Rustybux

My 85 Formula plus has that huge airbox which makes it hard to work on the carbs. I was looking at DennisKirk Catalog and they sell Air pod filters for the carbs. They dont mention re-jetting like they do with motorcycles. I wonder if I have to rejet the main jet? They say it let's in more cold air and less restriction.

thank you

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RedRider_AK

You may or may not have to rejet. It all depends on your specific situation. Right now, I'm running my Fuji 488 engine with no filters or airbox at all, just open carbs. But, it's 28 degrees, and the machine still starts with half choke and then you have to flip the choke off or it dies. As soon as the temps dip, I will install some filters and check my jetting.

Install your pods, do a plug chop or two, and then figure out if you need to rejet (instructions on plug chops are available on the Engine forum as a sticky).

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lrnnorth

So whats the difference between having open carbs or little foam thingys in front of that. It shouldnt be any different jetting between those two. I would imagine you would have to rejet.

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RoadkillSTX

I would definitely rejet. Those snowmobile engineers know what they're doing. If you don't rejet you run the risk of running lean and blowing your motor. As well, the large airboxes act as a temperature and altitude compensator. With the little foam pods your sled will react differently to altitude and temperature changes. You might go out in the morning when its -10 and come back in the afternoon when its +3... your engine will either be running rich or lean on the way back if it was jetted for -10. (I can't remember if it runs leaner when its warmer or richer)
It's a bit of a controversial subject I suppose.

This is in the sticky "HOW-TO links" on the engine/driveline page:
Snowtech Magazine - Snowmobiles, Snowmobiling, Snowmobile Techncial Data

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SkiDooFormulaMX

put them on and do a couple wide open/warm runs with new plugs, then check the color, and if needed rejet accordingly.

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