Treating gas, follow up

Folks,
I meant to follow up on an issue I had posted last year about my Yami SX motor and a problem I had while getting ready to store for the winter.
At the end of last season as I always do, I use up most of the gas in the tank, add Stabil, go for a ride to run the stuff through the motor and then do my storage tasks. Last fall, after treating and running, on the way back to the dock and at the dock, my motor started surging, revving up and down. When throttle was applied, it seemed to run OK in neutral but idling was very rough.
Since I was ready to haul and prep for storage, I wasn't able to investigate the problem and had to wait until this spring. In the meantime, I posted a message on this board asking if anyone had similar issues after adding Stabil. All the replies were negative and said that adding a larger concentration shouldn't make the motor surge.
Now to be honest. I usually add about an ounce of stabil per gallon of gas for winter storage and I try to store my boat with 20 gas or so of gas. Last fall I may have had a bit less gas that previous years and in a senior moment, added a full 32 ounce bottle of stabil.
So this past spring I was nervous about what I might experience when I go the boat running for the season. Lo and behold, there were no issues and the motor ran perfectly all season.
I can only suspect that the higher concentration of Stabil somehow confused the O2 sensor which then varies the air/fuel mixture.

The funny thing is that the motor didn't surge when started in the spring with last years gas. I didn't add new gas until I took a test run (with my fingers crossed).

I think this year I will be more careful when I add the Stabil.
Regards,
Seasick

Doc Stressor said:

There is really nothing in Stabil that can cause an engine to run rough except for the high dose of detergent that it contains. The marine versions contain a lot of detergents that can dislodge deposits that form on the inner surface of the tank and other parts of the fuel system that contain air such as the top of the VST. The result can be similar to what happens when ethanol containing fuel is first used in an engine that has only seen conventional gas. The varnish tends to flake off and clog up the fuel system.

My guess is that over the winter the varnish particles became fully dissolved so that your engine ran fine in the spring.

Click to expand...

Could be I suppose. I was just happy that whatever it was, it went away. That doesn't happen all that often.