The correct timing for a Boyer is 31 degrees BTDC (on the timing plate in the primary chaincase) at 5,000 revs. It has been documented that these plates can be out by a few degrees, so if you have the time and inclination, possibly worth the effort to check this.
Timing is best not done with the bike on the centre stand as the machine will vibrate across the floor.
Neil,
If your Combat has high compression you might find a little less timing might help say 29 to 30 BTDC. You'll know if 31 is too much as it'll ring like a bell when pulling away.
Cash