Help me figure out where to start with this one. Last Sunday we were out on the lake. The motor started up and ran fine all day long……. Until I opened the throttle all the way up. I figure I had not opened it up much this summer and Sunday was a great day. When I opened it up all the way the engine ran fine for about 30 seconds, then I noticed that it was running really rough. I was still getting my full RPMs, but it was noticeably rough. I ran it all the way back to the dock like this. When in idle I could tell it seemed to be missing on one cylinder some if not most of the time. Is this the dreaded carb issue related to the Honda bf50 or do you think it is something else? The boat is on a slip so I cannot do any serious diagnosis work easily.
When ever I out in new fuel, I always put in fuel stabilizer and on the advice of the last marine mechanic to work on the Honda I also run the engine with the fuel line disconnected to completely empty out the carbs (every week). The fuel tank did not seem visibility dirty inside when I filled it last. Spark plugs were new at the beginning of the season.
I've had similar problems. The carberated engines really want to run full out, not idle around. I make it a point to try to run flat out at least 10 minutes prior to pulling into dock. Your other methods are also helpful. My recommendations (have worked for me in the past) are:
1) Run a fuel additive - Yamaha Ring Free Fuel Additive seems to be the best (though it is insanely expensive ($28/quart)) - mix 1 quart bottle in 1 gallon of gas and run at high speed until dry.
2) Pull out the plugs and clean as they are likely pretty fouled up.
3) Repeat #1 and #2 about every 25 hours of engine run time.
