hi peter i hope the below helps you

following is quoted from the aircooled haynes manual
"Check and adjust if necessary the clearence of the appropriate valve according to the table below
Valve fully open --------------------
check and adjustNo 4 --------------------------------- No1 (EX)
No 3 ----------------------------------- ------- No2 (IN)
No 2 -------------------------------------------- No3 (IN)
No 1 --------------------------------------------- No4 (EX)
(open/close the vales by turning the crank shaft)
The clearence is measured between the end of the vale stem and the rocker arm, using a feeler guage of the appropriarte thickness.
The correct clearences are given in the specifications. Note that the clearences differ between exhaust and inlet valves.
Where adjustment is required slacken the rocker arm adjuster screw lock nut and turn the adjuster screw untill the feeler blade is a stiff sliding fit.
Re tighten the lock nut without disturbing the adjustment
Rotate crankshaft and repeat the opperations on the remaining valves.
regards
Chris