Numerous threads for why my sled wont run when its warm, burned my sled down,look at these pistons, etc. maybe a common sense approach explanation can take some guess workout of jetting your sled,and why you need to change those settings due to certain conditions. The thing is you see all these people who say "put a bigger mainjet in it", its too lean from not enough wash on the piston, but whats not explained is that unless the person burned the sled down in a certain distance at a certain throttle opening you cant simply have a answer of a bigger main jet because thats false. You need to run a sled wide open for a distance of 750-1000ft to be soley on the mainjet,because all carb circuits overlap.To put this in perspective a 1/4 mile is 1320 feet long!
The reason for most of these burndowns and problems arise from the midrange jetting being too lean,and too low of octane fuel. By richeng up the needle your working the area of the fuel curve where your spending 80-90% of your time if your trail riding, not on the mainjet!
lets give an example of typical trail riding: your riding along a groomed trail averaging 50-60mph, you hit a large straight away, you whack the throttle,the sled speedo hits 80-90 mph,straight is a good 700ft long, here comes a turn,you let off the gas,dive deep into the turn and give it the gas again coming out and getting back up to 80-90mph. Then you come to a field opening after a small turn, on and off the gas,you rip it across the field to the other side to enter the woods again,for a easy 600-800ft again,back into the woods,turn by turn your on and off the gas.
The thing is,in this example scenario,you were never on the mainjet, you were on a combo of the pilot jet and the needle,needle circuit and sometimes getting into the needle/mainjet overlap if the straight distance was 750+ feet long for a short blip.
The needle overlaps with the pilot circuit(lowspeed) and the mainjet(topspeed) circuits. The needle controls how much of the mainjet will be richning up the topend circuit,because of your needle is still down in the nozzle,no mainjet increase is going to save the engine because its being restricted by the needle not coming far enough up out of the nozzle to flow the extra fuel desired. If your lake racing,across vast distances, again, the needle is in play ,because the very instant you let off the gas from a wide open run, your shutting off the main jet, and a lean needle will instantly burndown a engine on decelaration, this is actually what happens alot of times. People will again,put bigger mainjets in and they are working on the wrong part of the fuel curve.
Every sled made yamaha,polaris,arcticcat,evinrude(lol), whatever comes richer then needed from the factory,even a 2000 srx using 146.3 mains. The service bulletin was made for riders running very cold climates to go up to the richer yet 148.8/150 mains if the sled was going to be run for extended wide open periods. The reason they went back to the 00 jetting in 02 was simply the add on of dcs was to take the risk away and cover the wide open running situations. However the leaner jetting also provides more performance.
Simply upping the octane makes the sled richer without ever touching jetting!! The more octane you have the cooler the burn,so keep this in mind as you buy fuel,going cheap on gas fill ups provides less protection with a given set of jets,just simply from the octane level. octane level seems to have come into play alot more in the last couple seasons, 2 stroke sleds are most affected by the lower quality fuels. You need to richen the sled but richen the sled thru the circuit where your spending alot of the time riding the sled, mainjets are not a coverall like some people here like to say, they surely wont protect your piped viper running at 7500-8000 rpm doing 60mph down a trail, its the needle circuit you need to pay attention to. Also, when dealing with a viper,they have leaner needles and nozzles then a srx does,so take that into account when setting up your sled.