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Thread: Motor issues, please adivse

  1. #1
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    Default Motor issues, please adivse


    My boat has been really hard to start this winter. I didn't own it a year ago so I thought this might be normal. When I run the boat for any length of time at idle, the combustion chamber loads up and the plugs get fouled. I have a Clymer shop manual for my motor, a 2 stroke carbed 115 Yamaha. I have the mixture screws (I think that's what they're called) set more lean than the manual suggests, but she still burns real rich. Time before last when I went out, she was missing occasionally so I put a new set of plugs in before I went last time. That seemed to fix the problem. I haven't used the boat in 3-4 weeks and Slabprowler and I went fishing yesterday...


    Since it had been hard to crank and since the river was flowing mightily, I wanted to crank the motor before we unhooked the boat from the trailer. I pumped up the bulb (it never stays tight between trips but it's new and so is the fuel pump) cranked up the motor and it cranked quickly and it let out a huge cloud of smoke. Much more than normal. It spit, sputtered and "coughed" (backfire maybe?) several times. I'd run up the warm up lever and it would pick up RPM's but never smoothed completely out. We unhooked the boat and headed out. I pushed down on the throttle and very little happened. The motor didn't sound right. To me it didn't sound like it was running on all cylinders. We limped along and got to where we were gonna fish. We fished a while and I wanted to head back before dark, in case we couldn't make it back against the current. We made it back, but it took a while.

    The motor under load would never get over 2000 RPM's. If I put it in neutral, it would tach out and sounded pretty normal. While under power, if I pushed the throttle over half way, the motor would choke down and shut off.

    I have not checked all plugs for spark so I know that will tell more. I just wanted to see if this sounded familiar to any of you and what you think it might be? I think it could range anywhere from something very simple and inexpensive like new plugs and cleaning the carbon out, a coil, to a CDI box, or even a hole in a piston....

    Any idees?

    Cray, you're the troubleshooter, what's wrong with it?

  2. #2
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    tlefire is offline Crappie.com Legend * Crappie.com Supporter
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    Have you cleaned the carbs? Sounds like one or more are gummed up.
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    Sounds like one or more high speed jets are plugged up. First thing I would do is pull carbs and clean real good. Don’t run wire through jets. Use small enough mono through them. Spray them good with some carb cleaner. When you get it back together look up carb link and sync on YouTube. Go through that procedure. Then adjust jets to where they are supposed to be. I would also go with another sent of plugs. After that if it’s still not right you can trouble shoot back on electrical side but sure sounds like carbs. By any chance have you done a compression check on this motor? If not I would suggest doing that also.
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    I bought this CD Manuel and it is the way to go. Don’t know what year yours is but this one covers everything.
    YAMAHA OUTBOARD SERVICE REPAIR MANUALS - 2000-2001-2002-2003-2004 All Motors | eBay
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    Thanks for the info. I did a compression and a leak down test on the motor when I bought it last winter. I haven’t done one since. I’m going to dig into it after lunch and see what I can find

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    Ok, so it’s fixed but I’m not 100% sure what fixed it. It was firing on all 4 cylinders, so I took off the carbs, tore them down and cleaned them. No funk seen. There might have been a speck in one jet or it might have been a drop of gas. I don’t know. I cleaned all jets with carb cleaner and an air nozzle. Adjusted the carb floats to the correct height then I put the carb back together, reinstalled it. Took the plugs out that I had put in a couple weeks ago and replaced with new ones. The old plugs were loaded up with oil but after running a mile or two with the motor not running right I expected that. Wanted it up, sprayed it down heavily with Seafoam top cylinder cleaner, let it sit 10 minutes and cranked it back up. The smoke was incredible. Took it to the river and she runs like a top.

    So here’s all I changed:

    1) Adjusted floats to corect setting. They now allow more gas into the bowl.

    2) Connected a spin on cartridge water separator that I had installed in the boat but never hooked up.

    3) Readjusted mixture screw exactly in Yamaha specs. I had previously tried to “lean” down the fuel mixture by adding more air.

    The boat probably ran better than it has since I’ve had it. Very little smoke.

    Here’s the strange part. I picked up 300 RPM’s at idle and I did not adjust the idle screw.

    I dont know any more than I did but my boat is running great. Maybe one of you can tell me what I changed that made a difference

  7. #7
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    Float adjustment is critical on 2 stroke motors plus carb adjustment. Leaning out a 2 stroke is a recipient for disaster.
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    I know leaning it out is dangerous, but I've kept a check on the plug color and it has always run too rich. Maybe the float adjustment was the problem.

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    Plugs show that the mixture is still too rich.

    Ideas???

  10. #10
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    Is it one plug or all and can you get a good picture of plugs.
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