1999 OX66 Weird Issue Yesterday

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johnnyboy

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Hey guys, took the boat out yesterday for a nice fishing run and noticed a little issue. When I was running at full throttle it seemed as oen of the engines would slow down quick, it seemed like the actual throttle pulled back and without me touching the throttles she would shoot back to the full throttle power. Can this be a throttle line issue? Could it be my fuel pumps couldn't keep up? Any advice would help thanks! :hmm
 
johnnyboy said:
Hey guys, took the boat out yesterday for a nice fishing run and noticed a little issue. When I was running at full throttle it seemed as oen of the engines would slow down quick, it seemed like the actual throttle pulled back and without me touching the throttles she would shoot back to the full throttle power. Can this be a throttle line issue? Could it be my fuel pumps couldn't keep up? Any advice would help thanks! :hmm
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Did the throttle lever actually move?

Usually if the VST is plugged, the revs will drop off at speed and kind of choke, not speed back up.
It could be Low pressure pumps but I am not sure. It could be a bad throttle position sensor. It could be a spark issue. Without more info it is difficult to diagnose.
 
I'd drop the VST tank and check the filter. Fresh gas? How many hours since the VST was checked? How many hours on the motor? Was it a cut-out sensation or did it throttle down quickly? It seems most problems guys are having with the OX66's are fuel related.
 
PLEASE let me know what fixes this issue... if you get it. We are having the same problem on our '99 225 and we have yet to figure it out.

Thanks!
 
I'm thinking the Low Pressure pumps. If you haven't changed them in several years, I would as they are not that expensive and the diaphrams inside do wear out.
 
I had the same problem, replaced the VST filter and low pressure fuel pumps, problem still occurred, replaced the O2 sensor and now my '97 250 hp 2 stroke efi Yami runs like new....
 
How much did you pay for the o2 sensor. Heard they were expensive. Mine seem to be working fine and engines run great. From what I know, changing filters, plugs and cleaning o2 sensor and VST are the major things to do. David
 
From what I've read, symptom of a bad 02 sensor is a high speed pulsating in the throttle, like quick throttle changes which may be Johnny's problem. There are several threads on boats.net about what the peak voltage should be.
 
nitrox32 - Did you have to replace it? I was told to just clean them once a year.
 
I replaced it, the mechanic said it was in need of replacing since it was the original one and it had never been cleaned before. It was really carboned up.
 
I've tried cleaning them. Soaked them in Sea Foam up to the threads overnight but never got much carbon off them. I guess they just go bad after awhile
 
I was told to soak only the tips of them in Ring Free and clean them once per year. Mine still seem ok.
 
Had similar issue last year on my 1998 OX66 250. Got up on plane, up to speed and engine would drop off about 1000RPM, got progressivly worse to the point where motor started stalling at idle. Changed out 3 low pressure pumps, runs like new.
 
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