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  1. #1

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    Sep 2014
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    Yamaha LS2000 2 Stroke, Only hitting 6K RPM at WOT

    I wanted to see if you could help me diagnose an issue that I am having. The issue is that my starborad engine is only hitting ~6000 RPM's at WOT while it used to go to ~7000 and the port engine continues to hit 7000. Also, while it gets to 6K RPM, it bounces a bit around 4500-5K and not the same as the Port side. I know that this is the powerband but it is bouncing in this zone versus skipping this range like it used to. I have been getting great advice from others but I continue to hit a wall:

    Now the details:
    - boat is an LS2000 with twin 135's.
    - I rebuilt the starboard carbs last season. I also redid the jet pumps including the impellers on both sides using remanufactured impellers and new impeller ducts.
    - I have the fuel/air separator pump from GroupK and this was already installed last year when the engine was working. There are 2 fuel lines from the tank that feed a single T union/coupler which then goes into the pump as a single line. The pump then has a single line out to a T union which feeds a separate line to each engine.
    - I have Sierra fuel/water filters vs. standard OEM filters. These have always been in place and I replaced the filter as part of my troubleshooting. No change
    - compression is the same across all cylinders (99) and both engines. While 99 is low, I expect some of that is my gauge and I am dismissing this a bit since the port engine reads the same and it hits 7K RPM.
    The starboard engine should hit 7000 RPM and I want to address the problem.

    1) I changed the impellers/pump drives to see if it was an impeller issue and the problem continues. Not the pumps/impeller. Could it be the intermediate housing "limiting" the RPM's due to friction or a bad bearing??
    2) I checked compression and it is consistent across all cylinders and both engines. While it reads 99 on the cylinders, I expect some of that is the harbor freight gauge and the good engine is at the same compression and it still hits 7K. I am thinking it is not a compression issue.
    3) I put in new plugs and did a plug test. All cylinders appear to be running based on the color of the spark plugs. I am not sure if there could be a misfiring problem though, i.e. plug wire, CDI?
    4) I thought the carbs could be the culprit since I rebuilt the STBD (problem engine) side last year. I swapped out the carb racks (Arghh... at least 4 hours) between both engines and the problem continues on the starboard side and the Port engine continues to run at 7K. Not the carbs
    5) The engine hits +7K RPM when it is out of the water and on a hose. ???

    What would you do to troubleshoot this? Ideas?

    - Would a bad spark plug or cap cause this? It hits 7500 RPM off the water so that may be an important point
    - Reed valves? These are over $300 for a set so I want to be careful about just replacing them. Not to mention the work to pull the carb off again....
    - CDI or ECU? How and what???

    Thank you


  2. #2
    Prism's Avatar
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    May 2007
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    Exactly which engine is in this boat? 65U is a non powervalve 1200, 66V is a powervalve 1200 and 60T is a 1300 engine. What year is the boat so we can figure out which engine we're working with if you're not sure. A misfire could cause the rpm bouncing around and usually will run in the 4-5000 rpm range with a miss. A powervalve issue can cause this as well....not sure which engine came in your boat. One way to check for misfire is to run the boat cold up to wot for about 30 seconds. Then shut it down and feel each cylinder and exhaust manifold ports to try to find an unusually cooler one. While you're in there, compare the exhaust pipe temp from engine to engine near the wide section of pipe. If the pipe is a bit hotter on the engine thats not performing correctly, you may have a cat converter that has deteriorated and clogging the exhaust. Let us know what you have/find.

  3. #3

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    Sep 2014
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    This is the non powervalve 1200 engine. It has the 1200, 135 HP yamaha engine. It is a 2001 Yamaha LS2000. Thank you and I appreciate any and all help!

  4. #4
    Prism's Avatar
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    Its been many years since I've dealt with the 65u 1200 engine. Maybe someone else will chime in with some other ideas. Do the boat engines have catalytic converters? It might be a wire or coil issue as well. You could swap parts from one engine to another (coils, plug wires, plugs, etc) one at a time to see if you can isolate a bad part.

  5. #5

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    Sep 2014
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    No, this boat does not have catalytic converters. I hope someone can chime in with some things to look at. I don't think swapping the plug wires and coils is that easy but I will check on that. Another person also recommended swapping the waterboxes. That is on the list but I am still waiting on other ideas as well.

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