running rough at idle

[the dog house]

My ox66 250 hp 2001, started running rough and smoking at idle..after you get the boat above 1400 rpm it smooths out and runs fine...i primed the fuel bulb when it was running rough and it didnt change anything..
i checked the mv signal thru the ox sensor and it was fine..i cant believe it has a plugged filter because it runs great at cruising speed...any ideas would be great...it also smokes and shakes at idle speed..

 

[John_Madison CT]

IMO, anytime you have a problem with an Ox66 it's time to do some basic maintenance, all which is pretty simple.

1. Replace your VST filter.

2. Thoroughly clean your O2 sensor along with "dogbone".

3. Replace your Low pressure fuel pumps.


If after these are done, and you still have a problem, then you can look into other stuff.

 

[DaleH]

Agreed ... here's how to clean the O2 sensor:

www.boatsetup.com/O2sensor.pdf

 

[the dog house]

thank you for the input...i drained alittle fuel out of the vst resivoir and it was clean...should i still clean the filter..i took the sample after it sat over night..

 

[John_Madison CT]

Yes, replace your VST filter. It may look clean, but it still can be clogged with microscopic particles.

 

[the dog house]

ok.i just couldnt belive it would run well at full throttle if it was starving for fuel..but i appreciate the input...i will take it apart...thanks

 

[the dog house]

Thanks for the help,cleaned the vst and and o2 sensor the engine smoothed out..there wasnt much debris on ethier but must have been enough...

 

[TimC2520]

Here is a photo of the re-designed vst filter. It's not cheap, but if you want to replace it, it should filter more gunk than the original which will hopefully give you more time on the water.

 

[Megabyte]

Given the symptoms (rough at low speed and OK at high speed) I would suspect the low pressure fuel pumps, but what do I know? I leave such things to my shop as they are much more talented than I.

Also, doesn't the OX66 drop a cylinder (or two) at low speed by design?
What control that behavior?