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  1. #1

    Lean Runaway kicking my *%&! on a 1200 non-pv

    Ski rides and idle fine on the water. When it is dry and on the trailer it will run away when u run it briefly to flush the water out of the exhaust.

    What HAS already been done: Removed carbs and exhaust, blocked them off, charged through 1 unblocked Pulse line to 10PSI. Dropped 1psi over 15min. Carbs were freshly rebuilt with Mikuni parts, pressure tested (40psi through fuel inlet with all other ports blocked off and outside sprayed with windex to look for bubbles. No bubbles or drop in pressure. Then popoff was set to 55psi and highs/lows set to shop manual spec for the 1200. All gaskets for the carb base, carb top, stainless steel plate on top of the carbs and the gasket under the flame arrestor look great and have a very thin layer of grease to help them seal.

    I took it on the lake and set the idle to 1400 on my tiny tach and turned out the lows a bit till it stopped bogging out of the hole.

    This is a stock setup except for blockoff plate and primer kit.

    Is it possible that the low speed jets are simply set up too close to the bottom of the threshold and just need to be opened up a bit more to fatten up the fuel to air mixture?

  2. #2
    I failed to mention that this "runaway" can be stopped by pulling the lanyard or pressing the stop button every time. The pulse lines are new and tight as well so no leak there. Also, I did fiddle with the idle and was able to make it go away on the garden hose but the hose was not even turned on hard enough to do much more than get a burp of water out of the pisser now and then.

  3. #3
    1 psi over 15 minutes is a sealed engine. You mentioned in ur second post that pulling the lanyard and the stop button will shut it off. That leans me to believe it is not an airleak. If it was it would not shut off by the methods you described.

    As far as the cause I'm not really sure. How far does it rev to out of the water? Does it keep going until u stop it?

  4. #4
    She revs right up past 5 or 6k. I always kill it as it is climbing. I have noticed it before doing that off hose and out of water but now that I significantly lowered the idle into the no load range of about 1500 and then raised it to about 2500 only under a medium garden hose doesn't climb any more (on hose). I don't know if it will climb when dry fired again with this new idle setting but i will bet that it won't even idle under a full water load when I get it to the lake. Originally, I turned idle to about 3k on the trailer and then when I put it on the water it wouldn't idle so I turned it up further on water till I hit 1400...but that is when I first noticed the runaway. I just wonder if this lean condition is in my carb settings since I have beat this dead horse to death elsewhere with diagnostics. I'm just glad it is this ski with the big hull opening and not this damn XL I have been rebuilding ha!

    One place I have not been on this engine so far is the reeds. Is there anything like this that could result from damaged reeds? Maybe it took a backfire and blew one up?

  5. #5
    Oh yea...if it matters for this question...the compression is quite low at only 95 each but even across. P.s. there was one leak while doing the pressure test...I use a chunk of fuel line with a golf T stuffed and gasketed into the end to seal my pulse lines off. When I was spraying the case, there were little bubbles coming out of the top of the wooden T. Guess it was made with very porous wood ha!

  6. #6
    Yamaha artisan Cutlass's Avatar
    Join Date
    Oct 2010
    Madison, WI, USA
    I think this a combination of the low compression and idle speed setting. With the lower compression, it has lower power output. And it seems like you need to open the throttle blades more to make enough power for it to idle in the water. But with the carb throttles opened that far, it revs really high when its on the trailer (no load).

  7. #7
    caliburn's Avatar
    Join Date
    Aug 2012
    Bethany, Mo.
    If you want it running right ,do a top end rebuild on it. If ever I have a ski that drops 20 Psi Or more from what it should be I am rebuilding it ASAP

  8. #8
    Caliburn and Cutlass,

    Both good input! I started thinking about the compression issue and thought I would add that since it is the only other thing that seemed to be out of line that I had not thought through. It certainly has been affecting my hole shot because it just slips out of the hole slowly till it builds enough speed at high RPMs to drag this 1000 lb SUV out of the H2O...but I never really though much about additional impact.

    Top end job it is. I have new mis-ordered pistons laying in the garage and a new head gasket anyway. Might as well take advantage of this cooler 90 degree garage weather ha! Will report back but it may be a couple weeks on this one.

  9. +1 by:

  10. #9
    Superman! fivespeedsteed's Avatar
    Join Date
    May 2010
    Midlothian VA
    lean runaways cant be killed with the lanyard or pressing the stop button. i always thought a true "lean runaway" was when it was dieseling and just reving on its own. i had one after i cleaned out a carb, and i pulled lanyard, pressed stop, pulled plug wires, and disconnected battery and it was still going.

  11. #10
    I had read your post on your runaway previously and was thinking about how i would be freakin out looking for my phillips head screwdriver to take the battery out ha! I recently built and sold a 98XL1200 and told your story to the buyer after I sold it to him so he would know to dump the throttle if it ever happened for any reason. Seems to be the only quick way to kill it if it has a primer setup. Oh well, clearly it is time for a top-end job anyway so apart she comes. I wanted to wait till I got my other SUV up and running clean before I pull this one apart though. Hopefully the cylinders are good or just need a light cleanup. IF the pistons look good...does it stand to reason that this thing may just need new rings to bring the compression back up? I would assume that is the first thing to go in an otherwise healthy cylinder. For all I know this thing may just be out of tollerance for clearance due to a previous owner's cylinder cleanup.

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