Yamaha 2001 225 OX66 random quitting at idle - The Hull Truth

ilovewindydays · 05-25-2008, 09:05 PM

I have a 2001 225 OX66 that has 1500 hrs on it.
It quits randomly at idle with a bit of a pop or burp. Some trips it does not happen at all . Sometimes it wont start after being turned off for 5-10 minutes but will restart after sitting for a few minutes. It also seems to load up a little when trolling.
Where should I start looking?
thanks

A1 Outboard · 05-26-2008, 05:51 AM

A pop or a burb usually signifies a lean condition which could be from restricted injectors, possible air leak into a crankcase, cold running, weak pumps, or even vapor lock with today's alcohol laced fuels. With 1500 hours on the motor and an unknown service history, the first thing to do is a compression test to make sure all the cylinders are within about 15# of each other. Then do a complete decarbonizing procedure with Yamaha's Combustion Cleaner, Merc QuickKleen, or Evinrude Engine Tuner.

Yamaha has a history of weak fuel pumps so unless they have been changed recently, replace them, and check the fuel system from tank to motor for any loose clamps, soft hoses, or anything that could cause air leaks while the hose is under suction.

Make sure the thermostats are making both cylinderheads run about 140°F and it would be a good idea to clean out the O2 sensor and tube and check the operation. There is a factory sequence of snchrozing the throttle plates and linkage, and setting the throttle position sensor, get it done using the factory manual or a trained professional.

There are recirculation valves and hoses that should be inspected if all else fails, and in extreme cases, the injectors may have to be sent out for cleaning.

ilovewindydays · 05-26-2008, 06:36 PM

I checked th compression at 105-100 psi each. The O2 sensor and tube were all clogged up with carbon. I cleaned it and re-assembled it. I am planning on new fuel pumps after my next trip out.
Could the clogged O2 senson been the cause?
thanks,
Scott

A1 Outboard · 05-26-2008, 10:32 PM

That could be part of it but it affects the motor at all rpm ranges.

http://www.boatsetup.com/O2sensor.pdf