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  1. #1

    Join Date
    Jun 2019
    Posts
    13

    Exclamation Help! Will not start warm in water!

    I have a Rotax 787 in a 96 SeaDoo. I have a very difficult issue and I'm trying everything. I can get the boat in water, take my time parking the car and such. Then with the boat sitting in water cold I can start it easily. No issue. I run the boat for any amount of time and it runs awesome. I'm getting 45MPH on choppy water and wind with a full tank of gas.


    However, when I get to the dock and shut it off. I can turn it on within a few minutes no problem. But, if I wait too long it will not start under any condition no matter what I do. It is literally sitting there cooling off and it will never start. I inspect the plugs and they never get fouled no matter how long I try to start it. I have a few small bubbled in the return lines, with seemingly no entry points because the fuels system was pressure tested, and when I'm trying to start it those bubble barely move at all. Like fuel is not being pumped.


    I've been over this so many times. Here's what I have done;
    • Replaced decrepit pulse hose with brand new reinforced fuel line hose
    • Carbs fully rebuilt with genuine Mikuni parts.
    • Pop off set to 35PSI in both MAG and PTO <- In Spec
    • High Jet to 0 and low jet to 1 full turn out
    • Idle set to 1500 RPM in water
    • Fuel lines all new, no green goop
    • Fuel filter brand new OEM
    • Fuel vent, selector and baffle inspected and perfectly clean
    • Fuel system pressure tested at 5 PSI for 15 minutes
    • Starter is good and using the 8 tooth gear (per seadoo) for more torque
    • Battery is brand new and fully charged with a smart charger. Grounding is also good
    • Compression at 140 PSI in both cylinders
    • Rotary Valve removed and inspected. Using solder method, per the book, I have clearance of .0125 when I measure the thickness of the solder <- In Spec. However there are lines in the valve, not deep but they are there. Nothing to catch my nail on. Does the valve look ok in the photos or is this blatantly bad even though the clearance is good?
    • I have spark on both plugs as tested with an inline spark tester
    • Spark plugs are a perfect brown so not fuel starved and not flooded
    • I've added a little fuel to the intake, as well as the cylinders themselves and it will not fire
    I'll try anything else at this point. Take away is I have good spark, good carbs, seemingly a good rotary valve, good compression and a clean fuel system. I am totally at a loss as to why this is still happening.


    Note: I don't know if this is normal, but I clearly hear a constant dribbling of water into the exhaust. It's as though it's coming in through the water valve or the exhaust box. But the exhaust pipe on the outside of the hull is angled upward so I think it would be tough for water to get in there. Regardless, I hear this constant dribbling like a faucet left on low and dribbling into a pan. Is this normal? Should water be dribbling into the exhaust when the boat sits in water? This seems off to me since it would be only a matter of time before the exhaust tank the tuned pipe connects to fills with enough water to bog out the exhaust.


    Please help and thank you so much in advance!!

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  2. #2

    Join Date
    Jul 2015
    Posts
    23
    is this a boat or jetski,sorry i missed that info

  3. #3

    Join Date
    Jul 2015
    Posts
    23
    im getting lost at the bubbles? did you change the brass seat in the carbs? they are 5 diffrent size byt at this point it could be anythig

  4. #4

    Join Date
    Jul 2015
    Posts
    23
    to try and narrow it down, when it gets to the point to where it wont start. hold throttle wide open while cranking,if after a minite or 2 it pops or starts, you have a carb prob

  5. #5

    Join Date
    Jul 2015
    Posts
    23
    but do not pump throttle.never do this becauseit has boosters

  6. #6

    Join Date
    Jun 2019
    Posts
    13
    I've been pumping the throttle and also holding wide open.

    However! Yesterday I got stuck at the dock due to a boat blocking me in. I had to shut it off and since I couldn't start it again I was stuck there waiting.

    So I took the time to track down why I was hearing dribbling only after running. It seems that the water regulator valve is leaking water into the resonator after the boat has been running. Enough that I can hear it actively dribbling in there.

