I'll usually put redex in mine at a very high concentration (whole bottle to half a tank)
Straight after I bring it out of winter storage.
It usually runs lumpy after being sat for a while as I don't drain the carbs, so I guess there'll be deposits from evaporated fuel in the carbs. After a good run it then runs like new.
The only thing I did find when I recently rebuilt my engine was a purple/red oxidation over the piston, valve heads and plugs. I assumed it was just running hot, but recently looked at a spark plug diagnosis diagram that suggested red deposits were the result of fuel additives.
No harm done, just an observation.
