Giftman23

69 Cutlass 350 2bbl rochester. From a cold start, 1 pump of the pedal and it fires right up with no issues. However, after running and getting warm, it's a hard starter..continuously cranking until it catches, then sputtering for a few moments. If you shut it off after running, and immediately restart, it fires right up easily. Not sure if this is a fuel mixture issue, a choke adjustement or what. While running, the car runs well and does not show any evidence of carb problems. Adjustment advice required - Thanks!

oldcutlass

I'd do a quick recheck on my tune! Timing/ dwell, a/f mixture, spark plug gaps, and ensure my choke is operating correctly! I would also make sure my vacuum lines, fuel lines, and fuel filter are serviceable and connected!

MDchanic

At a time when it's hot, and you would expect it not to start, pour an ounce of gas down the carburetor and try to start it.

If it fires right up, then your problem has to do with fuel supply, either fuel leaking or siphoning out of the float bowl, or vapor lock. edit: or, as RocketRaider points out, evaporating out the vent.

If it acts the same, or is even harder to start, then you've got a flooding problem, possibly a heavy float or some kind of leakage from the float bowl into the intake.

I think an ignition or timing problem is less likely here.

- Eric

rocketraider

High-volatile fuel. It's becoming a common problem on carbureted engines with "modern" gasoline formulations.

What happens is when you shut it off hot and it sits a while, the fuel vaporizes out the carb vent and empties the fuel bowl. Then you have to refill the carb to get enough fuel to fire the engine.

A fact of life when you drive dinosaurs in a modern fuel-injected age.

You might want to make sure the choke flap is in fact completely open when the engine is hot.

oldcutlass

He states that it fires right up cold, so its not a vaporizing, or losing fuel problem! It could be vapor lock, but I put my money on the choke and/or tune!

Giftman23

Thanks guys...I do have another good carb (I believe) that I could swap out. Vaccum lines replaced, fresh plugs/wires, and checked timing...Was thinking it was some type of carb adjustment. I'll go over the idle and mixture screws, and try the gas down the throat next time I run it.

MDchanic

A fair point. He says:
That would seem to exclude fuel boiling or leaking out of the float bowl, and also vapor lock, as far as I can figure (vapor lock would keep the bowl from filling, and it's obviously got at least some fuel in it when he starts it cold).

As I said, the no-cost 1-minute test of removing the air cleaner lid, pouring an ounce of gas down the throat, putting it back on, and trying to start will clarify whether it is a lack of fuel issue, and put that detail to rest.

That leaves excessive fuel (like, say, boiling over into the intake, which momentarily floods it, but leaves enough fuel for that accel. pump squirt that is able to start it cold, after the excess fuel in the intake has evaporated) or ignition.

From the ignition side, he does say that he's changed the plugs and wires and checked the timing, and the fact that it runs well otherwise would seem to exclude the rotor, cap, and wires (which seem to cause the most problems under load).
That leaves points (dirty), condenser, and coil.
Heat soak is a real possibility as the cause of an intermittent in the coil or condenser. Swapping one of these at a time for a toolbox spare could do the trick.

I'm always interested to find the cause of these problems.

- Eric

Giftman23

Well, a deconstruction of the 2bbl carb showed some worn gaskets, most likely due to sitting for a long period. A carb rebuild kit was purchased and a friend helped me perform the rebuild - the car runs much smoother now, I have not had it on a long run to determine if the hard starts still exist but I imagine problem solved. Thanks for all the input!