This has been kind of a cluster trying to get everything straightened out the last two weeks. The 400 in the truck I just bought ran and drove great until about two weeks ago I noticed gas leaking from the accelerator pump on the carb so I mopped it up and went for a test drive to see how much was leaking and how quickly, about a mile out of the driveway the engine started to hesitate or pop (you could feel it in the gas pedal as well as hear it) so I took it home and figured it was something with the carb. After it was rebuilt it was still happening but only when on a hill or when under a load, you could speed up but couldn't get on the gas much. I called a couple shops and they all recommended a local guy to bring it to who they figured would know since none of the shops knew what was going on. This brings me up to Saturday.


On Saturday I brought it to this local guy, he called me sunday and said after adjusting the carb and choke more it still wasn't going away and so he was going to check the plugs to see if they were fouled. He calls me today and says he replaced the plugs with new motorcrafts, new plug wires, and a new cap and rotor but it's still doing the same thing so I'm going to pick it up tomorrow and I'm out $300 for nothing (why I avoid shops unless I absolutely can't figure something out).


The guy who was working on the truck says he thinks it's a rounded over cam from the modern oil not having enough zinc in it. Another buddy of mine who also works on these trucks a lot thinks it's burnt valves. I'm leaning more towards the burnt valves since I've ran the newer oil in a these older engines for the last 5 years and have never had an issue with it.


My question is whether or not there is anything else that should be checked. Wednesday it's more than likely going to get a new engine unless I can get something sorted out.

 

assuming the carb rebuild is good and properly set, I would suspect the coil or problem with timing (including vacuum advance)...

 

A vacuum gauge is maybe under 20 bucks new, or borrow one and hook to a source of manifold vacuum. With this tool aka "poor man's Sun machine" you can determine the health of the entire engine to include valves. Worth investigating before condemning it.

 

Carb build should be good. The guy I brought it to said everything looked good on the build, timing was good, and that the ignition system was all good.

A vacuum gauges is next on my tool list, I'm starting to realize how valuable they are. A vacuum gauge was hooked up to it I guess so I'm not sure. I'll get the details of everything that was done to it over the last couple days tomorrow. I did talk with a relative who has worked as a ford mechanics for a long long time and he said the double check the power valve since they're notorious for failing so I'll be checking that tomorrow.


I'll post up what I find out tomorrow.