Alright, here's what I've got goin on. Before the season started I did a top end rebuild (99 MXZ 600) and cleaned both carbs. I'm having trouble getting the idle up to the 1600 rpms. that is recommended. I set the carbs to spec according to the cd that i have, which has the air screw only a half a turn out. So as it sits it idles low enough that the tach just bounces and won't read even with the idle screw turned all the way in. I don't think there is an issue with the tach because if I give it just the slightest amount of throttle I can get it run steady (and read steady on the tach) at 1600 rpms. I tried turning both air screws out another 1/4 turn and got it to idle at about 1000 rpms. Could there be something else causing it to idle so low? Obviously the idle screw shouldn't have to be turned all the way in, and I'd rather not keep turning the air screw out if spec is supposed to be at just a half a turn. The only engine mods are Vforce 3 reeds that were put in by the previous owner (this is my first season with the sled). After letting it run for awhile the plugs do seem a bit wet.

What about the fuel screws?

I have the air screw a half turn out if that's what you meant my fuel screw. How many turns out do you other 99 mxz 600 owners have yours set at?

It sounds like you may have a vacuum leak between the carbs and the engine block. A vacuum leak won't allow enough vacuum to pull fuel from the idle mixture cavity, therefore you would have to crank your idle screw in all the way to lift the slide high enough to allow fuel to pass through the main jet. If this is the case, I would check the seals or gaskets between the carbs, reeds, reed cage, and block for imperfections. If it were me, I would replace all of them.

I have had a similar problem as yours. My '98 MXZ670 does the samething and l found it interesting to hear about your problem. I would not go changing all sorts of parts and spending money unless you absolutely have to. Doing that is like fixing your car. You can't figure it out so change everything. Each to their own, but check each thing out first then decide what is best. Mine tends to not want to idel properly especially when it is warm. I went out yesturday and most of the time it was fine except for the odd time. I have noticed as you turn in your idle screw on either carb that it gets to a point when the idel will really increase and it is almost there is where you want it. Sometimes mine won't stay idling by itself especially when it is very warm out. I have guessed it is just one of those idiocykrycies of Ski Doo. I have no boot leaks or carb leaks. L have not fiddled with my air screws cause so far the engine has burn burning really well. I also know the rotory valve engine is different from the reed valves but the same principle applies. One possibility could be your reed valve flaps. Check the flaps to see the force of them closing and to see if you can see through them or not. I have been told by shop mechaincs that you rmight have to change those reeds around 4000miles give or take. Like anything else they wear out.

I had the same issue on my 2001 MXZ - X 800 this December...

1. Check the intake boots for cracks. They are between the air box & carb. Mine had a crack and was sucking in too much air. Replaced them & added v-force reed valves.
2. If the intake boot needs replaceing, change the plugs as the added air will cause the plugs to get residue.
3. Adjust the idle & gas valves... you need to adjust both, not just one or the other.

Now, my sled runs like a Farrari! Idles right at 1300 - 1600... perfect!

How can I tell if I have any vacuum leaks and what are the "idle and gas valves"?