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Old 22-12-2012, 19:25   #16
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Re: 5 hp 2 stroke running rich

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Originally Posted by rrranch View Post
On ANY small 2 stroke with these symptoms its almost always exhaust related. If they can't get exhaust out then they can't make power and act like they are over rich. Hopefully you haven't done anything else yet so check the entire exhaust passage for obstructions. Physically. Not just by seeing bubbles or seeing the smoke. I'd take it apart and look. I fix this all the time on other 2 strokes like chain saws with dirt dobber nests or other crap in th emuffler. EXACT same symptoms. I just fixed it on an old outboard like yours too. The exhaust was so sooted up it was plugged.
I took apart the lower end and was able to inspect the exhaust passage from the cylinder to the prop. Definitely dirty but no obstruction to speak of. I'm guessing this wouldn't be causing the motor to run rich. Back to a carb re-build?
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Old 26-03-2013, 19:26   #17
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Re: 5 hp 2 stroke running rich

I overhauled the carb with a kit and replaced the main jet. Wow. The engine runs like new. Actually I wouldn't know that but it certainly runs better then is has ever before. Now it gets the dinghy (Achilles 8.5 ft) on a plane in seconds with two up and I can back off the throttle and keep planing. Woo Hoo!
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Old 05-12-2015, 23:13   #18
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Re: 5 hp 2 stroke running rich

Had similar problems with my merc 5hp (same motor). Scouring the web hard to find answers. Here is what I found after banging my head against the wall for the next "googlers".

The problem is rarely exhaust blockage. It may happen but I've never seen it although mentioned all the time with obs and chainsaws. That would be an outsider.

The 4/5hp model requires a rubber plug covering the idle jet. Many times a hack rebuild leaves this off thinking it doesnT belong there. It doesn't look like it should be there.

A worn bowl gasket will cause fuel to be sucked directly into the block. Massive flooding. Common problem and this was probably your fix. Ripped diaphram will also cause this.

Test your float valve and gasket by lightly blowing air into fuel pump inlet. Rightside up a little air, carb upside down no air.

Also, check recycle hose and valve (yes, theres a little check valve in the line). One way to cylinder only with no leaks.

If it runs even poorly with fuel all over, its probably NOT ignition related, although many posts have you running around checking it.

Good Luck
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Old 06-12-2015, 05:51   #19
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Re: 5 hp 2 stroke running rich

Greetings and welcome aboard the CF, Kraski.
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Old 06-01-2016, 15:04   #20
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Re: 5 hp 2 stroke running rich

With that Yamaha 5hp I bet it's got a steel tank ? That's the problem. I changed my steel tank to a plastic one and have had no further problems


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