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  1. #1

    Help on how to run a new engine!!

    Recently rebuilt the 780 Blue Fuji motor, top end wise.... jugs,pistons. I've built many car engines but never a watercraft engine. How can I get water to the engine while on land? This is a 96 Polaris 780 SLT stock. Thanks to BlueFishCrisis here on this forum my carbs are done Awesome work KUDOS to you and you're work and time to share to others.


  2. #2
    BlueFishCrisis's Avatar
    Join Date
    Aug 2011
    Medina, Ohio, United States
    Break In Procedure This really should be done in the water under load. You can install a hose adapter on the water rail in place of the brass plug to connect there. The other option is to remove the hose at the water inlet and temporarily install a fitting to connect your hose. Either way, be sure to start the motor first, then turn on the water, turn of the water when done, then shut down the motor. The cooling system is technically an open design. If the motor isn't runnning, it can flood from the hose feed.

  3. #3
    Click avatar for tech links/info, donation request K447's Avatar
    Join Date
    Jul 2007
    near Toronto, Canada
    Why do you need to run the engine on land with garden hose water?

    Engine break in requires a water load on the impeller, which means the hull needs to be floating.

    I shall assume the engine is in the hull and the watercraft is fully reassembled. Checking engine alignment to the jet pump is a separate question.

    You can run a cold engine for 20-30 seconds at a time without any water. Then let it cool before doing it again. This is usually sufficient to verify that the engine will start and run, respond to throttle, etc.

    You can run the engine with garden hose water cooling for a couple of minutes at a time. This limit comes from the water seals in the driveline, which are water cooled when the hull is floating but are exposed to friction heating when running on land. If the jet pump and drive shaft are removed then you can run the engine on the garden hose for as long as you want,

    There is a hose connection method called reverse flush, but the preferred method for consistent engine cooling is as follows. Find the large 3/4" water cooling feed hose connection. This is on the right side (when looking down from behind the watercraft) of the jet pump base, just inside the hull. When the watercraft is floating and running normally this is where the pressurized water from the jet pump enters the hull to cool the engine. Remove the hose from the water tube end, then connect a 3/4" hose barb to garden hose female adapter.

    Now the garden hose is providing the exact same water cooling to the engine as the normal water flow.

    The required sequence for using a garden hose is;
    Engine Start, THEN turn the water on. No big hurry, you have 10-20 seconds to get the water flowing.
    You do not need huge hose water pressure, just enough to flow through the engine evenly.

    When you are finished, ALWAYS turn the water off FIRST, then briefly burp the throttle once or twice to blow excess water out of the waterbox, then shut the engine down.

    This sequence prevents possible water back flow into the engine core from the exhaust system. The exhaust gases are cooled by direct injection of water spray into the exhaust flow. When the engine is running the exhaust flow pushes the water out through the waterbox, which is why you will see water coming out the exhaust hull fitting.

    Pro tip: Keep the hull tightly strapped to the hull front and rear, then back it down the launch ramp until the jet pump intake is fully submerged. Take the seat off.

    Now you can run the engine with water load on the jet pump as long as needed. You can observe everything inside the hull, check for leaks, proper engine temperatures, etc. You can apply throttle, check steering, etc. make sure there is no debris or rocks under the jet pump intake, and set the parking brake in the tow vehicle.
    Last edited by K447; 07-19-2014 at 11:24 AM.

  4. #4
    Thank you guys for the information, these tips will definitely help me get it on the water this week, when job and time permits.

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