Hey guys, I have what I believe to be a continuing carb problem on my truck. Its a 76 F150 with the 300 I6 and the NP435 4spd trans. Upon startup everything is fine, but as I drive and the engine comes up to operating temp my problem begins. What is happening is as ,I leave from a complete stop and accelerate up through the gears, the truck stumbles terribly as I shift to the next gear and get back on the gas. If I accelerate slowly, almost feathering the gas, I still experience some hestitation but not this big stumble. I have had the carb rebuilt and the accelerator plunger and diaphragm replaced. I checked the choke and it seems to be working properly, although some mornings I don't get the real fast idle upon start up. What is strange though is this stumble doesn't always occur. Some days the truck runs and accelerates perfectly. Any ideas what I should look at next? Thanks for any help.

 

It might be the carb gasket. Had 1 go on my old Mustang. Ran like it was missing 3 out of 4 cylinders. Other then that, check to see if the carb mounting bolts are tight. If it's loose, wiggle it to see if there is a difference.

Just a thought, hope it helps
Walter

 

Hello. Check for vacuum leaks. I had a similar problem, it was the egr valve. I put a new one on and it did the same thing, act like the truck was running out of gas. So I unplugged the vacuum line to the egr valve and the engine runs smooth now.