Chris,
IDK if this could be it but you may want to take a look at the valve clearances again. This is from a thread back in August from SavageEarl I think.

Good hunting

"The valves sit in the top of the head.  The rocker arms sit in the head cover.
You open that joint when you replace the plug cap.  You put it back together with sealant between the surfaces.  If the sealant thickness is not EXACTLY the same as was when you took it apart, the valve clearance will be off.
Hope that helps."

When I first took it apart I saw it was just black form-a-gasket.  I ordered full motor gasket set so I had stuff just in case I needed it.  Than my Clymer book arrives and I see there isn't a premade gasket.  So in my reassembly I used Copper form-a-gasket but maybe I cranked it down a little too tight introducing a smaller clearance.

Thanks for the tip and I will check this out.

Tapping in time with the valves can be an issue.
I'd re adjust the valves, might even adjust them a tad tight just to see.

oil flow is very important the journals.  If you've applied to much sealant and blocked the oil path, you can damage the top end severely.

You might take off a inspection cover long enough to verify oil is flying everywhere.  There's a little pool the cams sit in that should be full of oil.

You should probably inspect it.
that bolt only goes thru a half round in the decomp shaft.
so if it's worn, you might need to replace it.

And I'm wondering, do you have it over tightened?
the decomp should only hit the rocker when activated.

in that area, only splash lubed, drain is next to valve.

You don't want any thicker "Form a Gasket' or sealant.  The head cover is also the upper half of the bearings for the cam - so if you raise the head cover up you will be getting too big of a clearance in the cam bearings......and this will be noisey and it will not properly control the oil flow.

The sealant you put on the head cover should only be about as thick as a pencil lead and be located in the center of the sealing surface.  You don't want the stuff to ooze out of the edges in thick globs as you put the head cover on - as that ooze can block the oil passages if put on too thick.  When you tighten the head cover you should just get a tiny bit sqeezing out of the mating surface.  Look at any stock bike and see that there is not a big glob of sealant......just a trace.  The sealant between the mating surfaces makes a good seal and there is no reason to have bunches of it oozing out.

I prefer to use the Yambond or Suzukibond.  It is black, made to seal these surfaces properly, it does not tack up real fast and gives you time to assemble the pieces.  I squeeze it from the tube into a little syringe and it is much easier to put on accurately.  

take it out and see if it goes away.