This engine has a small replaceable screen type fuel filter unit. I replaced the cartridge and now engine runs a little rough and hesitates at trolling speeds which it didn't do before. Tohatsu parts are almost impossible to get except at distributor. Am considering just replacing entire filter unit with a universal straight inline. Should there be any problems if I do this? I also have water separator unit which I change yearly.

Check your plugs. I have a 2 stroke, but when mine hesitates, especially at idle it has always been the plugs. Doesn't happen a lot and they have barely an carbon on them. Since the plugs on mine are so expensive I just clean them with a wire brush and the problem goes away.

We can help you with Tohatsu parts.

Personally, and unless your motor is under warranty, I would do away with the filter, go to a straight line and a 10 micron Racor water seperator and that should be all you need.