Reply To: Power – GT125
Let us know the results of the compression test results (after the engine is hot, and crank bike full throttle with both plugs out) but tell the mechanic also cause sometimes they leave one plug inside causing bike to fire, the spark plugs must be physically out of the engine not just disconnected from the HT casps.
Just adding to what Tom said above ^ , go with what he says , even clearances pay dividents (valves too loose or too tight gets worse when bike is hot) thus , alas , the speed woes happen as valve head isn’t being 100% efficient.
If we can deal with the engine from top to bottom , before we can focus on any parts outside of the engine (whatever is under the frame responsible for keeping the bike going)
Clutch may be next , have macro meters and vernier calipers ready to measure the clutch , HP losses can happen on heat fatigued old springs and worn glazed up clutch plates , hence Korea says in their service books clutch should either be “looked at” or “changed” around every 4/5k due nature of the heavy bike with 2 hungry pistons , it can tax the clutch a bit.
keep us posted!