I get this call about once a week. Customer says they started the ski on the trailer, blipped the throttle and it started running really fast. Letting go of the throttle did nothing. Pulled the safety lanyard and it still didn’t quit. Pulled the spark plug wires and that doesn’t make it quit. Finally, they thought to pull the choke, and that killed it.
First, how could this happen?
This is an indication of a severe lean condition. Either the engine isn’t getting enough fuel (fuel pump issues, but more likely carb circuit clogs), or the engine is getting too much air (case leak, crank seal leak, intake/reed cage leak). When it gets above a certain rpm, it starts to come onto the powerband, making the lean condition worse. The spark plug quickly gets real hot, which will then ignite the fuel even if there is no spark.
What should I do if the engine runs away?
The easy answer is to shut it off, as quickly as possible. But, given that the engine might continue to run with no spark, shutting it off can be difficult. If the choke works well, that can sometimes kill it. If the airbox is off, a rag in the carb openings works real well. If you have a primer, you might be able to squirt enough to kill the motor.
What should I do to fix the issue?
Is it the carbs or is it a case leak, intake leak or crank seal issues? On some older models, cases and crank seals should be suspect. 20+ year old seals might not seal any more. But, the primary cause is usually carbs.
If you don’t know when the carbs were rebuilt last, that is step one. Fully clean and rebuild carbs. Rebuild simply means put them back together properly with all new components from a carb rebuild kit. If you don’t do carbs every day, use the genuine Mikuni kits as they work better, and are easier to get right the first time.
If it isn’t the carbs, check the crank seals, looking for any weeping oil around the seals which means they are done. Also, look for any other oil seeping out of the engine and check the gaskets and seal in the intake manifold and the carb to manifold gaskets. The cases can be resealed easily, and at the same time the crank seals can be replaced.
Is there more info?
I have seen every model 2S engine run away at least once. There are some that are more common victims, with the 951s seeming to do this more than other skis.
It is rare to have a ski run away in the water. A little bit of load on the engine will prevent the surge when you release the throttle, which is why this is mostly a problem seen on the trailer.
If you are on the trailer and running the hose, be sure to shut the hose off before you get the engine to stop running.
Don’t pull the spark plug wires. If they are sparking, you will get shocked and if they aren’t sparking, pulling them off won’t do anything.
