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Message Subject: 25 Mercury 2 stroke Vs. 2008 20 HP Yamaha 4 stroke

cast4musky

Posted 7/11/2011 10:26 PM (#506704)
Subject: 25 Mercury 2 stroke Vs. 2008 20 HP Yamaha 4 stroke

Posts: 865

I had a day off today so I wanted to experiment while I was fishing, So I removed my 25HP Mercury 2 stroke tiller electric start motor that was on my boat. And I Put on a 2008 20HP 4 Stroke Yamaha electric start motor. There was a big difference in these two motors, the 25 2 stroke ran out at 25 mph, while the 20 4 stroke only went 14 mph. I was quite disappointed to say the least, I new the 25 was more powerful but the Yamaha was just a dog. compared to the Mercury 2 stroke. It was nice to run straight gas, o oil mixing and it was so quite but No Power... I tried all the tilt positions but that did not help....... Are all the smaller 4 strokes like this ? I'm going to put he 4 stroke back on again ASAP 4 strokes S_ _ K Mike Sr.

esoxfly

Posted 7/12/2011 12:45 AM (#506712 - in reply to #506704)
Subject: Re: 25 Mercury 2 stroke Vs. 2008 20 HP Yamaha 4 stroke

Posts: 1663

Location: Kodiak, AK

Was the Yamaha propped properly? If you're not reaching proper RPMs it'll give you a "dog." Another question that comes to my mind is, "where has the Yammie been before you put it on?" I mean, was it laying in the garage for the last few years? Had it been put away properly? Are the shafts the same length?

VMS

Posted 7/12/2011 6:44 PM (#506865 - in reply to #506704)
Subject: Re: 25 Mercury 2 stroke Vs. 2008 20 HP Yamaha 4 stroke

Posts: 3508

Location: Elk River, Minnesota

Hiya,

Couple of things come to mind.. Given shaft length is correct, I would not be surprised at that much of a change. Going down 5 hp is a 20% reduction in power, along with going to a motor that is what I would assume to be another 60 pounds heavier than your two stroke.. If the motor is not propped correctly as esoxfly stated, and is over or under pitched, that will only exascerbate the problem...

Lots of variables here...

Steve

cast4musky

Posted 7/12/2011 10:26 PM (#506908 - in reply to #506704)
Subject: Re: 25 Mercury 2 stroke Vs. 2008 20 HP Yamaha 4 stroke

Posts: 865

Thanks Guys, I have thought this over very carefully and have removed the 20 hp. 4 stroke and put the 25 hp 2 stroke back on my boat this morning, I guess the noise, fumes, and the purchasing of, and mixing of oil every week is well worth the power that I have gotten use to. Thanks Mike Sr.

ToddM

Posted 7/13/2011 8:26 AM (#506933 - in reply to #506704)
Subject: Re: 25 Mercury 2 stroke Vs. 2008 20 HP Yamaha 4 stroke

Posts: 20258

Location: oswego, il

Like was said above 5hp is a huge difference. I have a 25 on my small boat. With just me my depth finder says 29mph. 4 people and the hull won't come up and the depth finder reads 13mph.

vegas492

Posted 7/13/2011 10:04 AM (#506943 - in reply to #506704)
Subject: RE: 25 Mercury 2 stroke Vs. 2008 20 HP Yamaha 4 stroke

Posts: 1040

Comparing a 25 to a 20 and you are surprised at the lost power? That is a big difference in power between the engines.

Speaking as a Mercury owner, I would gladly throw my 150 Optimax (2 stroke) into the lake for a 150 Yamaha 4-stroke. Yamaha's are a much better engine overall.

If I were you, I'd sell both motors and try to get a new 25-30 HP Yamaha 4-stroke with the money.

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