Engine will not turn off!?

[McDog]

I sold a SN with a 61x/61x 701 to a coworker this winter. He has been running it on a hose(I don't know why) and says that it starts building RPM's by itself after idleing for a few minutes. Then when he hits the stop button to turn it off, it will not turn off. He says he has to turn the gas off to get the motor to stop.

I have never heard of this before. The ski ran fine before I sold it to him.

He is looking to me for answers. Any ideas?

 

[oxnard111]

Sounds like the engine is dieseling. That is when the spark plugs become so hot that they continue to ignite the gasoline even with out spark.

For some reason the ski running too lean.

 

[wydopen]

air leak probably..

 

[tipafew]

I had this on a Sea Doo one time. I was winterizing it and decided to run the gas out of the carbs by shutting off the fuel selector. The thing screamed.
Looking back....that was stupid.
I agree, it could be an air leak causing RPM to build. Shutting off the gas could actually make a lean motor run even leaner and make the problem worse.
Next time tell him to pull the throttle wide open....That usually works better.
Time to check for air leaks though.

 

[McDog]

How do I check for an air leak? I did pull the motor apart and check it out brfore I sold it to him. I put new gaskets in it, but I didn't use any sealant because Clymer's didn't say anything about it. Should I have? I ran it for an hour or so right before I sold it to him with no problems. Could it be "deiseling" because he is running it on a hose too much/long, not because of an air leak?

 

[oxnard111]

How do I check for an air leak? I did pull the motor apart and check it out brfore I sold it to him. I put new gaskets in it, but I didn't use any sealant because Clymer's didn't say anything about it. Should I have? I ran it for an hour or so right before I sold it to him with no problems. Could it be "deiseling" because he is running it on a hose too much/long, not because of an air leak?

running it on the hose should not cause that problem...

there could also be fuel leak rather than an air leak. or even an obstruction in the fuel line. Or the fuel peacock could be clogged.

 

[Mark44]

I had a new motor run away, that is scary ******** right there!

Mark44

 

[oxnard111]

that is some scary stuff. I either pull the throttle all the way open or block off air flow to the intake.

 

[McDog]

I just talked to the guy again. He says he is running it on the hose for like 5-10 minutes. That seems like a long time to me, especially if the hose is not turned up enough.


And yeah, that would be some scary ****! I gotta help him figure this out before he rides it.

 

[oxnard111]

I just talked to the guy again. He says he is running it on the hose for like 5-10 minutes. That seems like a long time to me, especially if the hose is not turned up enough.


And yeah, that would be some scary ****! I gotta help him figure this out before he rides it.

the hose barely needs to be on when you run a ski on the hose. The engine temp on the hose is way cooler than true running conditions. Engine temp will not cause dieseling that I know of. The lack of fuel or excess of air will cause dieseling.

 

[McDog]

the hose barely needs to be on when you run a ski on the hose. The engine temp on the hose is way cooler than true running conditions. Engine temp will not cause dieseling that I know of. The lack of fuel or excess of air will cause dieseling.

Well crap! I guess this means I'm not finished wrenching on that ****ing ski after all. I should have just parted it out after I stole the b-pipe.

Can someone hook me up with some good how-to on doing an air leak test?

 

[oxnard111]

Well crap! I guess this means I'm not finished wrenching on that ****ing ski after all. I should have just parted it out after I stole the b-pipe.

Can someone hook me up with some good how to on doing an air leak test?

i couldn't tell you. when i had a dieseling problem it ended up being that my fuel line had a hole in it.

 

[McDog]

i couldn't tell you. when i had a dieseling problem it ended up being that my fuel line had a hole in it.

He did say that there was a lot of air in his fuel lines, but he also said the tank didn't have much gas in it. Could running out of gas in the tank cause it too?

 

[oxnard111]

He did say that there was a lot of air in his fuel lines, but he also said the tank didn't have much gas in it. Could running out of gas in the tank cause it too?

if it was right on the verge of running out of gas it might do that. but once the fuel level went bellow the fuel pickup tube, the engine should shut down completely.

but a little bit of air bubbles in the line is kinda normal, but if there are a lot of air bubbles, then it might just be a leaking fuel line.

 

[hangtime]

How about a bad stop switch .He didn't say it was revving all the way to the top of the rev limiter did he .

Have him pull the tether out and see if it shuts off .

If it was deiseling you would know it for sure because it will rev to the limiter and stay there .

You shouldnt run it on the hose for more than a few minutes anyways because your pump bearings have no cooling .

 

[yigaljet]

hello
first ,you should use "driebond" seal agent between crank case .
scond ,check the throttle cable for movment during bar turns .
third ,i would check fuel pickups in the tank ,for missing tubes
if you have a primer ,it could pull air from there
to check air laek fast , turn the engine on ,let it idle, when the idle go's up
use carb cleaner spray,and very cerfully spray it on crank case , and lower part of the cylinder,the second the engine idle nice again ,mark that spot theres your leak
if the angine dieseling spray into the carb ,or pump the primer it will shut the engine down

 

[oxnard111]

How about a bad stop switch .He didn't say it was revving all the way to the top of the rev limiter did he .

Have him pull the tether out and see if it shuts off .

If it was deiseling you would know it for sure because it will rev to the limiter and stay there .

You shouldnt run it on the hose for more than a few minutes anyways because your pump bearings have no cooling .

the ski will not bump off the rev limiter if a hot plug is causing it to fire from my understanding. Rev limiters cut out spark which there is no spark when the engine diesels.

I have never heard about worrying about the pump bearings needing to be cooled. They are sealed just like the midshaft, and the midshaft never gets cooled.

 

[tipafew]

if the angine dieseling spray into the carb ,or pump the primer it will shut the engine down[/QUOTE]

Pumping the primer to stop dieseling is a good suggestion.
His carb cleaner suggestion is good also.

Beyond that, a leak down test is really the next step in chasing air leaks. Before you go there, make sure the fuel supply is good. Throw another gallon in that tank for good measure. Like I said before....when it happened to me, the boat was on a trailer and running out of gas(shut off fuel).

 

[hangtime]

I think it is just a bad switch .
He didn't say it was revving out of control he just said it won't shut off .

 

[oxnard111]

I think it is just a bad switch .
He didn't say it was revving out of control he just said it won't shut off .

as stated in the first post

"I sold a SN with a 61x/61x 701 to a coworker this winter. He has been running it on a hose(I don't know why) and says that it starts building RPM's by itself after idleing for a few minutes."

he didn't say rev out of control, but does say it is building RPM's