Can any of you advise me on the proper main jet for my DS? I've replaced the stock muffler cap with one having a larger (1 13/16") outlet diameter, installed a K&N air filter, and plan on running w/o the air box cover. I'll be riding at an elevation of about 500ft., air temps around 60 F. I'd like to install an EGT guage and am looking for the recommended thermocouple placement (distance from the piston) and the recomended maximum exhaust gas temperature. My dealer is checking w/Bombadier, but I haven't gotten an answer yet. Thanks, BillB

 

Don't know for the DS, but usually you want them as close to the engine as possible. The further away, the less accurate.

 

Maybe in the 175-185 range. A word of caution. Bombardier uses a lean jet needle. An exhaust, K&N filter, and airbox lid off significantly increases the air/fuel ratio around 1/2 throttle to full. I am not convinced that the stock jet needle is rich enough for these mods. A jet kit may be needed. I'd raise the jet needle and check your plugs starting with a fresh set, to be sure you are getting an accurate reading. If after these mods you notice that the fan is running more than normal, you may be running to lean!

Also, I heard that Bombardier has changed the jetting for the 2001 model. You might want to ask your dealer what jets/needles have changed.

If you are looking for more instant throttle response, a flatside carb w/accelerator pump is not a bad idea, or even dual carbs for that matter.

One other thing, have you checked your carb spring length? Many of us have had to stretch it from 110mm to 135mm, and sometimes more than once, to minimize the drop in the HP curve(hesitation) at around 3500 RPM.

 

Thanks for the info Scooby. I too had the spring issue. Thanks to the posts here, I stretched the spring to 135mm and am pleased with the throttle response. On SkiDoo sleds with Rotax 580/617/670 engines, Ive used EGTs at the distance perscribed by the SkiDoo racing manual (6-8" from the piston) and jetted to a W.O.T. temperature in the upper 1100's F. Since the DS is a 4 stroke unlike the sled engines, I'm not sure what temperatures to shoot for. Any advise? BillB

 

I have no idea what the exhaust gas temperature should be. That is why I have a 4-wire heated oxygen sensor. The only issue with a 4-wire heated oxygen sensor is you really need to know the temperature of the sensor and the sensor's response vs. temperature to get a real accurate reading. It is one tool, a piece of the puzzle when jetting, not the whole picture.

 

Tonight I re-jetted the DS. I now am running a #190 main jet, a #35 Pilot Jet, jet needle in highest position, K&N filter w/airbox lid off, Pingry's exhaust tip w/little-to-none packing, but baffle is still being used. I haven't tested it fully, just took it for a quick parking lot cruise. Plugs are gray. Will have to see how it runs this weekend. I want the DS jetted for maximum power (Air/Fuel Ratio ~12to13, not 14.7!)