Motorcycle Repair: Honda 90 1973, filter screens, hash marks

Question
I have 2 machines, 1973 and 1975 Honda 90's which exhibit the same problem. Don't let the age let you assume there is a wear problem because these machines have almost no mileage (300) maybe.  Both start easily and on occasion seem to run normally. No power at low rpm.  It is not an overheat type of loss but seemingly a fuel situation. They act as though they are flooded but there is no sigh of this in the exhaust.  Higher rpms help keep the machine running and keeping the machine in lower gears often allows almost normal operation.  Slowing down to climb a hill is worse.  The floats are perfect- adjusted to book specs. the carbs are clean enough to eat out of. Honda dealer had no luck! parts look like new filter screens are clean. Tank lines replaced. No debris in tanks and new line filter just in case. carb has fuel. Adjusting the choke and or tank/reserve lever does nothing. Any suggestions would be much appreciated.

Answer
This is a puzzle.  It doesn't sound like a carburation problem but it still could be.  It sounds like a compression or timing problem.  I'd recommend running a compression test.  It should be 150 psi or higher.  Be sure to hold the throttle wide open when you check the compression so you're not throttling the intake.  Also check the spark timing.  Make sure it's advancing correctly.  At idle the coil should fire at the "F" make on the flywheel and when you rev up the engine it should advance to the two hash marks on flywheel.  

To rule out the fuel, try adding a little choke when you climb the hill and see if runs a little better.  If that doesn't help, try turning the fuel off and make sure it doesn't make it run better.  If either of those help, it still a fueling problem.

Please let me know what you find.

Regards
Rich