My tomos revival ran fine then started losing power and droped in speed whay do I look for, plug is fine carb clean, air cleaner clean bike has 1200 senior miles

Hello
Well i always do the easier method to find out the problem.
hers a few things to do to determine whats wrong.
1st pull spark plug and do compression test, a blown head gasket will lose compression.
if the gasket is blown then the compression test will read a low psi and drop suddenly
2nd worn piston rings will lose compression, the compression test will read a very low psi below 100 psi and may leak right down depending on how worn the rings are.

that would make you lose power.
have it tested to see which it is.

either way, a lose of power in the motor is caused by lose of compression in the motor.
you can do the test your self, you can buy a compression tester pretty cheap, just make sure you don't cross thread the connectors.
have a good weekend
Big Al