Mis-adjusted valves = bad idle?

I recently bought a '79 CX500 with very low miles. The previous owner said
it was having idling problems on one cylinder (right side), so I anticipated
a carb rebuild. It also seemed to me that the valves were quite noisy on
the right side, but he explained it away as being pushrod noise. Hmmmmm.
Must not have been any pushrods on the left side.
Anyway, the idle problem turned out to be that the right cylinder was simply
not firing at idle. There was a good spark, but the non-firing could not be
resolved with the idle air screw; it had no effect on idle. Also, once the
throttle opened to, say, 1/8 throttle, or if you put the choke on, the
cylinder kicked in, and the bike runs like a charm up to full throttle.
SOunded very much like the slow jet was plugged, right? I ordered a carb
rebuild kit including new jets, and they finally arrived yesterday, so I
pulled the carbs, and there IS some crud in the right carb which I am
clearing out. While the bike was down, however, I checked/adjusted the
valves. Left cylinder's valve tappets were a little loose, but pretty close.
The RIGHT valve tappets appear to have been adjusted using the metric
readings as imperial readings. They were uniformly way wider than they
should be (took about four full turns of the adjusting bolt to get them near
the right settings) I'm guessing they were at least 4 to 5 times over-gapped
(new word).
I anticipate a much quieter engine when I'm all finished, but now I'm
wondering whether the valves could possibly have been the primary or
contributing cause of the bike's inability to idle? Any thoughts?

Thanks
\brent

 

With that much gap, the intake duration would certainly be short.

 

One thought: Does that engine use hydraulic valve lifters? If so,
you could be seeing sticking lifters on the right side, and adjusting
this lash out could mean serious trouble. Otherwise, look for wear
on the cam lobes or lifter surfaces. I doubt that someone would have
adjusted just the right (or left) side to leave them different.

I bet on the crud being the primary problem, since that cylinder did
fire under some conditions. You won't get good performance with too
much valve clearance, since the lift and duration are effectively
shortened. But extra valve clearance also imposes a great strain
on all of the valve train components, and could lead to catastrophic
failure.

 

You might want to pull the pushrods for the right cylinder to be sure their
not bent.