Hi..
Someone offered me 5Gal. used Fuji50 gasoline engine.
He said that it runs excellent.
If I buy it,is it enough use 5gal more in the future without any changing parts?

I never used Fuji engine before.
Please give me some idea about 5gal used engine. Would you buy it?

Good to go. Stick in a plane and go fly it for the next 5-10 years. If it hasn't been crashed, has always run a reasonable oil ratio, has not been run lean or dry on oil, which can be somewhat checked by noting good compression, then if I was in the market for a Fuji and the price was right it would be a do-er.

Sorry about qualifying all that, but that's the way I woud make the decision.