Yamaha Ox66 Power Issues Please Help!!

Guys, when you say the low pressure fuel pumps, are these the primer motors mounted in the bildge area after the diverter? or is there another pump somewhere that I should be checking?

Thanks,

Joe
 
Negative, they are primer pumps and take the place of primer bulbs. You have 1-3 low pressure fuel pumps depending on the size of your engine.
 
Yeah my issue turned out to be the low pressure fuel pumps...I also had my vst cleaned and a few other things...can't say exactly what it was I took it in last fall and had Yamaha do the work. Thanks to everyone for there input..this site has been a life saver
 
Looking at what the did from Yamaha, remind you that it was last yr done all in one shot so pinpointing the actual cause could be hard. What may have caused the symptoms. I had a 2nd inline fuel filter, it was small, round in clear between the fuel water seperator and the engine. It was prob put in there from the privous owner. Yamaha said it was useless so they removed that, it could have contributed to the issue. They replaced all the low pressure fuel pumps. They also changed the filter on the electric fuel pump (VST) and clean the bowl. I recall the tech said something about a part of the vst actually came loose and was at the bottom of the bowl that may have been plugging the line when at higher rpms and drawing fuel it may have retricted the flow. They also cleaned the O2 sensor. Also I was having no oil being drawn into the engine reservior from the aux tank, these engines seem to cut out when there is not enough oil in the actually engine reservior as a precaution. They replaced the pump in that as well. I had this happen this summer already when I was low on oil. I simply cuts out / stumbles, thankfully I carry an extra 2 gal of oil, filled it up and off i went problem free. I did find that simply filling the engine reservior wasnt a fix since the sensor for low oil is actually in the aux reservior. I cant say exactly what it was but all said and done I have not had any issues since then. Sorry I should have updated the day I talked to the tech to have a better idea of what exactly they did.
 
this sounds like a vst filter issue. Time to change the vst filter. this is a common issue for a lot of people myselft included. Had the same issue: 4800rpm the motor would knock down to like 4200 then it wuld be ok. its a fuel dilivery problem at high rpm which 9 times out of 10 is a vst issue
 
I just dug up the invoice from the work I had done, under the resolution section "replaced fuel pumps, removed VST and found filter in bottom of bowl, replaced filter on electric fuel pump, cleaned bowl, installed oteiker clamps on fuel lines to fuel rails, removed and cleaned 02 sensor."
 
The HP fuel clamps did not have to be removed to check the VST. If the HP pump filter was loose laying in the bottom of the VST there's a good chance you injector screens & pressure regulator screen is dirty. If the motor is running good, great! Now I would definately replace the onboard 10-micron Yamaha fuel/water separator with a 2-micron Racor.
 
There is a float switch in that oil resevoir that hangs up. you may notice the problem if you bang over a wave. Also check that wiring harness.
 
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