mercury 25hp 4 stroke blowing bubble

[gazza2007au]

i have a mercury 25hp 4 stroke 2000 model when i run the engine in my drum at idle i get a lot of exhaust coming out of the prop i checked on youtube for the same models and everyone elses engine of the same model dont blow any bubbles out of the prop is mine normal?
http://www.youtube.com/watch?v=RE_YGOoHA-0

 

[sutor623]

Re: mercury 25hp 4 stroke blowing bubble

Dude is this for real? Is the motor a through the prop exhaust?