Motorcycle Repair: compression s-90, consumption power, bill silver

Question
is there any trick of the trade you know on how get get a good idea on weather you have low compression or not. i don't have a compression tester. i know the valves are set right and the timing is good and my bke runs good on the road it just seams to be slow taking off from the start like the compression is low. thanks john

Answer
John, the specification is measured in PSI and that requires a compression guage to measure accurately. You should see around 160-175 psi with the early versions.

Signs of low compression could be:
Oil smoke from the muffler and breather tubes
Hard starting.. having to push start it to get enough compression built up to run.
Valves that need constant adjusting due to wear of the parts. (clearances are .002" cold on both valves TDC)
Backfiring through the carb/air cleaner or exhaust.
Poor fuel consumption/power

Things that affect acceleration:
Low compression :>)
Sticking spark advancer mechanism
Contaminated carburetor passages/jets
Carb needle setting incorrect.
Tight drive chain
Low air pressure in the tires

The bike weighs about 175 lbs, plus your weight. The engines were rated at 8HP when new. A good S90 should run from 65 to 70mph with a 150 lb rider in a tucked in position.

Bill Silver