Motorcycle Repair: have to hold down starter for while on 82 Nighthawk, rubber diaphragms, plug caps

Question
My '82 Honda CB650SC always had trouble starting in the cold, but more recently even in mild weather I have to hold down the starter for 5-10 seconds. The engine seems to catch, but will die immediately if I release the starter before it's built up to about 1500 RPM. This is with the choke wide open and the battery well-charged. The problem is much worse in the cold or if the bike hasn't been started in the last day or so.

Would appreciate any insight.

Answer
Joey,

It sounds like it's lacking fuel for
some reason. Check for a good
fuel flow from the tank.

-Sometimes the fuel petcock valves
get plugged or have faulty rubber diaphragms.

-Have the carbs been cleaned recently?
Gas tends to varnish and plug idle
and other carb jets quickly these days.
Check the floats and float needle valves.

-check for cracks around the carb mounting
rubbers where it might be sucking air in.

-It might be a good idea to have a
compression or leak down test done
to determine the engine condition.
It should have around 150-170 psi ideally.

-If it always starts hard, maybe you need
a size larger idle jet.

-try some new spark plugs and check the plug caps,
they should have about 5000 ohms resistance or less.
-if you are not, use 10w30 weight oil, it might turn over easier.