I purchased the above engine this winter in Texas. It may have sat for over a year. It had a half tank of fuel so I filled it up (30 gals total). The engine ran good until it got down to half a tank then it idled rough and at full throttle ran at about half speed. I changed the fuel filter and put in 8oz of ethenol stabalizer. It ran good for a half hour trip. We sat for about an hour and when we headed back it again idled rough and at full throttle ran at about half speed.
What does your wisdom suggest for a solution to this problem.