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OX66 frustrating issue

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  • OX66 frustrating issue

    Hello all, I've been having a very frustrating time with my Yamaha 2002 OX66 250 HP 2 stroke. All last summer it was running just fine except that towards the end of summer I notice that if I was running open throttle it would start slowly dropping RPM's on its own. If I came off of plane and shut it down for a few minutes, once I started back up it would run normal for the rest of the day. So a few months back I decided to do all of the maintenance and try to fix this issue, so I went to the dealership and they advised me that I should use Ringfree to clean the combustion chamber (which has never been done before). So since I added it (small bottle to about 75 gallons of Ethynol gas) my problem got worse, much worse. Now my plugs appear to get fouled up and the last two times I've taken her out I've barely been able to get up on plane. I've replaced the spark plugs about 5 times and no real fix. I can start the engine and she'll fire up however now it idles at like 400-500 rpms for the first couple of minutes then all of a sudden wakes up and idles between 700-800 or so. I notice that at times the engine shoots out exhaust (not really smokey) and then the engine shakes (rough idle). At times its even made a loud backfire sound then either shut off or idled slightly better. I'm assuming that maybe the ringfree broke some gunk loose and that's the engine shooting it out. However I'm being told that it should cause all of the failure i'm experiencing. Also if I start to accelerate it in neutral (not under load) it'll surge from 1000 to 2200 rpm's or so and eventually shut off.

    Here's what I've done so far:
    Had injectors cleaner (at a professional shop), replaced VST filter, replaced the 3 low pressure fuel pumps, replaced engine fuel filter (including the cup, spring and O-rings), cleaned O2 sensor and holder (contained lots of carbon buildup), replaced fuel/water separator filter and cup, replaced primer bulb with Yamaha bulb, and had a professional flush and condition my tank. Now the engine is only running Ethynol free gas.

    I'd appreciate whatever advice anyone can give, cause I really don't know what else I can do. Thanks in advance