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Discussion Starter · #1 ·
Hey guys. Fall of 2015 I picked up a 1997 mxz 440 fan. Performed some minor tlc (replaced belt, spark plugs, fixed choke, etc.) Put about 300 km on it. Ran great, thought it had plenty of zip for a little 440 and would even pull the skis off the ground! So I unloaded it last week. Started it up to go for a ride, let it warm up. Idled great. Revved it up and the engine started to runaway. Sled started to take off so hammered the kill switch. Fired it up again and it instantly took off. I replaced the carb boots between the carb and intake. Tried it again and its still running away. I think I'm getting some extra air somewhere. Anybody have an idea of what could be wrong? Would be greatly appreciated.
 

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Could be starving for fuel ? Or leaky crank seals ?

Sent from my HTC One S
 

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Discussion Starter · #3 ·
I'm hoping it's not crank seals. Also I noticed I have a leaking exhaust manifold gasket. It looks like oil is dripping down from there. Would that contribute to this runaway condition?
 

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The leaking exhaust gasket is very common from the heat/cool cycle. You could try putting a turn on the bolts and snug them up. The run away at idle sounds like either a crank seal failed catistropically or you have something that is holding the carbs open. It is possible that the cable housing may have become snagged or the cable end moved in the throttle block on the handlebar and preventing the carbs from closing. You should be able to see the end of the cable housing poking out from the end of the throttle block with a c clip retaining it and there should be a little bit of free movement where the thumb lever moves before the cable takes up.
 

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I wouldn't be afraid of doing crank seals in it. its a fanner I could pull it out, flip it over, replace them, and have that back in the sled and running in a little over an hour. I had to do it to my 670 liquid when it back fired and knocked out my brand new crank seal.
 
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