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I was looking at the top of my pistons and they are nice tan over about 80%-90% of the surface area of the piston top, with the clean part around the edge of the piston. Does this seem right? If pistons have no tan on them is this too rich, and if fully tan is that too lean.

Does anybody know?
 

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There has been a lot of debate on this especially on snowest, but in general a perfectly clean piston means too rich and too much carbon means it is too lean. You should have a small amount of wash or clean area on the intake side of the piston.
 

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I believe it is the other way around Mesickzr. The piston on the left indicates that its too lean and should jet richer. There is less carbon on there because there is some detonation occuring...
 

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KungFu MeSick is right.
If the top is clean. that means it's to rich. The pistonm runs cool and the charge cleans off the piston top
As the charge leans out, the piston top heats up and cokes the oil onto the top.
If the piston top is completely coked up. You are running too lean, the piston top is hot and is cooking the oil to it!

In a perfect world you should have a dime size area that is clean just next to the intake port. (The cool charge keeps the piston coolest there.
 

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The chart is right
 

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Like I stated, there has been a lot of debate on this subject on snowest. I got the chart out of snowtech magazine.
 

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Strange, exact same chart is in back of perf manual. AC better sue, copyright infringement :p
 

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I'd have to agree, that chart looks right. My ZL was acting up so we took it to the dealer. They checked and the pistons were burned down, well atleast the corners anyway. Problem was it was leaned out(by bad gas, leaving a residue in the jets, hence leaning it out) and they were carboned up bad, and rounded on the outer side. Luckily it didnt score the cylinder wall, so all is well, i am just amazed that the sled still ran as good as it did considering the pistons it was only around 6500rpm that you could tell it was loosing compression. Guess a good cat never dies. :p

Lucky
 

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Originally posted by Luckyrider@Mar 12 2003, 08:15 PM
Guess a good cat never dies. :p

Lucky
Don't forget they have 9 lives :D
 

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the chart is right !!!
the top of the piston will usually have a black crown in the center and where the exhaust port is that will also be black . where there is a clean ring around the outside edges that is where the fuel comes into the cyl via the ports . the air fuel mixture cools the combustion chamber when it enters and thats why you will see the caramel colored outter ring , the richer the air fuel mixture the more "wash" you will see . the leaner the mixture the more black you will see, the black is carbon that sticks to the hottest part of the piston thats why the center is black and usually the exhaust port area. the ideal situation is having the outter ring a clean/caramel color with a black center just like the chart states. if the edges of the piston are erroded that that is a sign of to much compression or a timing issue , if the center of the piston is pitted that is usually a lean detonation issue .....its hard to pinpoint damagae untill it happens so follow the chart and check the "wash" from time to time, its more accurate than reading plugs because todays fuels are so whacky :wacko: with additives its very touch to get an accurate plug reading .speaking of plug reading , dont just take the plug out and look at it unless you go wot accross a lake and just shut the sled off, any other way will give you a false reading, even one second of a let off or blip off the throtle will chnage the color of the plugs..........
 
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