What we've determined is a combination of several things. First off, they run rich, not lean. Too much fuel caused by a combination of things. First, the EFI temp sensor in your air box is reading intake air temps. The winter temps are obviously cold, that triggers the FI to add a bunch of fuel. The lower unit is in a snow bath all day and is covered in an ice burg. That cools your oil. Cold oil in your valve train and cylinder under your piston causes poor ring seal. With cold oil and poor ring seal, and the FI adding fuel running in a "cold mode", you get a ton of piston wash and end up with gas in your oil. And the final factor that compounds the problem, is stock air boxes eventually fill up with snow reducing air flow. And/or the air box is so tightly sealed with foam, the foam eventually compacts with snow and again, air flow is lost, compounding the "rich" over fueled condition.
The good news is this condition is nearly corrected with a couple simple mod's. #1- install the KTM 70 degree "C" thermostat to keep engine temps up, #2- Install a good intake system to keep an abundant supply of air to your engine, "off-sets" the rich condition and excess fuel, and #3- install an EFI tuner the Dobec Gen-4, or the "Bazzaz" self mapper and correct the cold temp/excess fuel condition to an AFR of ideally 12.8 to 13.0
I am currently working with Francois at Bazzaz in developing a simple "Snow-Bike Box", that will be a simple plug in and go box. No mapping or tuning required. As soon as we have sufficient snow, I will be mapping and collecting data on a test unit for the new box. It should be available later this season.
When riding, remember your "cold starts". Give your entire engine time to warm up completely, which includes your oil.
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