a check I have heard on the 2 stroke jetskis to check for air leaks that are not directly next to the air intake is a can of starter fluid. spraying it (say from the opposite side of the sled) down on the carb boots or the crank seals will cause the engine to rev up if it is pulling that starter fluid in where it is getting air. I've never used this method on a snowmobile though.
be VERY cautious of this lean condition... although it may feel fine while riding it, lean is MEAN, it causes heat and I have seen a tiny airleak sieze a jetski engine.
oh btw I just last week replaced my carb boots on my 04 (I could stick my finger through them) and I found some on dennis kirk for $21 a piece. they are pretty much a stock copy that will eventually fail the same as the stock ones. the better option is the boyesen rage cage which uses a rubber hose with 2 clamps rather than rubber glued to aluminum. it comes with all new reeds and runs about $291.
stock boots ran about $80 a piece just for boots.