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2019 Yamaha 2.5HP 4-stroke - smoking at WOT and dropping fuel

brettmarl

Regular Contributor
Engine is F2.5SMHB and has only seen 10-20 hrs of use. I use it to just putter from beach to our mooring ball and so mostly it is running at low RPM. It pees strong and starts and sounds normal-ish - maybe a tad rough.

Today - I ran it hard - maybe 90% throttle for a few minutes, and it started smoking (I think white smoke, but could have been blueish) - smoke seemed to be from inside the cover and idle silencer on the upper shaft. I hit the kill switch and turned off the fuel. Went to start it again and when I turned back on the fuel cock a small amount of fuel leaked out of what I assume is the carb overflow outlet - not a huge amount - maybe a tablespoon but enough to make a large sheen on the water.

After a minute - it started up again fine, and was OK on low throttle, but higher speeds gave the same result.

My first thought was the t-stat might not be opening... it looked pretty clean and I tested it - and it opened 3mm per specs in the service manual at 140F.

Oil level looks good - I haven't pulled lower off to look at impeller yet, but suspect it's fine as it's peeing so well.

It's probably still under warranty but I'm a long way from a dealer, so would prefer to self diagnose if its something simple.

Any other ideas of possible things to look for?
 
Try running sea form in it, check the spark plugs. 20 hours at putter speed will build up carbon.

roger that. About to run it with some sea foam. I also noticed that the oil was over filled. I guess on the 2019 they changed to viewing window to having a dipstick on the oil cap. If I read oil when cap is strewed in - it’s over filled for sure - and about max mark when the cap is inserted without engaging threads. Drained and refilled oil to proper level.
 
Problem solved - was oil overfill for sure. Runs much better and ran it at WOT for 5 minutes and was happy as a clam. Guessing the seafoam helped a little too, but think that oil was main culprit.
 
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