I had that on a Midget just after a head change. I'd oiled the guides and
stems before assembly, and checked oil supply from the rockers. Proved it to
one cylinder, but all leads were flashing with a timing light as they should.
Swapped leads and plugs around but it stayed with the cylinder. I even
clipped the timing light onto other plug leads and pointing it at the rockers
could 'freeze' them. By using the variable control I could freeze them in any
position between fully up and fully down, and could see no difference on the
rockers for the affected cylinder and any other, which would appear to rule
out a sticking valve. It only started happening when hot, but after a couple
of hours of investigation stopped, and didn't do it again.
----- Original Message -----
That happened to me, too, when I first had the head rebuilt with new
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