I recently helped my uncle swap out his 400m to a 460 in his 79 F-150. The motor is a 72 block bored .030 with rebuilt stock 72 heads, and a RV cam. He's got an Edelbrock intake and a Holley 750 carb and stock mechanical fuel pump. The thing will start up with no problems, and idle fine, it almost seems to flood out if I tap the gas before starting! The problem I'm seeing is that, if the motor is still a little cold, it will hesitate and studder a bit once the throttle pedal is pushed. It does it even in park if I tap the gas. I can't tell if it's flooding out out for a second or running out of fuel during this hickup. There is a see-thru fuel filter on it and the level never changes during this time. Any thoughts on what to check? I've adjusted the floats and it has the stock jets that came on the carb. Is it worth it to pull the jets and do a change? If so what should I go to?

Not looking for the fuel economy, just want to get a good solid running motor that will scoot when the gas is mashed! I know someone will say go to a smaller carb, but I've seen numerous 750's running on 460's and not have the same problems. I just need to figure how to tune it right.

 

Don't go smaller than a 750 on a 460. I mean, I have a 600 Edelbrock on mine, but it will get swapped for a 750 some day.
I am not familiar with Holley at all, as I only run Edelbrock carbs. Are you near sea level, or are you up a couple thousand feet or more? Your jetting will make a difference if you are high up, since carbs are set at sea level.
If it were an Eddie, I would say you might need a stiffer spring on your metering rods for the stumble, but who knows with the Holley what it might be.

 

I'm over in Virginia, so not too much above sea level. These are the stock jets that came in the carb when we pulled it out of the box. I guess I need to do more research to see what the stock jets are before going one way or another.

 

Sound like your idle mixture is to lean. Adjust the idle mix screws a bit richer. A lean problem gets better as the engine heats up. A rich problem gets worse as the engine heats up.

 

You might try adjusting the accelerator pump to kick a little quicker. You can turn down the screw or even change the plastic cam on the throttle shaft to open it a little quicker.

 

He mentioned that the problem changed depending on engine temp.

So I doubt it would be the accelerator pump but who knows. I would bet it is an overall lean idle condition.

 

I'll give it all a shot today!! Thanks

 

Adjust the choke properly and the problem will go away.

 

Sorry, I was away; Just bought a house and moved and stuff, just got back online yesterday.

Yeah, you might wanna check the choke if it is electric. I often adjust mine twice a year; Once for fall/winter and once for spring/summer. I bet the choke is open too much. Adjust it when it is cold and try a cold start. Just leave the butterfly open maybe 1/8 inch max and try it.

 

It's a manual choke. He got tired of dealing with the faulty electric ones, and swapped it out to the old style pull cable. I looked it over today, and adjusted the idle some it seems to work better, so I guess I need to keep playing with it.

 

Get that accel. pump to squirt a little quicker and you'll be good to go.