Hi everyone,

Please, please, please help me on this one!

HS81 once warm bogs down under full throttle.

Sounds like a blocked exhaust/ stuck blades. But only does it after about 10-20 minutes of use.
Tick over is unaffected.

Will be fine again once cool.

So far it has had a new fuel pipe from filter to carb as the old one had a split.
A new tank breather. New spark plug.
Pressure tested and found a leak from the crankcase so that has been resealed.
A needle bearing had failed on the lower gearcase.

When apart I blew through the exhaust and it seemed clear, piston and cylinder looked in good nick.

Any thought and suggestions muchly appreciated.