Hopfully I didnt just ruin my summer...

[Air Biscuit]

So this past winter I put a B pipe, msd enhancer, head, and air filters on the SJ. Today I rolled it outta the garage and started it for the 1st time. It was running fine on the hose, occasionally blipping the throttle. All of a sudden after a blip the thing never came back down in rpm and reved to the moon. In a panic Im hitting the stop switch, pulled out the lanyard, ripped the plug boots off it its still screaming. Finally after about 20 sec it dies. I'm hoping it was the enhancer the killed it due to the overheat sensor. I checked and it cranked over after that episode so I know I'm not seized. I found it odd that when i pulled the lanyard it didn't die. I checked the throttle cable and carb linkages, they're fine, they weren't stuck. I'm kinda freaked out to try and start it again haha. Any ideas??

 

[keith t]

Its called dieselling - definately due to an air leak somewhere

 

[tightithrash]

yeah its one of the scariest things that can happen......

next time just prime the living out of it or cover the carbs with your hands (assuming you can) and you will kill the motor. pulling the plugs does nothing but give you a sweeeeeet shock.

 

[Air Biscuit]

I thought that too cuz I did have the carbs off...Im gunna look it over tonight.

 

[Air Biscuit]

yeah its one of the scariest things that can happen......

next time just prime the living out of it or cover the carbs with your hands (assuming you can) and you will kill the motor. pulling the plugs does nothing but give you a sweeeeeet shock.

Yea it was a spure of the moment panic kinda thing lol

 

[keith t]

if youve only disturbed the carbs - its probably the gasket leaking, but could equally be the crank seals if its been stood a while

 

[Air Biscuit]

Its only been sitting since Nov. Seeing as I had the carbs off its probably that. I know air leaks can cause issues like this but this thing was wide open. Scared the outta me lol

 

[5810]

prime and pull WOT throttle, usually it stops it. Its a scary moment when it happens.

 

[cosander]

old gas is usually the cause.

 

[Air Biscuit]

Had fresh sunoco 93 in the tank

 

[kraqus]

I am thinking you are lucky it happened in your driveway..........


Benny

 

[Air Biscuit]

I am thinking you are lucky it happened in your driveway..........


Benny

Absolutly, this thing woulda been a missle on the water.

 

[kevbo]

Most all engines will do that unless they are tuned very rich at idle/part throttle. I can make all my boats and bikes do it. Next time keep your head and give it full throttle for 2/3 seconds, then hit the stop button. It wont ever happen on the water.

 

[Air Biscuit]

Most all engines will do that unless they are tuned very rich at idle/part throttle. I can make all my boats and bikes do it. Next time keep your head and give it full throttle for 2/3 seconds, then hit the stop button. It wont ever happen on the water.

What do you mean most engine will do that? I haven't looked at the ski yet, are you saying I might not have an air leak? I'm very meticulous when I'm assembling/working on anyhing. I cant imagine I F'ed up the carb gasket but its always a possibility. I rejetted the carbs when I put all the other parts I mentioned above on. This was the 1st time I was firing the ski up so my mixture could be way out. I know tuning should be done in the water under a load but I was shooting to get an idea of how my low speed was on the stand. But the thing was running no more then 3 min before it reved up. Should I fatten up the low speed alittle and try again?

 

[D-Roc]

mine will do it if out of the water and have airbubbles in the air line, that is why i hand choke my ski until i see fuel dump in the intake. then i turn on the TL. it forces the fuel to the carbs to actually prime the fuel system. cold motors need more fuel so on the first startup of the day i prefer hand choke over primer bulb. hot engines with low fuel in the tank out of the water will do it too. use a little aviation high tack on your carb gaskets to ensure no air leaks. if you suspect your lean down low then fatten up the pilot jet or lower your pop off pressure a bit. low speed screw should be used to set a smooth idle but can be used to see if you are indeed lean or rich. it could be any of these things and like mentioned lots of ski do it out of the water, make sure your throttle cable isn't holding your butterflies open because that can make for a runaway ski on the water and a screamming motor out of it.

 

[DAG]

haha, yeah i had mine do this 2 years ago. In the driveway after a ride go to clear out the waterbox and it reved to hell and back. I forgot what finally stoped it in the rush of things but damn it was scary.

 

[Air Biscuit]

Ok thanks for all the feed back. Im going to mess with it tomorrow and see what happens...

 

[FlightPlanDan]

Too high compression + too low octane can also cause it without an airleak.

The fuel ignites by compression only, so it needs no spark. Therefore, your kill switch and spark plugs become useless in stopping the motor.
All you can do is flood it with fuel by the choke/primer or stopping the air to the carbs with your hand.

What's your compression? I'm at 185 and 93 octane is good for me.

 

[Air Biscuit]

Too high compression + too low octane can also cause it without an airleak.

The fuel ignites by compression only, so it needs no spark. Therefore, your kill switch and spark plugs become useless in stopping the motor.
All you can do is flood it with fuel by the choke/primer or stopping the air to the carbs with your hand.

What's your compression? I'm at 185 and 93 octane is good for me.

Its an older west coast head. After assembly I measured 180psi, and I had 93 in the tank

 

[D-Roc]

i know a guy that broke his new 5 mil stroker in this way on the virgin start.....haha now that is heart pumper.