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Old 05-23-2016, 10:03 AM   #1
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Four stroke single cylinder outboards

Just bought a used Yamaha 4 stroke, single cyl outboard and a used Avon 9' RIB with the idea that this package would be less weight, easier to haul and shorter on our stern davits for our canal trip this year. (Our usual dinghy is an 11' 4" Achilles with a 15hp Yamaha 2 stroke 2 cyl that we customarily tow).

Had the local Yamaha dealer service it and check it over before we launched and he said all was in good condition.

I thought that 4 strokes were supposed to be quieter and have less vibration than 2 strokes, but boy this little motor is loud and vibrates to beat the band.

Is this usual for these little motors?

David Hawkins
Deer Isle, Maine
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Old 05-23-2016, 10:53 AM   #2
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The single cylinder is the reason.

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Old 05-23-2016, 11:16 AM   #3
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Yes, those little single cylinder 4 stroke engines do vibrate a lot.

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Old 05-23-2016, 11:47 AM   #4
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Four stroke single fires every other turn, or every 720deg of crank rotation. Two stroke twin fires twice per rev, or every 180deg of rotation. Huge difference. Four little hits compared to one big one. Small four stroke OB's are one of my favorite things to gripe about. Infernal beasts...

I would not want a four stroke with less than three cyl. Threes can be quite social, but not to be for a little dink.
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Old 05-23-2016, 12:00 PM   #5
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Until this year I had a 5hp Honda (one cylinder) on our dink and hated it. Don't get me wrong, it always RAN, but it was loud, hard to pull and vibrated like crazy.

Bought a 9.8 2 cylinder and its like going from a Hugo to a Cadillac. Actually, it was probably better than that. Did I say I hated the Honda?

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Old 05-23-2016, 12:54 PM   #6
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For some reason unknown to me, the small Yamaha 4-strokes have often impressed me as being extra noisy. I can always tell when one goes across the bay as they are so loud. Yet the big Yamaha's are wonderfully quiet. I too hated our little Honda, it always ran, but never properly and it was always hard starting. The best was a Mercury badged Nissan, smooth and quiet, easy starting, I wore it out. Now we have a Tohatsu 6hp, not really quiet but acceptable, hard starting when cold, perfect starting when warm.
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Old 05-23-2016, 02:21 PM   #7
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I've always disliked the four stroke twins and singles.

Had two of the old two cylinder two stroke OMC's "Light Twin" two cylinder engines. Water cooled w angled prop shaft lower unit. Very weedless props too but they seem to push boats fine.
The first two Evinrude's I had were too salted and would overheat. But I just bought a 4hp Light Twin (same engine w bigger carb I'm told) and it seems fine but I haven't ran a boat w it yet. Was pleased to get ot for $225. This one is a Johnson .. the others were Evinrude's.
Very light, smooth and quiet if not run near full throttle.
I think they are rebuildable and probably economically w the possible exception of the crankcase seal in the middle of the crankshaft. That's a weak link on all two stroke twins but rarely goes bad.
I think they are 33lbs. Many of these engines had folding lower units. They folded sideways so the prop ended up close to and perhaps a bit under the powerhead. In the day they came w an optional folding FG box that was much like a suitcase. Those are hard to find now though.

North Western Washington State USA
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Old 05-24-2016, 05:18 AM   #8
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As small one lung outboard does not make much thrust.

For no noise a simple DC trolling motor will have near the same thrust ,

and is never a problem with old fuel or starting for guests.
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Old 05-24-2016, 05:37 AM   #9
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The bigger issue with small displacement 4 stroke outboards is their sensitivity to ethanol fuel issues...
The jets in the carburetor of typical small 4 stroke engine are so tiny that any exposure to water will cause then to hiccup when running ethanol fuel. Ever find that you have to fill up with fuel on a rainy day? Our last Yamaha 2.5 would always have difficulty after filling even on a damp day!
Then if you leave fuel in the carb for any length of time...its disassembly time to make it run.

I got so disgusted with the reality of the ethanol/small engine performance issues that I finally went out and found a like new 3 hp Yamaha 2 stroke that was 14 years old! I paid too much, brought it home and changed the impeller, fuel line and spark plug. Now we have a motor that always starts in a pull or two every time, ethanol or no ethanol! It sure does burn fuel though!
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Old 05-24-2016, 05:54 AM   #10
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I love my Suzuki 2.5hp its quite little vibration and the lightest available starts second pull every time
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Old 05-24-2016, 06:00 AM   #11
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Have a Lehr 9.9 with electric start. Easy to start, seems to be reasonably quite, and the fuel doesn't go bad. Have a 1986 Mercury 6 two stroke with electric start that still runs great and is a little noisier.

Both only require one push of the button to start.

Did I mention they were electric start.


I'm tired of fast moves, I've got a slow groove, on my mind.....
I want to spend some time, Not come and go in a heated rush.....
"Slow Hand" by The Pointer Sisters
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