Seafoam is a decarbing agent, and I don't think has the stabilizing agents (though I reserve the right to be wrong).
I'll relate the experience I had with my 99 225 optimax. It was a repo, probably sat for 6 months. It started fine on the muffs and all was well. We dragged it down to the lake for the test ride, and idled out of the no wake zone and floored her... she started to plane, studdered and died. I could get her started, but she'd soon die again. I suspected old gas and even asked the guy if we shouldn't go put some fresh gas in it before heading to the ramp, but nah...
We rowed back to shore, luckily, not far.. well, let me re-phrase... HE rowed back to shore.
We got back to the dealership and he rigged up a fuel pump to pump the gas out of the tank, put in some fresh fuel, and voila.
Based upon my experience, I'd strongly suggest you pump out what you can. However, knowing what *I* would do, I'd top the tank off with regular, maybe dump a little 108+ octane boost (to raise the octane of the original gas) and HOPE it worked. Oh, I should also mention that my motor's under warranty
. If you've ever seen Dorf on fishing, I'm Dorf on boats, so if you blow your motor because of what *I* would do, it only serves you right.
