2000 Yam 200 VMAX rough spot

[vortex]

Can anyone tell me where to start with a rough patch between 4000 and 4400rpm. Motor starts fine and revs to 5000rpm as sweet as could be. But between 4000 to 4400 rpm the revs won't hold constant like a fuel shortage. Also smoking a lot at idle (500rpm) even when hot.When I rev above about 1200rpm the smoke clears. I am running with a Racor in line filter/separator (10 micron).<br /><br />Motor is an OX66 Vmax giving me 55mph with a 19" prop on a Rigid Inflatable boat at 5000 rpm.<br />All help appreciated as no highly skilled maintenance techs available in my part of Ireland.<br /><br /><br />Mark

 

[rodbolt]

Re: 2000 Yam 200 VMAX rough spot

hello<br /> try cleaning/testing the O2 sensor and replacing the low pressure fuel pumps. order the test harness for the O2 sensor. remove the air box. attach the test harness and a DVM. whith the engine idling cover the air bypass hole on the #1 throttle plate. you should see a rapid rise in voltage. remove the finger and it should drop. you should see a normal reading of somwhere between .35 and .7 volts and a constant scaling up and down. also unscrew the red plug caps from the wire leads and rest them with an ohmeter. should see about 5K.<br /> the pumps and O2 sensor as wellas checking the caps should be part of routine maint. been my experience of at least once per year or 200 hours on the O2 sensor cleaning. someplace on this forum Seahorse has posted a good procedure. you will need the O2 sensor removal tool and a torque wrench and the holder gasket kit. has the High pressure pump fuel filter ever been cleaned? thats at least a yearly as well. and the correct factory manual is a must.

 

[vortex]

Re: 2000 Yam 200 VMAX rough spot

Rodbolt,<br />Thanks for the expert info. You have given me enough work for a while so I will let you know how it goes. While the rest of Ireland is celebrating St.Patrick's Day i'll be at my motor!<br /><br />Thanks,<br /> Mark

 

[rodbolt]

Re: 2000 Yam 200 VMAX rough spot

good luck<br /> at least I have never had a hangover from working on st paddy's day