Can anyone solve this mystery?

[Johnny340]

I have a PJS VHP (Kawi 550 Reed motor) and after riding yesterday, I loaded it on the trailer and fired it up to blow the water out of the pipe for a few seconds. Well, with the throttle at idle (everything is working perfect here) the thing revved up to 9 million RPM and the red kill button did nothing!!! I shut the fuel off and it died before I could get the hood off to pull the plug wires. (5-6 seconds)
So how was it getting both fuel and ignition? Throttle closed, ignition stop button pushed (which also functioned correctly all day.)

 

[WFO Speedracer]

I have a PJS VHP (Kawi 550 Reed motor) and after riding yesterday, I loaded it on the trailer and fired it up to blow the water out of the pipe for a few seconds. Well, with the throttle at idle (everything is working perfect here) the thing revved up to 9 million RPM and the red kill button did nothing!!! I shut the fuel off and it died before I could get the hood off to pull the plug wires. (5-6 seconds)
So how was it getting both fuel and ignition? Throttle closed, ignition stop button pushed (which also functioned correctly all day.)

Thats no mystery its called closed throttle runaway and is usually caused nby an air leak or extremely lean fuel condition..

 

[Johnny340]

Would simply shutting the fuel off be enough to cause this as the fuel ran out and leaned out?

On the air leak thought...I flooded my engine with water earlier in the day somehow. I assumed water went in the intake but the filter seemed dry. If I had a case leak would water get sucked in there?

 

[WFO Speedracer]

Would simply shutting the fuel off be enough to cause this as the fuel ran out and leaned out?

On the air leak thought...I flooded my engine with water earlier in the day somehow. I assumed water went in the intake but the filter seemed dry. If I had a case leak would water get sucked in there?

doubtful:icon16:

 

[Johnny340]

Doubtful that running out of fuel would lean it out to the point of closed throttle runaway or doubtful that water can be sucked into a case air leak?

I presume the best way to check for air leaks is by buying a kit of some sort that plugs intake and exhaust, etc and allows you to pressurize??
Thanks.

 

[WFO Speedracer]

Doubtfull on both accounts actually

 

[DAG]

Next time it happens, this might sound crazy, but pull the throddle WOT, and keep pressing the stop. it will kill out in 2-3 seconds.

 

[DAG]

watcon has a leakdown test kit i believe. or you can make your own out of the rubber tube inside a go-ped tire or simmuler.

 

[SuperJETT]

Next time it happens, this might sound crazy, but pull the throddle WOT, and keep pressing the stop. it will kill out in 2-3 seconds.

Ditto, ditto, ditto, next time or any time you get a run-on, hit/hold the stop button and pull the throttle wide open to kill it.

 

[Johnny340]

Thanks for the advice for next time. (I still wonder what the ignition source is when this happens...something like detonation??)

This sounds fairly common. Is it something people just live with or should I fix it so I don't seize my engine one day by running too lean due to this air leak?

Anyway, the watcon kits looks good or like you say, maybe I can make one. If I make my own, what PSI should I pressurize to and what are normal leak down numbers?

 

[cosander]

Thanks for the advice for next time. (I still wonder what the ignition source is when this happens...something like detonation??)

This sounds fairly common. Is it something people just live with or should I fix it so I don't seize my engine one day by running too lean due to this air leak?

Anyway, the watcon kits looks good or like you say, maybe I can make one. If I make my own, what PSI should I pressurize to and what are normal leak down numbers?

http://en.wikipedia.org/wiki/Dieseling

 

[hmsikhayn]

yes it could you start to lean out just as the gas empties out from the carb happens to my bikes (2 stroke) all the time but i would still do a leak dowwn to be safe

 

[Johnny340]

That site on dieseling was good info. I'm wondering if this happens sometimes anyway for two strokes or does it always indicate a bigger problem (air leak).

If no one else can verify that this just happens occasionally to tight engines too, then I will have to do a leak test. I see the gauge in the kit goes to 15PSI so I presume something slightly less than that would be a good starting point. Ideally, I guess there would be no leaks at all but there must be some 'normal' tolerances. Does anybody know what there are?

 

[WFO Speedracer]

That site on dieseling was good info. I'm wondering if this happens sometimes anyway for two strokes or does it always indicate a bigger problem (air leak).

If no one else can verify that this just happens occasionally to tight engines too, then I will have to do a leak test. I see the gauge in the kit goes to 15PSI so I presume something slightly less than that would be a good starting point. Ideally, I guess there would be no leaks at all but there must be some 'normal' tolerances. Does anybody know what there are?

On that particular engine I would definatly do a leak test ,those seals have to be like 12-14 years old by now
:sadwavey:

 

[Johnny340]

Actually they are 'only' about 4 years old. The engine was rebuilt (new crank, etc) and then assembled, ran for 5 minutes and then put on display for 3-4 years. This past month is the first time its had any use. That's why I thought that it should be OK.

 

[Boris]

Before you run out an pull the motor apart looking for an air leak, check your spark plugs.

If you are running dangerously lean that can cause a run away as well.

 

[Johnny340]

Boris, funny you should ask about spark plugs. The day before I was riding and the engine was running well but then it totally crapped out and wouldn't rev up all of a sudden. I thought, because it's hardly broken in, that I may have seized it. But then it turned over fine so I changed the spark plugs and it ran like a top again. I didn't do a proper high RPM read on the new plugs but after the next couple hours of riding they are quite dark; like too rich.

What gap are you running on your BR8ES plugs?

 

[ATS_Aaron]

I had the same thing happen on a Kawi 650Sx. I pulled the motor twice to leak test it...in the end it turned out I was low on gas and it did in fact cause a run-away condition.

Aaron

 

[WFO Speedracer]

I had the same thing happen on a Kawi 650Sx. I pulled the motor twice to leak test it...in the end it turned out I was low on gas and it did in fact cause a run-away condition.

Aaron

That particular 550 engine he is running is very high strung and in a very high state of tune ,its not super high compression but I would be very wary of it if it did that ,it wouldn't take much to screw it up but good.:Banane09:

 

[dajnglst]

On the old 550's some guys used to put oil in the front engine cover, if the front crank seal goes bad and you have slight air leak it could use that oil as fuel for diesel action. I have had run aways with plug caps removed and rags over intake trying to kill engine to no avail.

Check low speed mixture screw o-rings, and if they are stuck in carb body, get a new carb.I was tryed to cheat it with xl 700 carbs and after doing leak down and new reeds and gaskets on intake, it would still do it.

I have even run into issue on sea doo 650 engine with leaking front crank seal. Boat runs normally until you get a 2-3 passenger load on it. Then there is only half power. The front crank seal spring is inside case. When it goes bad it, the spring gets sucked through engine. Because that case cover is sealed with starter and front cover it does not suck air in but allows primary compression to be bled off. Losing the mixture through the seal into stator cover. 720 engine awaits this boat, so I will just run it until it dies.

"You ever see seat grabs on an explorer?".