Rough Start
 

I have a 73 C3 with a Quadrajet. I rebuilt the carb and it had been starting and running fine. One Saturday it did not want to start. Since then it starts rough with a slight miss then smooths out after a minute. Runs great from there. After turning off the motor when warm it does not want to restart and feels like it is flooded. Misses terribly then smooths out again. New plugs, new wires, rotor, cap, points, etc. Is this a fuel issue or an ignition issue? Can you give me some help?

Rough Start part Deaux
 

Thought I might add more to my original post. Really hoping someone out there can help.
I checked the heat riser today and it moves freely. After warming up the car the butterfly still did not open. I also noticed the manifold was a little wet with fuel on the passenger side. Separately I put a volt meter on the coil. With ignition on it reads 6.5. Running it reads 10.5. Hot it dropped to 4.5. Going to check again after the game to be certain. Seems like a combo problem between the heat riser and the coil resistor wire? Some ideas would be appreciated.

The coil voltage should read approximately battery voltage when the key is in the Start position. When it's in the Run position, it should drop to about 8 or 9 volts due to the resistor wire in the circuit then. When you say the butterfly is not opening, are you referring to the heat riser?

As to the rough running upon initial start up, it sounds like you have a fuel leakage problem from the carburetor. One thing to check would be the plugs at the bottom of the secondary wells that have a reputation for leaking. These are pressed in steel plugs. You can fix that by either epoxying them in or there is an aftermarket kit with replacement machined aluminum plugs with O-ring seals.

Hopefully you are using pure gas with no ethanol.

Really appreciate the response. Yes the butterfly refers to the heat riser. Given the wetness in the manifold I will definitely check the plugs. No ethanol in the tank. The voltage as you outlined makes sense. I will double check. I also read that I should clean the ground wire between the block and the motor mount. It’s amazing to me how well the car runs once started. Starting issue is frustrating and will keep digging into it. Thanks again for responding. I am no mechanic but really enjoy the puzzle.

First I would wire the heat riser wide open. I did that on mine and used it as a daily driver year-round and never experienced any problems. Secondly since it seems to run fine after about a minute, I suspect as I originally said fuel leakage. It is probably still leaking after startup but not enough to affect the running of the engine.

Ok. Heat riser wired open. Also cleaned the contacts on wires to coil. Voltage is good. Car started right up. Warmed her up and she restarted fine. Let her set for an hour and restarted with quarter pedal. Started to feel like we solved it. Went to fill the tank and run into the store. 15 minutes later and she did not want to start. Misses like crazy. Shut her down and put the pedal to the floor. She roared to life. Could this be tied to the plug issue on the carb? Trying to figure out next step.

If it took a wide open throttle to start it, then it sounds like it was flooded out to me. IIRC, there's also pressed in plugs on the bottom of the primary wells. They are a little different and smaller than the secondary ones. You might try epoxying all four of them to see if that fixes the problem. Use something like J-B Weld.

Again Thanks. I will definitely take a look at this. Will let you know what I find. Really appreciate the ideas.