Hi kingfishercam
Its Funny you talk about that. Ive just fitted a 1961 40 evinrude i got off blah blah poop and it started first go but it kept backfiring a bit. i talked to a at home mechanic he said how to fix it. and i asked him about fuel water seperator he said my motor is to small and unnessassary. As it didnt work what he said And im still learning about boat motors, but i know cars. I fitted 2 new points and condensors and cleaned out the carby which was in excellent condition and fitted a seperator anyway.I went to a Ray at fine tune marine Prestons as he was the only person that would touch an old motor,He got it going in no time and tuned it well. He said that is a great idea to fit the seperator and change the filter when i service the motor which will be the same time i change my wheel bearings.
The guy at BCF where i bought it said that water builds up in the fuel tank as it is storage. my concern was if the pump could handle it and just last week i got it on the water i ran it first straight from the fuel tank cause i knew it would work, as i tuned it at high speed, then i connected the seperator i ran it for 45 mins at full speed not only am i happy as larry that my motor is cool but the seperator worked well and did not miss a beat.
i had a 35 Johnson previous the head gasket blew after lots of work in a year and a half.
if it was me with your 25 i would fit it knowing what i have learnt till now.
Kind Regards
Stuball