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Just last week me and my dad went up to michigan for some snowmobiling becase theres no snow here in wisconsin. And we were on a straight so I gunned the throttle after a stop sign. The engine was not cold because i have just put about 50 miles or so previous to this incident. Well I have a roller clutch on my 440 and it don't engage till maybe about 6000RPM from a complete stop and about 5500 from a rolling start. I was going around 105 full throttle when I let go of my throttle. I didn't let go all the way but maybe to about 1/4 throttle. It started bogging down then i let it idle and it sounded like it was running it on 1 cylender. Well I took a look at it and it turns out I was. We got back to our hotel slowly but we still got there. We took the engine apart and noticed a burn mark on the top of the piston. We later removed the piston only to find out that I had blown a 1/4inch whole down the side of my piston. And I was wondering if because of the roller clutch it over revved causing my piston to blow. Oh and by the way, when I let go of my throttle I was at about 10500-11000RPM. Any help would be greatly appreciated to make sure this does not happen agian on the race track!
This is my first time posting in this forum so bare with me if I did it wrong.
 

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Thats frickin fast for a 440! At that rpm it is hard to say what might have caused it. How far did you run at that speed? What plugs were you running? What was the temp and what were you jetted for? Last year I forgot that I had jetted the wifes sled for a warm weekend and two weeks later it was COLD!! I leaned WAY OUT. I made it about 12 miles and no more mag side piston!
 

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If you have your slow speed circuit on your carbs set lean when you go from WFO to idle but the motor is still spinning fast you'll be running a really lean mixture...I'd guess the combo of spinning that motor way too fast (likely improper clutch spring or weights) and a lean mixture created the melt down you had. What sled do you have anyways?
 

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11,000 rpm's, good god that is way to high.. what kind of sled is it, with what mods....
 

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yeah i'd have a look at my secondary spring ,, i mean don't forget that if you lower your RPM , you might not get as much top end ,, but 11,000 is WAY to high man ,, you'll overheat in no time.
YOu should have 4 or 5 holes on your secondary ,,, your spring is probably torqued out to it's max , meaning it's in the last hole ,#5 ,, bring it down 2 holes to #3 and see what happens ,, this should lower your RPM,s
 

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it is important to know that prolonged running at WOT causes a lean condition. vary the throtle ,dont stay in the same position for more than 3 muinets at a time. lean=hot=burned piston especialy on 440s.
it may be worth your while to get a pyro guage.
 
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