I know these motors well. Well enough that I can tell you that the Tillotson's do NOT like gasohol. The o-ring on the main jet is not compatible and neither is the tip of the float needle. YOu can get a Viton o-ring for the jet if you don't destroy it while removing same. The float needle can be replaced with that from a chainsaw, can't remember which (the internet is your friend). Lastly, the plastic fuel bowls tend to warp and the cork gasket for same becomes hard a rock from the gasohol. It is time for you to move on from the Tillotson, in my opinion.

What I did to keep my motor alive is to get a WMC 25hp carburetor. It is not a completely bolt-in operation but it can be done. Think I had to change the reeds because the holes in same don't exactly line up with the WMC carb. Also, you will have to grind away some metal on the forward cowl cover "hook" near the fuel inlet. If you go down this route, you want an earlier WMC carb, something like a WMC-19 if memory serves me correctly. Timing (at idle) is a little different as well.

I can definitely tell you that after I did this, I felt more confident in the motor and it runs like new. The boat flies with the max pitch propeller made for this motor. If you upgrade to a 25hp carb from an 18hp one, your fuel economy will be the inverse of your horsepower gain, but for me was desirable and well worth it. It pushes a 1967 Duranautic 14, "Abalone."

Regardless, good luck to you and let the community know what your plans are for your motor.