I have acquired a DT85 and it runs great for the first 15 minutes then it boggs down and won’t do anything other then slightly above idle no matter where the throttle is placed. I replaced the fuel filter, new gas tank, new spark plugs, seafoamed it. I have had it out four times since I got it. It hadn’t run in 4 years. The first time I had it out after getting it running it ran great for two hours. It was the next three times out that this bogging issue has come out. I don’t know anything about boats so if you think you can help me that would be great.