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Discussion Starter · #1 ·
Has this happened to anyone....input would be appreciated.....Running down the lake about 80 hit the gas hard for about 15 seconds and she slows down...I let go off the gas..hit the kill..come to a stop.....tried to move the clutch by had, it seemed stuck then freed up. Started it but missed bad so I shut it off. Took the centre plug out...aluminum colour....pulled the head.. piston melted at exhaust side and torched slightly in centre. Pulled the other heads everything fine, tan colour pistons, plugs dark. That day it was -2 C, used Sunoco ultra 94 first time do to gas shortage...earlier in the day the oil light came on and then went out but it was 3/4 full. When I opened the tank there was vacum. 2000, mild port job, timing key, cpr pipes running 390 jets. Any help would be appreciated. Thanks in advance.
 

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I think you ran it out of oil. I don't think there is suppose to be a vacuum on the oil reserve cap when you take it off. I think the caps are vented so it can empty without a "vapor lock" so to speak on the oil tank. Might have been as simple as a bad cap on the oil tank that wouldn't vent and went dry for a while in there. Good luck.
 

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Discussion Starter · #5 ·
Thanks, I will look into this further....I might pull the motor apart to check crank bearings. Could too much timing do this also? What about water in fuel?
 

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judging from your location can i assume the gas in your area is loaded with anti freeze and alchohol in the winter?????? both bad for a two stroke, alchohol in the gas will lean you out real quick, so when you hear people telling you to put dry gas and stuff like that in your tank, keep this in mind, on most stock sleds this wont cause a problem because they are jetted fat from the get go , but if you have had and re-jetting done and are riding the edge of a meltdown to start with, a simple switch from one fuel to a fuel with ethanol can do it.

if you have the ability post a picture, if the meltdown starts in the middle and gets wider and deeper towards the exhaust almost like a v shape i would say you simply leaned it out, those kinds of meltdowns are usually from beeing fuel starved or victimized by ethanol wich some fuel companies tend to go over the allowed amount they can put in the gas also.
shortage of oil usually cause overheats and side wall seizures first.
a timing meltdown usually produces a nice round shape hole right through the top of the piston.

the sunoco ultra 94 has a bunch of additives in it for cleaning also, i have on several occasions ran it, but i do have to watch my egt's when i have it wide open.
i run my sled at 1225-1230 but if i put the 94 in it'l climb to 1275 im using a digitron guage with the stinger sensors this seems to be the most accurate guage out there, at 1300-1325 itl melt right down
tip for anyone else that rides the edge on the egt guages, if you are wide open at max rpms and totally let off the gas you basically shut the fuel off swide open and it will actually melt after you let off the throttle, if your riding the 1250-1275 area i would back off slowly just a little bit , let it rev down a bit then let go.

just my 2 cents
dan
 

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Discussion Starter · #7 ·
Just back from a hot holiday...thanks for the info..I will post pick of piston..it is a lean condition as you have stated from the fuel.
thanks
 

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<div class='quotetop'>QUOTE (slick @ Feb 27 2007, 10:54 PM) <{POST_SNAPBACK}></div>
Most of the oil tanks have a vent line.[/b]
2001's (I believe) weren't vented and relied on the cap itself, friend had a 2000 ZR6 EFI do the same (collapse oil tank) when their caps became accidently swapped, starved it of oil also


<div class='quotetop'>QUOTE (racecar @ Mar 19 2007, 11:59 PM) <{POST_SNAPBACK}></div>
Just back from a hot holiday...thanks for the info..I will post pick of piston..it is a lean condition as you have stated from the fuel.
thanks[/b]
sounds lean, but, could still have something to do with oil supply as well, pop in some pics, let us see
 

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My thoughts would be that if it is from the fuel it is not because of the brand and grade, but rather from water contamination that lead to ice in the carb and blocked a jet passage. Any other form of crud in the carb could also block a jet passage and lean it out. The descripton of the melted edge of the piston at he exhaust port is a classic lean burndown. In general terms 94 octane fuel should make the engine run cooler than lower octane fuel. Another potential cause is an air leak, and most likely at the rubber carb flange, under the clamp. I don't think that a lack of lubrication would melt one piston like that. Look for other cylinder damage and damage to the other cylinders if it really was oil related.
 

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<div class='quotetop'>QUOTE (94ZR580 @ Mar 21 2007, 01:17 PM) <{POST_SNAPBACK}></div>
I don't think that a lack of lubrication would melt one piston like that. Look for other cylinder damage and damage to the other cylinders if it really was oil related.[/b]
unless the oil line itself somehow came off,, possibly air and oil, no?

Friends i'd mentioned had classic lean burndown appearance also I dunno
 

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You are running too LEAN on the main jets. This is where the problem occurred, at full throttle and the precise time where the main jets are really functioning @ 100%. Considering the porting and the timing key along with the fuel additives, there is no reason why you are not running atleast a 420 main jet or larger.
Timing keys LOVE higher octanes and fuel in large doses!
Piston wash should tell the true story, post the pics of all 3 piston tops and go from there. A picture is worth a thousand words!
Egt's are a great tool, but if your oil mixture isn't set correctly they're not gonna do alot for ya.
 
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