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Old 05-12-2007, 11:53 PM
  #11
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What are the fuel pumps like on those motors. The older OMC pumps would fail and just fill the lower 2 cyliders with fuel. Would idle find but wouldn't pull under load since the plugs would just get washed out.
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Old 05-13-2007, 08:50 AM
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George - Wish I could find a qualified Yamaha tech to work on them. The one I tried knew less than I do. The good mechnic I had found moved out of the area I've heard some good reports about the shop on Kent Island, but I have no way to get the boat there (no trailer and they have no water access), and their on-site tech was booked a couple months out making it pretty unusable. It has the spec plugs, checked and all but one was burning right one (one had some carbon foul, found the idle screw on that carb was too lean). Also replaced all the plug caps last year as found a couple that had gone bad. I'll look at the manual and see if checking the stator is something I could undetake or not. I've rebuilt the carbs before, but I can see fuel coming from the high speed ports this time, which was the problem when they clogged before.

First Gun - The carbs were drained for the winter storage to prevent them gunking up.

Garry - There are 3 pumps per motor, they were replace about 50 hours ago. I don't realy have a good way to test them. The mechnic who found a bad pump then has left the area, and I'm having a hard time getting anyone else with a good reputation to call me back.

-Greg
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Old 05-13-2007, 10:10 AM
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Ok, here's my attempt at checking timing advance. Even though I have a Xenon, battery powered timing light, it's still very hard to see the timing marks in the sunshine.

Both motors: I thought I'd use the inductive pickup to check that the coils are firing first. The port side cyls 1&3 (can't get my pickup down between the cowling to try the bottom cyl) will trigger the timing light. The stbd cyls 2&4 won't trigger the light at all (??). Motors were unloaded at 2000 RPM. Seems strange, but again the stbd behaves fine and it shows the same as the port, and the stbd is running fine. The motors do not sound like they are missing, so I can't figure out why the stbd cyls won't at least trigger the timing light.

at 2000 RPM the timing is at TDC. If I slowly raise the RPM to about 3000 the timing still is at TDC +/- a degree (it's really hard to see the marks). If I just blip the throttle I can see the timing move to 2-4 deg off TDC to the (-) timing mark side (but that is the short side of the scale and only goes to 10, it is the opposite direction that I would expect since the (+) side of the scale goes past 20). for a second or two, then it returns to TDC. The stbd motor movement is pretty smooth, the port motor is very erratic and jumps around a lot.

Maybe one of the sensors to the timing compter is bad or has a bad connection? I think there are 3 thermostat switches, a crank trigger, and according to my manual a knock sensor. I'll see if I can find any test specs for any of them.

-Greg
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Old 05-13-2007, 10:52 AM
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Greg,
It is sounding like an advance problem.. one way to check if it is fuel.. Saw a guy do this 30yrs ago.. Ran the motor with the cowl off and used a squirt can with gas and oil mix.. shot it right into the carb.. When he hit the one that wasnt working.. it made power.
In your case a shot of fuel in the carb might give some response.. But if I rememeber from my outboard days.. the timing should move around more than just a couple of degrees.. ???
if you have a knock sensor.. you should be able to see the timing retard when you tap the block.. I would think..
I hate when there isnt anyone in the area that has knowledge.. good luck with it..
are there any OB sites that may have more info? ..

D*ck
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Old 05-13-2007, 12:21 PM
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try scream and fly.......A lot of outboard freeks there......
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Old 05-13-2007, 02:44 PM
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Tried Scream and Fly with problems in the past, not many Yamaha guys there. If I knew how hard it was going to be to find good Yamaha service outside of FL I would have bought a boat with Mercs. If someone made me a good deal on some used 250/300 Mercs I'd switch just because I do know some good Merc mechanics in the area.

-Greg
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Old 05-15-2007, 07:45 PM
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If I were smart I'd give up, but I'm too stupid/stubborn so I keep trying to find something wrong that I can fix.

I found specs/tests in my service manual for some of the sensors that feed the timing computer, so thought I'd try to check them.

thermoswitch - my motor doesn't have anything with the wire color codes shown in the manual or in the location shown in the manual (nor does it have the style connectors shown in the manual, most of the CDI connections are bullet connectors not molded plug connectors). There is a boss there, but it was never drilled or threaded. On to the next sensor.

throttle position sensor - it was replace a couple years ago, but tested it today and it shows in spec.

crank position sensor - couldn't get to the connector without removing the voltage regulator and starter relay and didn't have that much daylight time left so let it pass for now.

knock sensor - my VDM doesn't record low enough voltage to check for 200 mVAC, but I could see the measured resistance change as I tapped the sensor so it is generating some signal, just can't tell exactly how much.

Since it has so hard to see the timing marks in the daylight before, I decided I would try to check the timing again last night as it was cloudy and getting close to dusk. With the darker conditions I could see the timing marks much clearer, and the timing was pretty stable. I had it in gear under load this time instead of free running like before, being very carefull not to fall off the boat as it still moves around some even running on the lift with the props just submerged. Idle timing and timing near full RPM were on spec at -7 and +18. It clearly was advancing today as I hit the throttle, and coming back to retarded as the RPM dropped back to idle.

It is "possible" that unplugging and replugging the sensor leads might have cleaned a bad connection. It is "possible" that it is behaving randomly (I really don't believe in or trust electricity). But, maybe the "fuel problem" guru's were right. I bought a stand alone tank on the way home today and filled it with gas, so hope that (weather permitting) I can try that on Wednesday. I ran out of light to test it today.

-Greg
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Old 05-19-2007, 02:06 PM
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Garry,

Next time I don't listen hit me in the head a little harder. I finally decided to try changing the fuel pumps (had tried about everything else) and even though they are only a couple years old (and not that many hours) the middle fuel pump has a hole. You can cap the outlet and blow in the inlet and hear the air coming out the diaphram driver port.

I hope to get out on the water later to day to test it again and make sure, but I'm hoping that is the (only) gremlin.

Thanks - Greg
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