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  1. #1

    1200 Engine Diagnosis

    Hi All,

    Had some bad luck in the Keys last week and managed to drop both rear cylinders in my 99 LS2000. On the way out to the reef the starboard motor shut down at around 5200 RPM. Was able to restart and found that it wasn't cutting out immediately, it was losing RPM and would actually stay running if I throttled down. Did this 2 more times and then everything seemed normal. At the end of the day we were coming back and then the same thing happened on the port motor! Exact same situation, different motor. I was hoping it was just a fuel issue or something but when I got home and checked the compression both rears had around 30 PSI. The port engine is an SBT with around 40 hours on it, bought it last September but got it installed back in March. It is now back with them awaiting teardown. I tore the starboard engine down today and here are the pics. I would appreciate any armchair diagnosis that can be offered, need to know the best option to get this motor running while I wait for the other warranty replacement.

    I had redone all of the oil lines and rebuilt the carbs last season so I don't think it is that, but this engine always smoked more than the other. When I pulled the airbox off the front carb seemed to have a lot of oil around it.

    Thanks for the help!
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  2. #2
    mudslanger's Avatar
    Join Date
    Jul 2010
    Huntsville Al
    First you need to find what caused both engines to fail. Was this the first time the engines were run since they were worked on. did you have good gas or last seasons gas in them. did anyone put flame arrestors on them, did anyone adjust the high and low screws on them. also make sure your oil is not contaminated and is flowing freely to the carbs. also check to see if the check valves on the oil lines are flowing or the arrow is pointing to the carbs. if they have them.

  3. #3
    I had put the other motor (SBT) in back in March and have been running the hell out of the boat ever since. Back in July there was a 4 week stint where we didn't get to use the boat, took it out to make sure all was good before the keys and it ran great after replacing a battery cable. Wednesday of last week it ran perfectly with no issues. Filled up with marina gas (possible issue??) and then right off the bat Thursday AM the motor in the pics started dying at high speed. So, nothing had changed from the time that it was running well to losing them both. Boat is completely stock. I had set the carbs per factory manual after rebuilding them last year.

  4. #4
    You should of ran premix

  5. #5
    Moderator RX951's Avatar
    Join Date
    Apr 2005
    League City, Texas
    Sounds like an oil line came off.

  6. #6

    Join Date
    Jan 2006
    Texas City, Texas
    Those piston tops look black (baked on oil) and dry (lean) with a little bit of pitting (detonation). Throw in some poor quality marine gas...... I'm thinking HOT HOT HOT.

    What do the heads look like? Are they pitted?

  7. #7
    Oil lines are all intact. I would love to run premix but unfortunately with boats you end up with angry passengers when going downwind in no-wake zones. I got some pictures of the head, cyl 3 is pitted. Some more background: when I bought the boat as a project, this engine wouldn't start and I found it was filled with oil. When I took off the carbs to rebuild I had to vacuum out a ton of oil from the crankcase through the intake. You can see the other 2 pictures show sludge seeping out from near the flywheel. I also found the stator covered in oil when I pulled the front cover. Do the check valves prevent oil from going into the motor or just prevent the oil from heading back towards the tank when the engine is off? Seems like more oil than usual is being used in cyl1, but not enough in cyl 3?

    Another factor is I don't usually run the engines at above 6K, so there could have been a problem for a while that just finally surfaced - as you suggested, the lean condition.
    Thanks again - this is very helpful.
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  8. #8
    Yamaha artisan Cutlass's Avatar
    Join Date
    Oct 2010
    Madison, WI, USA
    I thinking possibly the marina gas was bad and maybe the engine detonated or backfired and that might have blown out the rear crank seals. That would make the #3 cylinder run lean and overheat....but that doesn't explain the pitting in the head.

    Is this grease coming out of the case halves of the engine? The picture is zoomed in so far I can tell where on the engine that is.

  9. #9
    Yep, that is where the case is joined under #1. Looking back, I have had a leak there for a while so while it needs to be addressed I don't think it's the cause. Is it possible the pitting is from a previous incident? When my other motor went the head looked like that but there were chunks of piston missing. In this case I only see scoring. In any event, I'll be splitting the case and doing new crank seals. Just hoping the bearings are ok and I can get away with top end only.

  10. #10
    slothman's Avatar
    Join Date
    May 2011
    I agree with salty, crappy marina gas = BOOM

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