Help Troubleshooting: 440 and 550 won't start when hot unless throttle opened fully - Page 2
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  1. #11
    PWCToday.com Is My Home Away From Home wmazz's Avatar
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    Re: Help Troubleshooting: 440 and 550 won't start when hot unless throttle opened ful

    Quote Originally Posted by manytoyman View Post
    UPDATE:
    after watching these carbs when the motor is turned off I discovered that both of them feed fuel (or air) backwards
    from the return line through the carb and back to the tank. Given 15 seconds or more they fill with air. I can see this in the fuel lines.
    There is supposed to be a restriction in each carbs return line.
    Each carb is nearly plugged off at idle because the restriction
    is only .013".

    But if your 440 has a 38mm 550 carb, the restrictor is missing.

    There is no restrictor in the 44mm 559 carb either.

    On both of the 550 carbs (38's and 44's) the restrictor is on the right
    hand side of the hull.

    The purpose of the restriction is to prevent the engine from
    running rich at idle. Otherwise the return line is not needed.

    After idle the engine consumes more fuel, and less (if any) gas
    returns to the tank.


    Bill M.
    Horsepower == Speed, RPM != Speed



  2. #12
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    Re: Help Troubleshooting: 440 and 550 won't start when hot unless throttle opened ful

    Thanks Bill. I needed to be more clear.
    The 85 440 has the OEM 38mm Mikuni carb that came with it.
    The 88 550 has the OEM 44mm Mikuni carb that came with it and rev limiter is present but I have not tested it.
    Question: is there a standard way of testing the restrictor in the 440s 38mm carb?
    I know I can blow air through the rev limiter to test the 550 and will do that shortly.

    Jim

  3. #13
    PWCToday.com Is My Home Away From Home wmazz's Avatar
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    Re: Help Troubleshooting: 440 and 550 won't start when hot unless throttle opened ful

    The return line on the 38bn 440 & 550 uses a banjo bolt for the restrictor.

    Remove the banjo bolt, and turn it upside down. Either there will be a small
    hole for the restrictor, or about a 1/8" hole for the 550 style 38.

    I know you said the 38bn was the original 440 carb, but from the outside
    they are the same, except there is a 1/8" hose fitting near the top right
    of the carb for the 550 rev-limiter.


    Bill M.

    I believe the restrictor size is stamped on the top of the banjo bolt.
    Horsepower == Speed, RPM != Speed



  4. #14
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    Re: Help Troubleshooting: 440 and 550 won't start when hot unless throttle opened ful

    UPDATE: took the 550 out yesterday for a test with the one way check valve mounted in the tank on the RES line. Perfect. Ski starts and idles now when hot. So if you have a hard staring ski when hot it might be worth a try. Certainly worked for me. The 440 is now starting fine on the trailer after installing a check valve in it as well. Will test this one when the river comes back down (rising from 4 to 20 ft due to hurricane remains coming through the area).

  5. #15
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    Re: Help Troubleshooting: 440 and 550 won't start when hot unless throttle opened ful

    Old thread UPDATE #2. A new year and the old problem returned in the 550. Takes 5 to 10 seconds of cranking to start when hot again. Grrrr. But get this: compression cold is 105 (both) which is apparently just enough to start a ski. However, when hot I just pulled a plug to check and low and behold it dropped to exactly 90 psi. My theory is this thing is getting hot and losing just enough compression to be a hard starter unless spun until it fires once or twice and the motor spins faster - and hence more compression to get it going again. The amount of time the starter spins it must be in conjunction with the right amount of fuel needed with a particular amount of air to fire at the lower compression. Just a guess.

    I have new OEM rings on the way and once installed I will test both and hot and cold to see what they are running.

    BTW - another interesting thing i witnessed when checking compression on a motor (650 this time) today at the water. I was reading 150psi cranking and then the other cylinder fired and the compression in the cylinder I was reading jumped to 180 instantly - thus confirming that once the motor starts (higher RPMSs) compression goes up significantly. At 150 this motor will start on a single cylinder but at 90 in both they won't start at all. Just what I observed today while testing a few of the skis.

  6. #16
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    Re: Help Troubleshooting: 440 and 550 won't start when hot unless throttle opened ful

    Update #3 - WSM rings have a larger gap in the cylinder than Kawasaki OEM rings. Holding them up also reveals there is a difference in size. Waiting on a new head basket before I can stick it back together.

  7. #17
    Top Dog JC-SuperJet's Avatar
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    Re: Help Troubleshooting: 440 and 550 won't start when hot unless throttle opened ful

    Dynamic (Running) Compression should be more than Cranking Compression. No contest between a 'Compressor" running at 600 rpm versus one running over 3000 rpms...

    90 psi Cranking Compression barely supports Ignition. Rings and Bore are worn. Pistons slapping. Getting Hot Exhaust Gas Blow-back into the Crankcase cooking everything in its path.

    Time for a Top End Rebuild.

  8. #18
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    Re: Help Troubleshooting: 440 and 550 won't start when hot unless throttle opened ful

    Update: I believe the issue is in part caused by a closed throttle plate and thus very slow idle. I didn't have my tach with me at the water yesterday but tried increasing the idle to see what the response to hard starting while hot would be. The initial findings are encouraging. I turned it up a bit and it would start on the second hit of the starter. I then turned it up a bit more and the motor seemed to start on first bump without any throttle from the finger. I then gave a quick check of the low jet and found that I got a smoother idle by leaning it out a little more. I ran out of time but think I am getting closer to this 550 starting better when hot. Will know after it makes it to the water again.

    I also have a theory that if the throttle plate is completely closed at idle then when the engine is cut at high speed the vacuum in the carb draws in a lot of fuel from the idle and circuit and also adds to the flooded (acted that way when starting hot) idea. So by opening up the throttle plate I might be getting a less flooded motor and a better fuel to air start mixture.

    More later.

  9. #19
    PWCToday Regular Carter.104's Avatar
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    Re: Help Troubleshooting: 440 and 550 won't start when hot unless throttle opened ful

    Wow nice job of getting to the bottom of it! If it’s in your budget I highly recommend getting a SBN44 and ditching the BN. It’s a night and day difference with tuning and overall riding. I got tired of messing with those temperamental BN44s.

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