I am new to Mopar. Recently purchased a 1974 Duster with slant 6 engine. 49,000 original miles and I bought it from the original owner! I love the car. I replaced a few items, coil, carburetor (Holley 1945), rotor, cap, wires, alternator, voltage regulator, belts, ps hoses, heater core, and all the hoses. When cold, I give the throttle one pump, release and start her up. She always fires up immediately. However, when I take drives (short or long) the engine can be difficult to start. I really have to pump the throttle while starting for it to catch. I've set the timing as indicated to TDC, and have the idle set a bit higher than suggested in the manual (around 850 RPM). I set up the carb myself--got the engine warm and screwed IN the needle until it started to run really lean. I backed out the needle until I achieved the highest RPM. Any suggestions? Car runs great otherwise. A bit short on power, but still very fun!

Pumping the gas while trying to start a warm engine makes it harder to start. It's hard to start because it's flooded; pumping adds more gasoline, which is the opposite of what you want. Next time it acts up, push the accelerator to the floor and hold it there (no pumping) while you crank the engine. Once the engine catches and runs, release the accelerator.

The problem is caused by heat in combination with the characteristics of today's gasoline vs. the stuff these cars were designed to run on. Do the Fuel line mod and make and add a carburetor heat shield. Make sure the manifold heat control valve is working correctly and isn't stuck.

If you replaced the carburetor, it's a fairly good bet you replaced it with a "remanufactured" item from a parts store (local or online). "Remanufactured" parts, including carburetors, are junk. Hope you kept the original!

Tune-up parts and technique suggestions in this thread. Read them even if you think "But I already did a tune-up!"; pay careful attention to the info on spark plugs and spark plug washers.

Set the timing to 5° Before Top Dead Center (engine idling at 750 to 800 rpm, vacuum advance hose disconnected from distributor and plugged). Speaking of the vacuum advance hose: see that it runs directly from the carburetor to the distributor. If it runs from the carburetor to a widget on the side of the air cleaner housing and from there to the distributor, bypass the widget (OSAC valve, primitive emission control device that spoils driveability and fuel economy) so the hose runs directly from carburetor to distributor.

Your idle adjustment procedure is almost kinda close, sorta, but isn't the right way to do it. Carburetor operation and repair manuals and links to training movies and carb repair/modification threads (including info on how to adjust the idle) are posted here. Keep on top of the valve adjustment

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Thanks Mr. Dan. I've noticed (here and at FABO) that you are a venerated expert on the slant 6! I'll try the method for starting hot you suggested and look into the other things too. My vacuum advance hose runs directly to the carb. Should I disconnect all the other vacuum hoses? The car is stock and everything is hooked up as original as far as I can tell--I'll try to add a photo. Also, I do have the original carb. I would have rebuilt that one, but the inlet threads were completely stripped and since this is where the float sits I wasn't sure it could be repaired. The remanufactured carb seems to work quite well. Thank you again for your help. I enjoy your posts and have learned much about this engine from them.

No, leave them in place.
Ah, ouch. Yeah, that pretty much necessitates a replacement.
Odds are against that lasting.
Glad to help out.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.