I wouldn't even risk it. Pump the old gas out and start fresh. It could save you a lot of head aches.

Do not use it. Unless stored under pressure it loses octane very quickly.

I have a great article on this that I will try and find and post.

Just so we are all on the same page here, the motor that is in your boat does not require race gas right? I would be suprised if the race gas that's in there has deteriorated to the point that it's below 87 octane. If you had a high compression or boosted race gas motor, then I would not use it. But with your motor, I wouldn't be scared to run it mixed with fresh 93.

Anytme I have left race fuel in my race cars it evaporates,I guess being its vented.

Its make good parts cleaner

I agree. If you don't NEED the higher octane then you'll be fine.

I ve heard if you do not require the higher octane that it makes less HP.

I had a pump gas 93 blower motor that I dynoed at Dyno Tech in Memphis, They also make there own race gas. After all the tuning on pump gas , we made a few pulls on the race gas which was around 112oct, Its wasn't much diff in HP but it gained TQ, around 25.