Running rough

O.k. I have a small block chevy 350 in my Merc. Has run great for the last few years. The engine was a strong rebuilt when I installed it. I drive it maybe once a week. Lately it seems to run rough after a few miles of driving around town. Checked the plugs and the #8 was pretty clogged with gunk. Checked all the other and they were fine. Replaced the valve seals thinking that oil was getting past them. Seem to have cleared up the gunk/fouling problem.
The problem has started again. This time no fouled plugs. Checked all vacuum lines, torqued intake manifold, Replaced all plug wires. adjusted timing. Still runs rough after a few miles.
Any ideas, I'm stumped. Thanks all, -stick

 

Have you checked for a clogged fuel filter?

 

Just a guess of course, but if it's seldom driven and you don't use a stabilizer, I would suspect "stale" fuel. That could have also affected your plugs. The fuels we have now days is more inclined to a "short life" than in the old days.

 

Whats the vacuum? Gauge reading should tell you alot about what is going on. Even better get it on a 4 or 5 gas ****yzer.

 

All new filters and pump.

 

So how old is the fuel?

 

Just g***ed up. When I said "driving around town" I didn't mention said "town" is Los Angeles. You can go through a tankfull just getting across town. Haha