The boat sits most of the time. I had problems starting it but when I got it started it would only go half speed.Got the old gas out and put new ethanol free 98 oct gas and Seafoam in it. Still half speed but occasionally would go faster for a short time. Later, I changed the spark plugs that had been in it for some time and it immediately ran full speed no problem. I ran it for a mile and stopped to fish for an hour. When I restarted it, it was going ok but then it was as if the gas had been cut off. I restarted and could only get it to half speed. So changing the old spark plugs (see below) had a huge effect but not for long. As it's a major hassle to get a friend to drive way out, put it on a trailer and drive into town and back, plus the cost of the local expensive dealer, I try to do what I can to do whatever possible if it's something a non mechanic like myself can do. Any ideas what might be the culprit? Thanks