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  1. #1

    Is it bad for the ski to run out of gas before switching to the reserve tank?

    Is it bad for the ski to run out of gas before switching to the reserve tank? I was just wondering?


  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    I presume you are asking about a 2-stroke carburetor engine. When the fuel level drops to the bottom of the main fuel inlet, air bubbles get sucked into the fuel feed to the engine.

    The engine will buck and wheeze and eventually the rider will notice, but for a few moments the engine may simply run lean, not quite able to deliver all the fuel needed to keep the pistons cool. During that time, there may be a risk of engine damage.

  3. #3
    This is how I run a jetski shop in the desert nmpeter's Avatar
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    Quote Originally Posted by golferdude View Post
    Is it bad for the ski to run out of gas before switching to the reserve tank? I was just wondering?
    YES


    Four reasons:

    1-if the battery doesn't have enough reserve capacity to crank the engine long enough to reprime, you are screwed.
    2-Tigershark skis actually had a warning sticker indicating the possibility of engine damage if the engine was allowed to run out of fuel
    3-What K447 said
    4-"Only during times of war can we access the reserve "

    In simple terms...don't do it.

  4. #4
    Quote Originally Posted by K447 View Post
    I presume you are asking about a 2-stroke carburetor engine. When the fuel level drops to the bottom of the main fuel inlet, air bubbles get sucked into the fuel feed to the engine.

    The engine will buck and wheeze and eventually the rider will notice, but for a few moments the engine may simply run lean, not quite able to deliver all the fuel needed to keep the pistons cool. During that time, there may be a risk of engine damage.
    Yes you knew exactly wut i was thinking. So it would actually be better when your fuel lights get almost to the low side and before it would get to that point and start suckin bubbles to shut it off and switch it to the reserve line so theres no risk in running lean ever correct

  5. #5
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by golferdude View Post
    Quote Originally Posted by K447 View Post
    I presume you are asking about a 2-stroke carburetor engine. When the fuel level drops to the bottom of the main fuel inlet, air bubbles get sucked into the fuel feed to the engine.

    The engine will buck and wheeze and eventually the rider will notice, but for a few moments the engine may simply run lean, not quite able to deliver all the fuel needed to keep the pistons cool. During that time, there may be a risk of engine damage.
    Yes you knew exactly wut i was thinking. So it would actually be better when your fuel lights get almost to the low side and before it would get to that point and start suckin bubbles to shut it off and switch it to the reserve line so theres no risk in running lean ever correct
    You may not need to shut it down, but if there is some air in the Reserve fuel pickup it may stumble for a moment.

    Just back off the throttle to a medium/slow speed when you switch over, ride like that for a minute or so to work out any air bubbles, then start heading back to the fuel dock

    As Peter said, it is better to NOT need to switch to Reserve at all. Refuel before you get to the point of needing to switch to Reserve.

    Since the Reserve pickup is at the very bottom of the fuel tank, if there is dirt/contamination or water in the fuel tank, the reserve pickup will be the one more likely to suck it up. Using the main fuel pickup at all times reduces the possibility of something inside the tank causing fuel starvation.

  6. #6
    Quote Originally Posted by K447 View Post
    Quote Originally Posted by golferdude View Post
    Quote Originally Posted by K447 View Post
    I presume you are asking about a 2-stroke carburetor engine. When the fuel level drops to the bottom of the main fuel inlet, air bubbles get sucked into the fuel feed to the engine.

    The engine will buck and wheeze and eventually the rider will notice, but for a few moments the engine may simply run lean, not quite able to deliver all the fuel needed to keep the pistons cool. During that time, there may be a risk of engine damage.
    Yes you knew exactly wut i was thinking. So it would actually be better when your fuel lights get almost to the low side and before it would get to that point and start suckin bubbles to shut it off and switch it to the reserve line so theres no risk in running lean ever correct
    You may not need to shut it down, but if there is some air in the Reserve fuel pickup it may stumble for a moment.

    Just back off the throttle to a medium/slow speed when you switch over, ride like that for a minute or so to work out any air bubbles, then start heading back to the fuel dock

    As Peter said, it is better to NOT need to switch to Reserve at all. Refuel before you get to the point of needing to switch to Reserve.

    Since the Reserve pickup is at the very bottom of the fuel tank, if there is dirt/contamination or water in the fuel tank, the reserve pickup will be the one more likely to suck it up. Using the main fuel pickup at all times reduces the possibility of something inside the tank causing fuel starvation.
    Thank you this was exactly what I was looking for. I have a small tank 9 gallons so filling up early is obviously not an option so ill take my chances on the reserve line i guess

  7. #7
    Connecticut CrazyA's Avatar
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    What's Harry say ?

    Just throwing it out there. He's talking specifically about seizures. I remember reading this years ago and it seems to make sense. He's been building and testing well over 20 yrs.

    Seizure by running out of gas -

    as many people already know, a larger size needle and seat must often be installed into a carburetor to contend with the increased fuel demands of a moderately modified engine. If a modified engine is operated at full throttle with a stock size needle and seat, it will usually carry full rpm for about 2 or 3 seconds and then shut off as if someone hit the kill button. When the machine comes to a stop, the rider touches the start button to see what the problem is. The engine, no longer in fuel deficit caused by the undersized needle and seat, unexpectedly starts right up.

    This instant high speed shut off is caused by the carburetor literally running out of gas. It is sometimes implied that during this shut down moment of fuel starvation, the engine is also starved of the oil that is pre mixed in. This perceived oil starvation is then blamed for any subsequent piston scoring or seizure. Watercraft pistons do not seize in this way...ever.

    At the moment that the fuel starved engine shuts down, combustion and all the heat associated with it "ceases". Unlike a motorcycle whose rear wheel traction continues to move the pistons in the bores at a very high "friction causing" speed, the propeller and pistons in a fuel starved watercraft stop turning almost instantly. The heat and movement friction that can cause seizure are virtually non existent in a fuel starved watercraft shut down. This same concept applies to any machine that simply runs it's main tank dry before having to switch to reserve.

    It is possible for a rider, whose carb has an under sized needle and seat, to induce a piston seizure. However this would require a great deal of combined skill and stupidity. Once the rider has established that extended full throttle operation causes his engine to quit, he might make the very poor choice of only applying enough high speed throttle to avoid starving the engine. When he does this, he will be capable of maintaining about 90% throttle which will hold the engine endlessly on the lean thresh hold of fuel starvation. As this rider eventually masters this throttle position, he will be able to maintain a very high rpm with the carb feeding a horrifically lean mixture. Ultimately his finesse will be rewarded by one of the most abrupt and destructive lean mixture seizures that his mechanic has ever seen.

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