My engine has been running rough for about 2 years now (since I owned it) My Yamaha mechanic says that since that motor drops out cylinder #1 and #5 at speeds of less than 800rpm's....it will run rough.

Does anyone know that to be true? My hinges sometimes vibrate and my lowrance unit shakes a bit when i'm going less than 800rpm's...however, when I get it over 800rpm's it tends to smooth out.

Here is a pic of the boat and motor:

I've got a 2003 150 HP OX66 and it has always run a little rough at low speed but I've had no trouble with it. I've changed the plugs but did not help. This is the first I've heard about it dropping 2 cylinders. May be true. I'm curious also.

biggest issue Ive had with the ox66 is the O2 sensor gettin dirty. make sure you run some Yamaha Ring Free with your gas to help it stay clean.

I don't know if the 150HP does it...but yea, the 250 drops #1 and #5 at less than 800rpm's for fuel conservation.