb brand. when my cars sit a few days or week or so I just fill the bowls with a squirt bottle and start up is instant. some folks use an electric pump to refill the bowls. that's ok but the pumps you buy today have to stay running because the mech pumps won't pull thru the modern vane pumps. a mech pump can pull thru an old diaphragm electric pump. I've just learned to live with it and jump thru the filling the bowls thing during prolonged engine sitting.

The addition of the check valve in my fuel line and the results thereafter proved there was in fact a drain back problem. I don't have a heat evaporation problem given the engine has never run for more than 10 minutes at this point and the carburetor is about 10" from the manifold.

- EM

it's impossible to drain the carb. once the needle relaxes from the seat there's no way fuel will drain back. residual fuel in the line may drain back thru the pump valves but thats it.

Re drainback vs evaporating, could be both. Fuel in the carb is likely evaporating and bad valves in the pump are allowing drainback of the lines.

Drainback is a problem even with new mechanical pumps. To check, rig a see through filter just upstream and above the pump. Check the filter every half hour after shutdown until cool and again before restarting the engine. I had a CJ5 that had hard start problems and confirmed drainback as the problem when the filter would go dry in less than 2 minutes. My Roadrunner would drainback overnight.