OX66 Rpm fluctuating 3500-500 then back

[Billst]

Hello;
I just ran out of my warrenty on a rebuild 1999 0x66 200hp yamaha, of course. While returning from fishing this last Saturday in a heavy sea 4-5 ft chop the engine began to very suddenly fluctuate rpm's. It would go from 3500 down to 500 and then return imedietitly to 3500. It would repeat this every time it seemed I came down hard on a wave. I backed of the rpms but it seemed the problem returned even down around 2800 rpms. Upon returning I thought maybe gas so I drained the seperator and then the filter and both looked very clean with no debri and no water. I need some help here if anyone has an idea, I was thinking maybe a grounding issue but I have not found any loose connections. So.. any ideas would be greatly appreciated.

Bill

 

[rodbolt]

Re: OX66 Rpm fluctuating 3500-500 then back

sounds like a clogged VST filter, not a warrenty item.
keep running it lean and it can pop a piston, also not a warrenty item.

 

[Billst]

Re: OX66 Rpm fluctuating 3500-500 thanks Rodbolt

Re: OX66 Rpm fluctuating 3500-500 thanks Rodbolt

Thanks Rodbolt,
I see other folks have the same problem. Can this be caused by debri in the tank or is this a problem with the ethanol in the fuel?
contacted the folks who rebuilt the engine for me and they had said that they would fix it for free. Its only got 26 hours on it after the rebuild. They also mentioned that it seems to be very prevelant in our area? Connecticut. They have changed several just in the past few weeks. Could be just conincidence but could it fuel related? Any way thaks again for the info

 

[rodbolt]

Re: OX66 Rpm fluctuating 3500-500 then back

its not the E fuel exactly.
its what E-fuels do when they sit and what they do to the hull fuels system, especially on 5+ year old boats.
and yes the marine technician govt stimulous program has done well for me the past 2 years.