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Honda outboard four stroke misfiring?

I have a mid 90's Honda 25 four stroke. I had 3 new carburators installed and adjusted by a vacuum gauge as well a new thermostat, sump oil and gear oil changed. I also had them install a fuel/water filter. They did a compression test and that checked out somewhere above 200? The repair shop said it was good to go. My problem is as soon as the motor warmed up, it started popping and lost power and I could not give it any more power than just above idle speed, it just felt like it was running on fewer cylinders?

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I would take it right back to them. It is possible that the fuel lines were not changed or at least flushed before they put the new carbs on. It must have been in bad shape if you had to replace the carbs. Although, sometimes that is cheaper than a carb job.

If is very possible that some debris left in the fuel system or fuel pump that is caught in one or more of your carbs. It only takes one on a 25hp to make it run bad.

This sometimes happens even if the lines were flushed. I see it every once in a while. We try to catch it before it leaves by running it under a load at the water for a while to be sure everything is working right.

Since you put a water separating fuel filter on, it appears that there was a problem with water. Again if lines were not flushed, water could still be in the lines.

Before you take it back, drain each carburator into a glass jar and see what the fuel looks like. If it have water or debris it will settle to the bottom. If you find some, just flush the system until no more water or debris comes out. Then see how it runs.

You should always use some sort of fuel treatment like PRI-G or Sea Foam to keep the fuel fresh and to minimize the effect of the ethenal in the fuel.

Hopefully, the dealer can find the problem fast and at least give you a break on cost. We would normally do it for free if the customer brings it right back and it appears that we missed something.

Posted on Sep 17, 2009


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