Suzuki 225 4 stroke

[meathauler]

My motor lately lost 400 RPM. It was running 5200 and and now only 4800. I had the filters changed last fall. It was running fine till about 6 weeks ago. Several times out the hole it would run 4000 and then I stopped the engine. I took off again and it did fine. It runs all day and never misses or skips. I had a spare prop that needed work so I took it and had it re pitched from a 23 to a 21. Put that prop on and still never gained any RPM. I had a compression check on it last year and then again 3 months ago. Everything good on compression. I was told by a friend that it may be another filter that they didnt change. I was wondering what yall think.