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Old 19-12-2012, 19:54   #1
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5 hp 2 stroke running rich

I've been having trouble with this engine not making enough power for a while. Other then that it has been very reliable just not making the power it used to. Now it barely goes above idle and fouls the plug after a few minutes. I'm thinking that the reed valve isn't opening all the way causing the power issue and now the running rich problem.

Any ideas?

Thanks, Mike
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Old 19-12-2012, 20:05   #2
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Re: 5 hp 2 stroke running rich

I assume this is an outboard. And the fuel mixture is correct? Its not oil injected is it? Does it have high and low speed screws? And we can go from there:-)
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Old 19-12-2012, 21:25   #3
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I assume this is an outboard. And the fuel mixture is correct? Its not oil injected is it? Does it have high and low speed screws? And we can go from there:-)
Yup, a 10 year old Nissan (Tohatsu) outboard. It has an idle mixture screw which has always been one turn open. I assume the mixture is too rich, but the jets aren't adjustable.
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Old 19-12-2012, 21:53   #4
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Re: 5 hp 2 stroke running rich

Quote:
Originally Posted by mikefossl View Post
I've been having trouble with this engine not making enough power for a while. Other then that it has been very reliable just not making the power it used to. Now it barely goes above idle and fouls the plug after a few minutes. I'm thinking that the reed valve isn't opening all the way causing the power issue and now the running rich problem.

Any ideas?

Thanks, Mike
I do not think the reed valve would cause plug fouling. Is there black smoke? With a very rich mixture the hydrogen in the gas will burn, but not the carbon, so black exhaust. Is there gasoline on the outside of the
carburetor? A stuck float valve will have gasoline overflowing the carburetor bowl. The engine will also sound more like a 4 cycle than a 2 cycle.
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Old 20-12-2012, 05:31   #5
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Re: 5 hp 2 stroke running rich

I'm not sure if or how this might apply to your engine (I don't know it specifically), but a failing diaphragm in the fuel pump could be sucking raw gas into the engine. There is pulsating pressure in the crank case of a 2-stroke, and that pressure typically drives the fuel pump. A cracked diaphragm in the pump, and with each suck of the crank case, in comes some raw gas which then gets sucked into the cylinders.

The other more obvious thing would be a stuck float valve in the carburetor. I'd probably check that first. Often you can just remove the air intake cover and look down the throat of the carb. If you see any raw gas, then the carb is likely the source.
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Old 20-12-2012, 06:15   #6
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Re: 5 hp 2 stroke running rich

The float height should be set so that the float is parallel to the carburetor casting when the carb’ is inverted. Hold the carb’ upside down (bowl removed). The float should hang exactly parallel with the carb’ body. Adjust by bending the tang ever so slightly.

Because the carb’ bowl is almost always completely full when running, the shutoff point (float height) is all that really matters.
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Old 20-12-2012, 07:13   #7
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Re: 5 hp 2 stroke running rich

A carb rebuild kit for your motor includes a the needed parts for the fuel pump. Pull the carb off the clean everything well, Blow out all the small passages with compressed air Assemble paying close attention to how the old fuel pump diaphragms were oriented.
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Old 20-12-2012, 22:19   #8
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I'm guessing a carb rebuild kit is in my future. I'll post back after I finish.
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Old 21-12-2012, 01:24   #9
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Re: 5 hp 2 stroke running rich

Don't know about the 5 hp, but the Tohatsu 3.5 carb has a tapered pin that meters the fuel as you open the throttle. Replaced mine, and the engine ran better than when it was brand new--leaned it right out.
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Old 21-12-2012, 02:12   #10
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Re: 5 hp 2 stroke running rich

I you sure it rich.

My Yanmar 5 HP is a great workhorse, but a clogged carburettor is a common problem. Despite filtering fuel. I get a loss of power, it usually starts, but has no power or stalls when its put in gear. This happens about every 3 months. I can now remove clean and reinstall the carb in about half an hour.

I think the problem is that with these small outboards the fuel passages are so tiny they clog easily.

Be sure to at least clean both the carburettor jet and the needle valve that let's fuel into the carb.
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Old 21-12-2012, 04:54   #11
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Re: 5 hp 2 stroke running rich

Also, be sure to use gasoline that has no alcohol. The alcohol takes moisture out of the air into the gasoline that makes for poor running, and the shelf life of the fuel is about 3 months even without the moisture. I add fuel stabilizer when I fill the tank and that is supposed to make it good for a year, it says.
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Old 21-12-2012, 06:52   #12
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Re: 5 hp 2 stroke running rich

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.
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Old 21-12-2012, 10:56   #13
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Re: 5 hp 2 stroke running rich

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Originally Posted by noelex 77 View Post
I you sure it rich.

My Yanmar 5 HP is a great workhorse, but a clogged carburettor is a common problem. Despite filtering fuel. I get a loss of power, it usually starts, but has no power or stalls when its put in gear. This happens about every 3 months. I can now remove clean and reinstall the carb in about half an hour...
Do you mean that you have a filter between the fuel tank and the carb? I put a fuel filter on my 1.2 HP Johnson and never had a problem.
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Old 21-12-2012, 11:18   #14
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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.
Willing to bet it is this ,if not it is likley that the needle set jet is bad or or clogged...
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Old 21-12-2012, 13:01   #15
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Re: 5 hp 2 stroke running rich

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Do you mean that you have a filter between the fuel tank and the carb? I put a fuel filter on my 1.2 HP Johnson and never had a problem.
Yes it's got a fuel filter in there, but the debris still seems to get through ( its just a fine nylon mesh). It clogs the carb not the filter.I always filter the petrol when filling the tank, and the engine gets run most days 365 days a year.

I have just purchased a larger fuel filter and I will add that to fuel line in the hopes of solving the problem .
Sooner are later I going drop some carb bit over the side when giving it a clean.
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