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I just got a used boat with a 40HP 2 stroke Yamamha outboard. It hadn't been used in a few months and ran poorly when I got it. I did a shock treatment of seafoam, and cleaned the carbs with carb cleaner spray directly into the air intakes. I checked to plugs for proper gap setting. It runs ok now and starts on the first pull, but doesn't develop full power. It has a few times, but only for a few minutes, then the RPM's drop to about half and its back to running its normal poor performance. What could be the culpret???
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wlowe,
Since the shock treatment did temporarily make a big difference, I think the problem is still with the carbs. Probably some gum/varnish flaking off and plugging up the jets.
I would remove the jets (high speed and pilot) and squirt carb cleaner directly into the orifices. Also, remove the drain plugs on the bottom of the carbs if you have that kind. Inspect the high speed jets o-rings and replace if cracked or distorted.
If the above does not do the job, then I would remove the carbs and clean and install a carb kit.
Also, you may have gotten some bad fuel with that used boat. You may want to drain and start with fresh.
Also, depending on age and number of hours, you may want to replace the fuel pump - some owners do this as routine maintenance every 4-5 years.
Make sure all filters are clean.
You need a Yamaha shop manual to guide you along with the above procedures - can order online at www.yamahapubs.com.
Good luck, and let us know how you come out [img]smile.gif[/img] ,
Ken K -
I was able to get some carb cleaner directly into the lower portion of the carbs via removing the drain plug screws (brass screw/hex bolt type object). Unfortunately, 2 of the bolts had stress fractures and the head of the bolts broke off from the rest of the bolt as I was removing them. Had to special order some replacements. But after replacing them, WOW. My old top speed is now my new high idle speed. I knew that motor had soo much more to give.. On my 16' flat bottom, that 40 really moves.Comment
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