how do I free up valves?

My bike was idle for 13 years. After cleaning up the carbs and
replacing the points, it starts easily now. I am getting some noises
that sound maybe like a mild backfiring and I wonder whether the valves
are sluggish in closing due to gummed up valve guides and stems. But
maybe backfiring would indicate a timing problem? I am kind of ignorant ...

The engine is a two-cylinder inline with single overhead cam ('76
CJ360T). It has a two-inch plug or cap covering each valve spring. I
squirted Marvel Mystery Oil on and around the valve springs, but I don't
have enough experience to know whether that is sufficient.

Should I try to spray aerosol Liquid Wrench between the coils of the
valve springs and onto the valve stems? I'm wondering whether it will
help and whether it will tend to make the crankcase explode ...

 

Backfiring out the exhaust and backfiring out the carbs can be caused
by lean mixture or valves that don't seat correctly. If the valves
don't seat, the fuel/air mixture is too lean and you'll hear the
piffle-piffle-popping sound out the exhaust pipe...

One rider told me that the light valve springs on his Suzuki GS-750
were so weak that whatever inlet valve was left open when the engine
was shut off wouldn't seat properly for the first few turns of the
engine and that he'd hear that cylinder spitting back through the
carb...

Oil leaking past the intake valve guide oil seals will get hot and
carburize onto the intake valves, keeping them from seating. If allowed
to continue, unbelievable balls of oily carbon will reduce air flow
past the valves and stop them from seating and they will burn.
Chevron's Techron gasoline additive is supposed to clean the valve
heads off, and if you do have such deposits you might try a shock
treatment of Techron Concentrate in your gasoline...

Probably wouldn't hurt anything at all...

Old time mechanics used to drip a light grade oil, like your Marvel
Mystery Oil, 10 weight gas turbine oil, or even automatic transmission
fluid into the carburetor while the engine was running at a very fast
idle. It would produce smoke in great clouds, but the engine idle would
be faster and smoother when the valves were lubricated...

 

"Ed's Red is equal parts of acetone, odorless mineral spirits, kerosene
and automatic transmission fluid", according to one gun NG. Gotta keep
that acetone away from any wooden or plastic parts...

 

Marvel Mystery Oil is red, so maybe it has something in common with ATF.