    So, I was like screw it and I used my hose punchers to pinch off the hoses on the water regulator as well as the main water line from the pump to the engine. For the heck of it I tried to start it and IT FIRED UP!!!!

    This tells me definitively that water is getting into the exhaust at a high amount while the boat sits in the water and I can see anything that would cause this. That is why it won't fire up and once I pinch those lines off, it starts perfect. I did it again this morning to test it out and it works every time.

    So, now that I know why the boat won't start due to the water likely filling the exhaust, I need to figure out why this is happening.

    As mentioned, water is actively dribbling into the lower canister of the exhaust that's connected to the tuned pipe. And unless I pinch that off, as well as the main water line form the pump, I have no way to start it. Once I pinch them off, it start perfectly every time. There is absolutely an issue with the water getting in.

    Any advice on what to check would be great. And is water supposed to pour into the exhaust from the water regulator?

  7. #7

    Join Date
    Jun 2019
    Posts
    13
    I have been pumping it. I've tried that and just holding it wide open, as well as messing with the choke. Nothing did it. But, take a look at my most recent message. I found out that water is infiltrating the exhaust while the boat sits and it's causing the exhaust to bog and not allow it to start.

    No water gets into the cylinders, it's filling the exhaust to a point the engine cannot fire. I pinch the water hoses going to the water regulator, as well as the main one coming in from the pump and try it. After a few seconds it fires right up when it ejects the standing water from the system. I then remove the clamps and it start and runs without issue.

    If I run it, then shut it off letting it sit in water I hear water pouring into the exhaust from the water regulator. Right now, the only way I can get it to start again is pinching those hoses. But at least I've identified where the issue is, I just don't have a clue why this is an issue.

    Any advice?

  8. #8

    Join Date
    Jun 2019
    Posts
    13
    Quote Originally Posted by mikew15 View Post
    im getting lost at the bubbles? did you change the brass seat in the carbs? they are 5 diffrent size byt at this point it could be anythig
    Hi, yes, I did a full rebuild of both carbs with brand new genuine Mikuni parts and I also change the needles and seats with brand new Mikuni ones. I set pop off on both at 35PSI with on 5 PSI loss after popping and they both held 15PSI over night with zero loss.

    The inside of the carbs are pristine so I'm thinking they are ok. Plus the engine runs awesome and I can get 45MPH out of the boat on choppy water with a full tank.

    But when you have a set take a look at my other comment. It seems the issue is water filling the exhaust when the boat sits, and only happens when it's warm.

    Also, it's a 96 seadoo challenger. I didn't say that initially because even though it's a standard rotax 787, sometimes my posts get moved into the less common boat section that very few people even look at on a different forum. The mods move my posts and they just sit there and rot lol

  9. #9

    Join Date
    Jul 2015
    Posts
    23
    I had a feeling it was a boat. You need to look and make sure you installed the right seats. I had one here a few years ago almost drove me crazy. Carb looked new,long story short the guy put 4.0 seats in and he supposed to have 3.0. You really need to check this, they are calibrated for the size and weight of the craft. I have a 1998 twin sitting here now, dual 717 in mine, I don't have the water regulator on mine, I did notice seadoo made the exhaust higher than the exhaust pipe on these

  10. #10

    Join Date
    Jun 2019
    Posts
    13
    Thanks for the reply. I hav 1.5 needles and seats in there per spec and pop off is set. The boat runs perfect, and will start if I clamp off the water lines. It'll start in water cold even if I don't clamp the lines. But if I run it, and it's warm, when I stop water is actively pouring into the resonator through the water regulator valve and this only happens warm. This doesn't happen cold.

    I don't think my issue is any of the carbs or pop off, RV or compression. All of that checks out perfect.

    It's something with the water flow preventing the engine from starting when it's warm. Until I clamp the inlet from the jet pump it will be impossible to start. Once clamp it, and give it a few seconds to clear the water form the exhaust it starts.

    I have no idea. I don't think the water regulator should be pouring water into the resonator. But I don't know how to confirm.

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