Yamaha 9.9 hp high thrust 4 stroke engine electrical problems.

Sat 20 Jun 2009
In this video report, I take on a problem with my port side Yamaha 9.9 hp high thrust 4 stroke engine. A favoured engine with the light weight cruising cat class, this one has worked faultlessly for over 2 years, having been bought 2nd hand.

I had not that the engine had been a little rough at idle of late, and done the obvious thing of upping the idle! I had also noted the rev's wavering in the days before failure.... The next thing one morning she would not start.

Luckily, I have two of them and did not immediately worry about the loss of her, as we would get to the bottom of it.

99% of problems are with fuel as we know, so I checked fuel flow to carbie, drained it, checked flow off the fuel pump (located on the back). Next point of call was the spark plugs. It was quickly determined that there was no spark ... and that is no good.... The engine would turn over, so it was gettin 12V to the starter.... I then chased through the various electrical components, swapping with gear from the starboard motor. In the end I noted an open circuit on what I think is call the stator, which generates a current to drive the engine's CDI.

After pulling the flywheel, I was able to swap this with one from a 3rd engine that had stopped some time ago and ended up at the mates place.

I was spot on. With the stator replaced, I was back in business. Look for a 400 odd ohm resistance in the blue and brown wires that come from the stator for a win.

Watch the video for more information