[TomS]

1999 200HP Yamaha 0x66

I just went over 110 hours this season on the motor and completed the following maintenance:

Checked fuel rail pressure @ 35psi
Checked TPS baseline voltage @ 5.04V
Checked throttle valve synch
Adjusted TPS sensor to 5.00V w/ throttle valves closed
Checked O2 sensor output @ .6-.7V
Changed Racor fuel/water seperator
Changed spark plugs
Adjusted oil control rod to stop w/ throttle valves closed

Plugs looked ok, with a few small carbon 'balls' loosely attached. O2 sensor is new this season, no carbon build-up on it, but the outside of the draw tube was filled in with Carbon. I soaked in RF and scraped it off. I always run with Yamalube and Ring Free.

While running the O2 sensor diagnostic with the test harness (boat in water), I noticed that the voltage swung between .6V and .7V. Blocking the hole on the top throttle valve would cause the voltage to swing, but not in the .3-.9V range as I expected. I noticed the same behavior this spring when commissioning the outboard and after installing the new O2 sensor.

Before service, the engine was idling a little rough, but no problems getting above 5k RPMs, WOT was around 5600K. Noticed that when I run the engine tilted way up idling out of dock area, there is a lot of extra smoke when I trim the motor back down. One cold morning the engine actually stalled a couple of times after trimming down.

After service, engine sounded stronger at idle, probably due to clean plugs. Fuel/Water seperator had absolutely no water or debris.

Ok, enough history and on to my question.

My usual start-up routine is simply to turn the key for 1-1.5 seconds, no problem. A couple of times before and after my service I have turned the key the same way, but the engine wouldn't start after maybe 2 seconds. I would turn the key again and it would start right up, no problem, and would never have problems starting throughout the rest of the trip and repeated starting/stoppings.

To paraphrase Rodbolt - what is my engine telling me?

-- Tom

[rodbolt]

your numbers are high on the O2 sensor.3 would be very lean burn and .9v indicates rich.
what method of fully closing the throttles did you use, the only proper way is to unclip the throttle links.
when you covered the hole in #1 throttle plate you should have seen .8v or higher and it should swing lean when uncovered.
check your lift pumps,vapor seperator filter and spark plug caps.

[TomS]

Rodbolt,

I used your method of unclipping the throttle links for both the TPS and oil control rod adjustments.

Forgot to mention that I replaced the fuel pumps (2) and inspected/cleaned the VST filter at the beginning of the season.

The only item on the Rodbolt 0x66 hit-list that I wasn't able to do this spring was check the spark plug cap resistance. For the life of me, I couldn't get the caps to come off. Is it possible I have a version where the caps and wires are a single piece?

In any case, since I don't know the previous maintenance history, does it make sense to replace them since its been at least 200 hours (and likely much longer)?

-- Tom

[rodbolt]

the caps unthread from the wires