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Vmax SHO running poorly

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Jimmyd

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I am looking for some advice.  I have a Yamaha vmax sho 115 on my Bennington.  Winterized the motor and added stabilizer to the fuel.  Here in Ontario Canada it sat for nearly 8 months.  51 hours on the clock.  It fired right up out of storage and burned off the fogging oil.  First run was great for about 5 minutes.  Suddenly it shuddered and wouldn't go over 3400 rpm.   Back to the dock.  Added octane boost, changed the fuel water separator and waited a day.  Boat still idled rough, and could only get to 4600 rpm.  Fuel consumption was deplorable.  I then removed  all but 5 gallons of fuel and added 13 gallons of fresh 91 octane with ring free.  Still runs very rough at idle but smooths out at 4000 rpm but max rpm is 4800.  Should reach 6000. Am I on the right track with fuel?  Change plugs? Fuel filter? 
 
Plug wires tight?  Your description sounds like a cylinder isn't firing...
 
kaydano said:
Plug wires tight?  Your description sounds like a cylinder isn't firing...
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Kaydano


Thanks for the advice.  I removed the plugs to inspect.  There is a coil pack on top of the plug socket which are held in place with two bolts, so unlikely I think.  Bottom plug has some carbon deposit unlike others.  Poor plug maybe?  A few bucks worth a shot?
 
I would certainly check the fuel filter if you haven't done so yet.  Clogged injector maybe?
 
Last edited by a moderator:
If it was mine, I'd change the plug. If it persists, take advantage of the warranty. 
 
My guess is ecm....sounds like it's in the limp home mode. Please let us know the outcome.
 
Sounds like good old water in the fuel. I know you removed all but 5 gallons and added some fresh fuel but there's still water in the tank. Add some "water removal" in the fuel product and let it run.........
 
BigKahuna said:
Sounds like good old water in the fuel. I know you removed all but 5 gallons and added some fresh fuel but there's still water in the tank. Add some "water removal" in the fuel product and let it run.........
Click to expand...

+1. Sounds like water to me as well.
 
Update - noticed the motor was making oil and dipstick smelled like fuel.  Pulled plug 4 and it was wet with fuel.  Replaced the plug with a new one and changed the inline fuel filter as well.  Idles like a champ.  Will water test it in next few days.  Stay tuned.  Thanks to all for the help and suggestions!
 
I would also change the oil and filter.
 
Thanks for letting us know!  Glad it was a cheap and easy DIY fix.
 
I just replaced the plugs in my pwc after putting it in this weekend and it running like crap. $6 bucks later and three new plugs it runs like new. Glad you got it figured out!
 
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