Misfiring 2003 115hp 4troke

Mulle

Recruit
Joined
Aug 31, 2009
Messages
2
I am new to this forum and have looked for a similar experience but have not found one...so here goes my story.My motor has 75 hours of run time. At about 50 hours it started to misfire at both high and low speeds. By increasing the rpms to 4-5k it would clear up and run well for some time. This year it started out great but after about an hour of operation it started misfiring. High speed cleaned it up for a bit but now it misfires at all speeds including idle but starts well. When looking at the plugs there is no real evidence of a fouled plug. I have repplaced the plugs and moved them around without success. Does the intermittent action weigh towards electrical or fuel? Thanks for your help in figuring out my mystery motor.
Mulle
 

BOAT DOCTOR

Petty Officer 2nd Class
Joined
Jun 3, 2009
Messages
120
Re: Misfiring 2003 115hp 4troke

it sounds like fuel i would take a look in the vapor tank they have a small filter on the bottom of the fuel pump something cold be floatting around in there and clogging it
 

eng241

Cadet
Joined
Aug 30, 2009
Messages
8
Re: Misfiring 2003 115hp 4troke

Is this motor electronic fuel injection or carburated?
 

Mulle

Recruit
Joined
Aug 31, 2009
Messages
2
Re: Misfiring 2003 115hp 4troke

Sorry for not providing more detail. Motor is a 2003 Yamaha 115hp 4cyc with fuel injection.
 
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