I recently replaced my fuel line and on a 200 optimax. I went to sail and ski it was the closest place that had it and I took a piece with me and the guys there said that it does not matter between 5/16 and 3/8 line. 3/8 is what I had on it and they sold me 5/16. I have run the boat sence then and it never missed a beat. Is this alright do I need to replace it with 3/8?

I replaced my lines on my 225 efi. The line from the tank to the bulb was 3/8" and line from bulb to motor was 5/16". My mechanic had only 5/16", but I wouldn't hear of it. Wanted to go back as original, and did so. I guess it's just preference, but I'm pretty anal when it comes to my boat. Probably not going to make a difference for you with the 5/16" all the way, especially if it is running great without any problems.

I would use the 3/8 fuel line. You need to maintain volumn. It would also require the mechanical fuel pump to produce less vaccuum to deliever the high volumn. After the engine gets older, the mechanical pump will not vaccuum as much, so a larger fuel line would still require less assistance to provide the fuel.