4-Stroke Engine Smoking

[Blackbird]

I have a pair of 2005 Yamaha F250 4-stroke engines that have been almost trouble free. I always have them serviced by a professional mechanic each fall. Since the last service, I noticed a very short puff of white smoke at start up after they sat for about a week. After the puff they ran fine with no more smoke. Recently, the engines sat for about 3 weeks. When I started them, one engine belched enough white smoke for about 30 seconds to make a 2-stroke owner cringe. The other engine smoked for about 5 seconds. I check the crankcase oil levels and they were both right up to the top. Any other Yamaha 4-stroke owners ever seen this problem? What was the root cause. I'm interested in all the info I can get before I call my mechanic.

 

[Lt.Mike]

Blue smoke that hangs is oil burning. White could be moisture or a slight over rich condition from a choke or a slightly flooded engine. If its excessive it may be an injector and or fuel pressure regulator issue.

 

[Doc Stressor]

Most likely one or some of your injectors are leaking. They hold fuel under pressure when the engine isn't running. Have a tech do a leak down test. Mine does the same thing when I don't run it every week.

Leaky injectors can lead to oil dilution and accelerated engine wear.

 

[Lt.Mike]

Yes Doc thanks. I wasn't going to give this example for fear of giving you an unnecessary panic but I had this issue with my Chevy pickup with the 5.7 vortec engine. The fuel regulator went bad and over pressurized the injectors on one side of the motor bleeding through after it was shut down. That created a fuel lock (hydro lock) in the rear two cylinders and cracked the block when I went to fire it back up. That cost me the price of a new long block, $2500. The sad part was it ran perfect right up to when I parked it for the night. The next morning it was locked
If you google it you'll see its a common failing for the chevy vortec 350 motors. Could your outboard be doing the same thing? I don't know but its worth getting it checked out, injectors and the pressure regulator.
Good luck with it.

 

[Blackbird]

Thanks guys. Injector problems are where I'll start. The smoke did not smell like oil (actually little odor) so I suspect it is fuel related.

 

[Lt.Mike]

If you do find that the injector(s) is bad, don't ignore the fuel pressure regulator! If the injectors are bad it is probable that a bad regulator caused the injector to fail.