ProX 600 carb issue

[turboDS1300]

I am working on a Pro X 600 for a friend and am scratching my head about some symptoms it is exerting in the very low throttle positions (0-1/4 throttle). The sled starts great, has crisp midrange, and good topend, with good plugs and piston wash. The issue I'm having is the sled seems to drop a cylinder at about 1,400-1,600 rpms whether its cold or after its been running. The sled will come down from operating rpms and as soon as it hits the range above, it will make a fairly loud sputter and begin to die. As soon as it drops to 1 cylinder, the sled is obviously quite boggy and takes some throttle feathering to bring it back up to operating/engagement rpms. I've already tried to adjust the idle mixture screws for each carb on the TM38 rack and have thoroughly cleaned the carbs too (complete disassembly and cleaning). Anyone have any suggestions are baseline settings? I'm currently at 1-3/4 turns out on the mixture screw. This is a flatlander sled setup for Minnesota ditches. Any ideas?

 

[rocket]

Dropping cylinder

I am working on a Pro X 600 for a friend and am scratching my head about some symptoms it is exerting in the very low throttle positions (0-1/4 throttle). The sled starts great, has crisp midrange, and good topend, with good plugs and piston wash. The issue I'm having is the sled seems to drop a cylinder at about 1,400-1,600 rpms whether its cold or after its been running. The sled will come down from operating rpms and as soon as it hits the range above, it will make a fairly loud sputter and begin to die. As soon as it drops to 1 cylinder, the sled is obviously quite boggy and takes some throttle feathering to bring it back up to operating/engagement rpms. I've already tried to adjust the idle mixture screws for each carb on the TM38 rack and have thoroughly cleaned the carbs too (complete disassembly and cleaning). Anyone have any suggestions are baseline settings? I'm currently at 1-3/4 turns out on the mixture screw. This is a flatlander sled setup for Minnesota ditches. Any ideas?

Can you tell if the one cylinder is losing fuel, getting too much, losing spark or anything else? Is the cylinder you're dropping the on the same side as the fuel pump pulse line? Any sign the float bowl on either of the carbs is getting "flooded"? Has the sled been run in lots of snow and the problem appeared afterward? Any information you can offer will be helpful.

 

[turboDS1300]

I'm not in front of the sled right now and I don't remember what side of the crankcase the pulser line comes out to the pump so I can't provide insight to that question. The actual float ballasts in each bowl are sliding smoothly and are not stuck. I am not sure about the needle seat, but my issue (to me anyways) appears to be occuring in such a specific area that if a needle seat wasn't sitting tight I would be experiencing problems in a broader range of throttle positions than I currently am. This issue happens upon first starting the sled when its completely cold and also after its been fully warmed up. To answer your question, it did not start after running in "deep" Minnesota powder. Thanks for your reply Rocket.