Black Smoke from Yanmar

[bcguy]

I have a rebuilt yanmar hm 27 hp 3 cyl... bought it re-built 5 yrs ago. Most of my running is slow speed and I notice little smoke. Recently I had to go full throttle for about 3 minutes and noticed a lot of black smoke. I had heard that the engine should be run at near full throttle until the black smoke blows itself out. Is this correct?

... thanks

[neilpride]

You right, Yanmars like hig revs , not low . Also at low revs for long periods you risk to glaze the liners and pistons, causing blowby and blue smoke.

Check the condition of the air filter first, probably injectors to, and run the engine at full to burn all the carbon deposits , asuming you are ok in prop pitch , clean bottom etc...
Cheers...