Yamaha 225 OX66 Rough Idle After Prop Change

[stf]

Last week I changed my props from 3 Blade to 4 Blade Mercury Rev 4s. After the change I have noticed that my Idle is much rougher sometimes. Since it is only sometimes I am going to assume that this has nothing to do with the props. Since I really like the performance change of the props in general I would like to start to troubleshot the idle issue. BTW I have not tried butting the 3 blade Saltwater series props back on yet to see if I still idle rough. The boat runs fine except during idle and when excellerating from 1200 to 1500 rpms. Just a little rougher than ususal. Once you get up past 2000 rpms everything is fine.

Initially I thought that I may have fouled plug and I may start out with just changing all of the plugs. I have changed the plugs this season already and have put about 50 hours on the new plugs. Not sure if I am wasting my time with this. The thermostats are about 2 years old now which I am thinking about changing as part of troubleshooting. I know if the engines run colder than normal rough idle is one of the issues. I also could check the poppit valve which I changed 2 years ago when I did the thermostats. I changed it for the newer part #.

The Oxygen sensor and VST filter were serviced 2 years ago. Which I am thinking about doing in the spring again. There are several places that I can start and I just do not want to waste time or money starting in the wrong place. The Low Speed Fuel Pumps were changed last summer.

Also, if anyone knows where I can get the Oxygen Sensor Crowfoot that would be great. I would like to be able to handle this service myself however I do not have the special wrench.

Thanks Guys!

[ghost28]

I have found Rev4s to be a bit on the clunky side when idling around especially on yamaha 3.1 liter motors....i have one on my personal merc 250 and i find that if i just drop it in gear and let it idle it feels as if the prop is out of balance or the PS is bent but then as i give it throttle it smooths out and then once on plane its fine....

before you go trouble shooting the motor try the old props on it first so your not wasting your time....

[stf]

Yeah, Good Call I guess I should try the old props before I start messing with anything. I wonder why the 4 blade has such an impact on the idle operation...