You learn something new every day. After 6+ years of sailing Sowenna in various waters the outboard, a Yamaha 50hp 4 stroke decided to play up and was only firing on 2 cylinders and regularly cutting out which made it interesting in getting back to the marina.
I called the local marine engineer over and his initial assessment which turned out to be accurate is that this model does not have a 'stopper' and it is easy to lower the motor too far in which case water gets in and messes up the carbs. He suggested he could fit a stopper, so he did, or I should remember to leave ONE bar visible on the display monitor.
Simon Armitage
Sowenna 26M
In 18 years and thousands of sea miles never had this problem.
Something to watch out for on the 50 HP Yammy is the engine up-down switch . I have had two failures of the engine mounted switch ,jamming the motor either up or down. This switch is in ‘parallel ‘ with the console mounted switch affecting both switches not operating. The trick is to disconnect the motor mounted switch.The console switch will then work. Replace the motor switch when when convenient-they are rather expensive.
Strange diagnosis! The difference between correctly trimmed down and "as far as it will go" can't be more than a few degrees. How that difference could be responsible for throwing water into the air intake is hard to fathom. Maybe if it's over-trimmed it throws up more spray (though usually the converse is true). The air intake should be well shielded from spray anyway.
Being able to trim hard down is useful for getting up on the plane, as it helps lift the stern.
It's not something I've ever heard of!
Rick Jones (Treasurer), former 26X & 19 owner, Isle of Wight
Very strange! The air intake on most outboards rises through a serpentine bend to allow spray to drain rather than be drawn on to the air filter. The filter will in turn stop small quantities of water and allow it to drain before any water can get to the carbs.
Outboards on RHIBs get hit with a lot more spray than on a Mac and don't seem to suffer.
I'd suspect more likely to be longer term salt corrosion of the aluminium in the carbs and/or perished rubber parts (as is a common issue).
Good servicing ought to prevent both being a problem but we all know finding good servicing is akin to finding an honest politician!
On the subject of the Power Tilt system. I modified the wiring so that failure of the engine mounted switch or relay wouldn't stop the throttle mounted system operating
Power Tilt_0
Dave Newton Sailbadthesinner
Ive had a misfire problem for ages - tried all sorts of things. My engineer is currently fitting new solenoids which he is convinced will solve the problem (at least I hope so!!). Apparently there are two, one for the top two cylinders and one for the bottom two. The advice is to replace both since if one is ok it probably wont be for long.
Mine was misfiring at higher revs and latterly cut out at low revs but agree with Rick and Dave -doesn't seem to make sense that trimming angle should allow water in
Rod
Check for leaks around water pump.
My outboard was fitted by Macgregor U K . Had no problems as described. I believe that the amount of tilt is determined by the fitter.
We had what seems like a similar misfire issue last year with our 50hp Yamaha (‘05 carb version not the later fuel injection). At first I thought we had a flooding carb issue as we had a slight fuel leak on one of the carbs but when we replaced the drain screw ‘O’ rings it stopped the leak but made no difference to the rough running. We stripped down the carbs cleaned them and replaced the float valves as well as checked the solenoid valves to no avail. So the second time round we replaced all the ‘O’ ring seals on both the inlet and outlet to the carbs and it made a massive difference and removed the misfires completely. The tickover is now stable and the engine runs a lot more smoothly throughout the rev range. You can sometimes see if there is an issue by using a set of manifold vacuum gauges as the will be unstable if there is an air leak.
If you decide to change the seals don’t buy the Yamaha spares as they are massively expensive - you can buy the same ‘O’ rings much cheaper from Polymax on line full set with lots of spares for under £20. The engine appears to be very sensitive to an air leak on the manifold. The solenoid valves only operate whilst the engine is heating up so the engine wont tickover when warmed up if there is a problem with these. Hope this helps.
Mike C 26M
Hi Mike,
I don't suppose you have a note of what you ordered from Polymax? (sizes, material etc) I am seemingly yet another another Yamaha 50 user that struggles with a misfire. Changed quite a lot so far, but not those particular O rings.
In fairness, I don't get much opportunity to use and fix our 26X just yet - but I could do with it working for the Big Mac!
David
David Kirk
26X Glissando
Dumfriesshire, Scotland
Thanks for this, Mike. I shall pass it on to my engineer
Simon
Pages