My truck (1968 F-100 302 c4) won't run unless the choke is almost completely closed. Even when the truck is good and warm, it will not stay running unless I manually move the choke flap to an almost shut position. If I do this, the truck will idle decently well. If I try to drive, it shuts off, because pushing the accelerator causes the flap to open slightly and allow more air to pass into the intake.

This led me to believe that I have a vacuum leak somewhere that is allowing enough air to pass into the intake (by some route other than the proper one) to prevent a super rich condition. But, I checked all the vacuum lines to make sure they were attached and not broken. I also sprayed carb cleaner all around the carb while the truck was running to see if there were any faulty gaskets. It doesn't seem like I have a vacuum leak.

I'm thinking now that I might not be getting enough fuel into the intake to mix with any more than a tiny bit of air. In other words, a little bit of air mixing with a little bit of gas, and the truck runs. More air mixing with still just a little bit of gas, and the truck dies.

Sound like a decent theory...?

If it isn't a clogged fuel filter, what could it be? I have a new fuel pump and the fuel tank isn't rusty.

Thank You.

 

How are the IDLE mixture screws on carb?? Might be too far in? cutting off the needed fuel, thus only after closing choke does it cut enough air off to get fuel mixture rich enough to run??

 

It probably have a bad vacuum leak. check the base of carburator and vacuum lines, pcv valve for leaks. check intake gasket also.

 

intake yeah, i agree

 

Do you mean the intake gasket where the intake meets the block? Is there any better way to check other than spray carb cleaner?

 

Hey 68 Short bed, if it has power brakes check the booster.

 

Nope, it doesnt have power brakes...

On perhaps a similar note...on the passenger's side of the carb (Autolite 2100 2V), down low, between the choke housing and the body of the carb, there is an adjustment screw, and what looks like a small cam with three different settings. I'm guessing it is used as an initial choke/idle setting for when the truck is first started. Any idea how to adjust or set this?

 

That screw is a choke adjusting screw. If you look at how that linkage works, it opens and closes the butterfly plates in unison with the chope plate. I think that screw is used to set the cold idle. I can't remember off the top of my head for sure. But I think you screw it in or out to get that cam to rest on the screw depending on how you need your choke set.

Get under the hood and hold the choke flap closed with your left hand and work the throttle with your right hand. If the truck runs good then you definitely have a very bad vacuum leak.

 

Finally found the vacuum leak. The gasket between the carb spacer and the intake was completely shot. Only cost me $16 for an entire carb rebuild kit to replace it...

Now I am just fine tuning the carb.

Another problem: Truck will run fine at idle when cold, it also runs just fine when warm and moving. Once it is warm, and I come to a complete stop, it will die...?

Suggestions?

 

If you put the entire kit in make sure your float level is right. Start out with running the air/mix screws all the way in then back them out about 2 turns. Make sure you don't have the base idle set too low or too high when adjusting the mix screws. That should get you in the ballpark. I usually run the screws out 1/4 turn at a time till the idle smooths out. Hope this helps. Rob

 

Any suggestions on setting the float? What sort of problems will an incorrectly set float cause? How will I know when I have it set correctly?

 

One of the obvious problems will be fuel running out of the carb. It can also act like it is running out of fuel. follow the instructions that came with the package to set the float level. You should also check where the chock is at now when the engine is hot and idleing. It may be malfunctioning and closing when you let off the throttle. I had to disconnect the choak and install a manual one to fix it.