[TJ's GMC]

Hi there, checked out the album. Nice looking bus. Now onto the engine.

Been sitting for a long time. There's one possible issue. Doesn't matter if the motor has low miles or not....nothing hurts an engine more than sitting for ages. Gaskets dry up....top end dries....things start to rust. And with today's fuel the ethanol does a number in the tank, lines, and carb. Draining the fuel most of the time is not enough, you'll need to pull the tanks and give them a super good flushing. Then take a look inside checking for rust. Then you'll need to blow out the lines and replace the filters. Going through the carb would be a good idea and then fully tuning up the engine. Oil change first thing! Get that black tar out and put some nice high zinc rated oil in that thing. Then remove the valve covers and check/adjust the valves to correct specs. Then clean or replace the points and coil. New cap and rotor never hurt either. Also replace the plugs....now here is the opportune time to check compression! 125 PSI is the spec from a brand spanking new engine. If finding cylinders under 100 PSI I'd say your engine is worn out and burning oil which would be a part of the carbon issue, or you have valve sealing issues.

But as it seems the carbon build up is mainly on the intake ports and valve seats I'd say that the engine was either burning old fuel, or the a/f ratio is way to rich and the engine isn't burning All of it. Or there is excessive blow by through the pcv which would cause carbon build up as well.

Weak valves springs will allow a valve to stick. And a lot of gum and residue will cause that as well. Be careful as you may have some bent push rods.