I've been working on my neighbors truck. A 1985 1/2 ton with a 360. I gave it a complete tune up, but it would spit out the carb, then spit through the exhaust. It was most noticeable under load and acceleration. On further investigation, I could hear a slight thumping coming from the engine. It was most noticeable from the RH side. I could hear and feel it mostly from the valve cover.

I removed the valve cover, but didn't notice anything wrong. Then I removed the rocker shaft. I didn't notice any bent pushrods nor cracked/bent arms. I placed a pushrod on top of the valve stems and noticed that one of the valves is about 1/16" higher then the others.

I'm thinking a bad valve seat may be the problem.

My neighbor told me all that started a few days ago.

Any other ideas?

 

Time to pull the head. Might be the valve or the seat, but most likely both.

 

I would do a compression test first. It may or may not save you a whole lot of work but any and all info is welcome. You may find out it isn't just one cylinder or one valve.

 

I was thinking this after while at work (scary)

I noticed while adjusting the carb that it was lean. Probably lean for some time. Either the adjacent intake valve is probably bad or one near it.

I need to have someone come over to take a look at it. It's easy enough to put back together. I'm not doing any engine work

 

I'll try that if I get off work early enough to catch some sunlight.