Motorcycle Repair: Honda CB 500, honda cb 500, point gap

Question
Hi Falcon-
I have a question about a 1973 Honda CB500. I bought it from a guy in May who had had it in his garage for a long time. it only has about 12,000 miles on it. I had the carbs cleaned and professionally rebuilt, the tank relined, valve clearance checked, and that was about all it seemed to need. (It's a beautiful bike.) I've put about 1000 miles on it since then. Just recently, I started having two problems at the same time. I'm not sure if they're related.

First, when I start the bike, I get a kind of knocking/slapping sound. (Not sure how to describe it, but it happens in quick rythm with the idle speed.) At first I thought maybe it just needs warm up time because it is getting colder. Once the bike is warmed up, though, the knocking goes away, but the rpms are slow to fall off when I let off the gas.

Any thoughts?
Thanks very much,
Dan

Answer
Hi Dan.
 Because it is an early-mid '70's bike, you do not have an electronic ignition, unless the previous owner retrofit one onto the bike.

 You have the old-fashioned, and easy to fix points.  It means adjusting the timing and the point gap as well as all of the other things along with regular replacement of the points.  Your repair manual will have all of the specs and proceedures for that.

 As far as the knocking sound, that sounds exactly like valve tap.  The valves may have been adjusted, but they may have been adjusted improperly (it must be done with the engine stone cold) or they may have missed locking one of the tappetts properly.  You may want to check the cam chain tension as well.

Good luck.
FALCON