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So, I took my dads boat out about 2 weeks ago, and it started fine, and ran fine, but after about a mile or 2 on plane, the motor lost power. It didn't die completely, but if I tried to give it gas, it just bogged out. I could cut it off for a minute and it would get back up on plane, then cut out again. This went on through out the day. I got home and checked the water separator which I thought was the issue as it was maybe 3 to 1 water. Of course it wasn't as I took the boat out yesterday and it did the same. Just thought I'd get some hints on what to check before bringing it to the shop. Some other things we did try was putting in reverse which seems to run normal. Also not sure if was just me but it smelled as if were running rich (smelled heavy gas). I guess the other helpful information will be that its a 70hp Yamaha 2 stroke. Thanks in advance for any tips on what to check.

Those 2 stroke motors have one of two problems - spark or fuel. Take a 6 gallon tank with some fresh fuel in it and hook it directly to the motor. Bypass everything else - fuel line, water separator, etc, If it runs fine with this set up, you have a fuel problem, if not, you probably have a spark problem.

Same motor, near identical problem couple years back. LOng story short, Took out fuel filter ( which DID NOT look dirty) cleaned with carb cleaner, Ran like a it was new again. heck a new filter bout same cost as can of carb cleaner. Anyway worth fifteen minutes to check. Thats my .02. Love that motor!!

I had a similar problem on my boat. Turned put to be a broken o-ring on the fuel filter. If I ran it in the driveway or at low rpm, it was fine. It just cut out once I was at high rpm for a while. I figured that at low rpm the bowl on the carb could stay full. Once I opened it up, it was sucking gas from the bowl faster than it could get it from the fuel filter, and it would run out after a short while. I figured this out after tearing the carb apart to find nothing wrong. Replaced the o-ring and it runs great now.

my problem like that was fuel pump

Had that symptom with a 115 hp 2 stroke yammy.
The 115 had a oil reservoir under the cowling and the float was bad and not oiling right.
Filled the reservoir manually with oil and was OK until a new float was installed.
Another time, same symptom, that was oil related also.
The little motor on the oil pump tank went bad.
Again filled oiler on motor until the pump motor was replaced.
Not enough oil could possibly account for your gas smell.
These motors go into "limp mode" when it detects a problem and only runs about 2000 rpm.

I had the same problem on a 2004 2 stroke 150 and the filter on the external oil tank was clogged. I cleaned it with brake cleaner and it's been running great.


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Had a similar issue about a year ago. Mine turned out to be clogged carb jets. A good cleaning fixed it right up. However, your issue stating that it gets on plane and then loses power sounds like it could be related to the oil pump or a stuck reservoir float sending it into limp mode. I've had that be the issue before, too. I am no mechanic by any means, just sharing my experience. Hope you get it worked out. April is a devastating time for the boat to act up.

Also check for a leaking fuel line or collapsed gas primer bulb.

Are you saying you pulled water separator filter off and it had 3 parts fuel to 1
Part water? As in 25% water? If so I would highly recommend draining fuel tank as much as possible and refilling with good gas. I would also check your fuel lines for internal degradation.

thanks everyone for all the replies!

@leonreno - more like 60-75% water.

@JT - the primer bulb stayed full. Leaking line would cause bulb to collapse correct? I also think what you said about the oil hits it on the head. But only time will tell.

I will update evreyone when i try these things .