Starts, idles, then rough for a bit

[Nate S]

1964 Sport Fury, 426-S mostly stock. Holley 3310, no choke, stock mech fuel pump. From cold I can start up and it will idle right away. I can then put it in gear and back up or whatever. After about 20 seconds it starts running quite rough, often stalls, then recovers and runs normally from then on.

Seems like it’s burning the gas in the bowls and not getting a replacement soon enough. Mixture is ok, light tan plugs, 14 mpg. Any thoughts? Needles sticking?

 

[Demonic]

Is the heat crossover in the intake blocked? Sounds like a cold intake or fuel dropping out of mixture.

 

[Nate S]

Is the heat crossover in the intake blocked? Sounds like a cold intake or fuel dropping out of mixture.

I thought about it but left them open. No valve in the manifold anymore but the intake does warm up.

 

[toolmanmike]

No choke. You need full choke for a cold start and partial choke for the first few min of warm up. With no choke you are going to have to live with it.

 

[Nate S]

No choke. You need full choke for a cold start and partial choke for the first few min of warm up. With no choke you are going to have to live with it.

Interesting. I've used chokes before too but normally the engines needed them for initial running, here it's great for 20 seconds. If I hold the throttle a little further open it does the same thing. I have a cable around, I'll give it a try.

 

[toolmanmike]

Interesting. I've used chokes before too but normally the engines needed them for initial running, here it's great for 20 seconds. If I hold the throttle a little further open it does the same thing. I have a cable around, I'll give it a try.

If you have a choke but it's not hooked up you can simply close it when the engine acts up. Yes you may have a fuel issue. The accelerator pump wells on Holley's have their own reservoir and if fuel evaporates out of the float bowls all of it is probably not gone. You might want to crank the engine for 5-10 seconds or so cold to fill the carb before stepping on the pedal to give it i accelerator pump shot. I would try the choke first then look at the fuel supply. You can install a small electric pump near the tank and hook it up with a momentary keyed switch to prime the carb. Once it's running the mechanical pump takes over.