I know this sounds stupid, but what exactly is piston wash, and how does your sled get it?

the fuel and air that comes into the jug goes across the top of the piston as it comes in . Gas is some what of a cleaning agent when it comes to carbon. Well if your running lean its really hot on the top of the piston and most of the gas evaporates as it enters the jug, this is why you have very little "wash " if your lean. The pipe does have some factor in this also but thats a whole differnt day at school.... If the motor is running rich more gas enter the jug as a luquid and cleans more the the top of the piston = more wash. Does this make sence? or did I go to fast explaining this wash deal...

that makes sence, but what color or how much wash is good?

tan spark plugs with 1/4 of the electrode clean. as for piston wash you should have (two) 1/4"x 3/16" spots of clean piston top on the intake side of the motor.If you have the head off the center of the piston will have a slightly shiny oily film and the outer edges will be dryer with carbon. if it doesnt have the oil shine in the center your to LEAN! If you ever look at a motor that burns down the back side of the piston dome is covered in lightly burnt oil film (carmel color).

how will it look if you're too rich?

the outer edge of the piston will be clean more then the 1/4 x 3/16" I have talked about. the richer it is the more of the pistons edge will be clean (mostly on the intake side) If its really lean like burn down lean you will have dry black carbon starting in the center of the piston and going across the top towards the exhaust port, and very little if any wash on the intake side. it is possible to have a little wash (very little) and be lean, you must read all the info your plugs and piston tops are giveing you! white plugs and your lean, coffee with cream your close,black to rich!

Now I am confused.... My sled is stock all the way through and anticipating the arrival of my SLP pipe yesterday (didnt come :banghead: ) I have the pipe, y-pipe, & silencer out of the sled. Being Curious George, I tucked my head down there to see the piston crowns. There is a big time caked-carbon party all over the crowns.... according to the above posts, carbon cake is burn down lean??? Could the cause of the carbon cake party perhaps be excessive idle time, extreme rich condition (choke on for a minute-two idling), ..?? Carbon cake party is my nickname for excessive carbon buildup... must have rode the short bus today.

---Now a dumb question.. I am understanding the piston wash theory.. cause/effect of lean & rich. To start from scratch and get a true reading of piston wash, I should take off the head & erradicate the carbon cake party first, right? Get a clean piston as a baseline.... clean with what? Light abrasive & carb cleaner OK or no..i.e. scotchbrite??

---Can I re-use head gasket..o-rings..?? Never had it apart, thats why I sound a bit clueless.

---With the head off..it sounds like a great time to head over to the machine shop and take 0.015" off her... How would that slight increase in compression ratio effect carbeuration (cant even spell it :frech32: ) :augen41: Would it be worth the effort??

Didnt mean to write a book fellas.... :beerchug:

There are much better pictures but I cant find them, at least this will give you an idea now how it should look.

http://eric-gorr.com/tech/pistonguide.html

You can clean the top of the piston with scotch bright with the piston all the way up in the bore, just get ALL the crap out from a round the top at the rings( compressed air) . the rubber orings are reuseable, dont clean them with solvents they tend to streach! if they streach put them in the freezer, they will get smaller.


Dont wack .015 off the stock head, it will effect the squish. the combustion chamber shape and size is what causes det , cutting the head will make it more sensitive to fuel quality! your slp pipe will not show much HP over stock unless your jetting is really close, hot pipe makes more power.... to get a hot pipe run it leaner, without det is the key!

Is there a good way to check for wash through the plug hole?

Yeah, buy a Benda-lite from Sears and stick it in the bore with the piston all the way down. You'd be suprised how much you can see.

I located these pictures, are a better view of what you sould be looking for. They are both on the rich side. Depending on the sled this is 1 or 2 jet sizes rich and still be well on the safe side.

http://www.snowest.com/fusetalk/attachment...istonwash%2EJPG

In my opinion those pictures are of a PIG rich motor, I like to see wash that is the size of a pensil wide and 1/4~3/8" long only at the intake ports!


Read this , this is the best information you will ever read!

http://www.snowtechmagazine.com/articles/2...ne/baseline.php

consider BUYING the skidoo carb tuning VIDEO(gerald karpick) and Aaen carb tuning manual. it goes into wash and also reading the ceramic part of spark plug in addition to the electrode. well worth the investment considering gas will be $3.00/gal next season. i got the wash baseline down and then used EGT with dial a jet. fun to do a click and watch the EGT react. tempraflow may be simpler. next year.

how does a dime sized wash sound?

every motor reacts slightly differnt to changes, if you have EGT temps get your wash close and tune your egt so the midrange is around 1080~1130 peak and your WOT for a long run is around 1150 peak! these numbers are safe, yes you can get leaner but for what you can gain in my opinion its not worth getting closer to the edge!

triples can run hotter. flame speed accross the dome is faster/shorter. especially a 600 triple.

Thats about where mine runs in the regular mode, dime size with shadows that carry back to exhaust this gives you a little freedom when running longer distance, fast and or in loose snow. Prem. mode, it tightens up a little more. A tweak on the Tflows when its a beer/soda run!!!!Short runs only..