Desperate for help...no one seems to be able to find and fix this problem. My 1983 pickup runs great on cold start, but after warming up (about 15 miles or so) begins to jerk and shudder - same feel as vaporlock. Have replaced coil, plugs, wired, cap/rotor, all helped but same problem. I had a 75 ford one time that would suck air around the throttle body when the engine heated up and the steel started flexing, causing the engine to behave similarly. Could there be a similar problem here? Don't believe it's electrical, as it seems to be worse on less than 1/2 tank of gas. The jerking/shudder is very violent, looses power, when I give it gas there is no response at all, then it'll pick back up. Best I can do is hold light pressure on gas, downshift to where it will stay moving, but eventually will not pull itself. I can shut if off and sit for 10-15 minutes and get another 10-15 miles out of it before it starts jerking again. I hope you guys have seen this before-I'm at a total loss! Thanks.

 

It's a dirty fuel filter. Seen it a thousand times.

 

no kidding...so the warm up and all that has nothing to do with it? I'm gonna get them changed asap...I sure hope your right.

 

When you fire it up, dirt and debris in the filter slowly starts to swirl around and get in line to plug it up. Alot of times, it will get so bad that it actually starves the engine and stalls. Then when you shut it off for a few minutes, the dirt settles back down because there is no flow. Hence, the ability to run for another short time until it clogs again. I always start with the cheapest parts that could relate directly with the problem (if you can't pinpoint the problem immediately).

 

Awesome...I'm gonna change the one on the frame and the inline at the carb tonight...hopefully I won't be back whining that it's still happening! Thanks!

 

How cold is it? Mine behaved similarly when the carb would ice up, adding a HAI solved it.

 

I'm in NE Texas, 70 today, 35 at night...don't think it's too cold, it does it in the summertime too...

 

ah, that eliminates icing. Fuel filter for the win

 

Had the same problem with my '83. Had to rebuild the carb and replace the fuel filter. Carry a spare fuel filter, their easy to replace.

 

THANKS !!!! Finally got the filters changed...it worked like a charm...I'll definitely keep a spare in the toolbox, and probably rekit the carb...Thanks for the input!