Running a Seadoo Out of Gas

[brownie545]

Hey guys,

Would running the engine out of gas ruin the pistons? My engine was flooding everytime I stopped the boat so I thought it would be smart to turn the fuel selector to off and run the gas out of the line when stopping the boat (apparently not smart). Then of course the boat wouldnt start. Got it back home and took the head off and noticed the top of the pistons were ruined and the rings blew out. I had checked the top of the pistons after the previous boat ride and they were perfect so this all happened in an hour period this weekend. Obviously time for a total rebuild... again, I just want to prevent this from happening in the future.

Thanks.

 

[Raven888]

As the engine runs out of fuel it begins to run leaner and leaner which means hotter also. It could burn out the pistons. It happened on an old dirt bike of mine that I rebuilt and re-jetted too lean. I burnt a hole through the piston.

 

[chipskittles]

I think maybe the motor was on its last legs already if running it out of gas burned the piston up. Anything is possible but part of winterizing/storing any motor is clearing the carburetor of fuel. Every time I put our boat away I shut off the fuel and the water and run it out. How else do you drain the carbs?

 

[brownie545]

I ran it out of gas a few times in a short period. So im assuming the pistons just got too hot.

 

[mikidymac]

It isn't very likely, read below from Group K....
"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."

 

[brownie545]

Well im sure I fall into the stupidity category. I tried to run it out of gas a bunch of times in a very short period. A couple times it ran for around 30 seconds before it died at full throttle.

Either way... time for a fresh rebuild.