Snowmobile Repair: 99 Arctic Cat ZR 700 Flat Spot, arctic cat zr 700, pilot jet

Question
My brothers sled is 99 zr 700 Cat and it has a bad,bad flat spot in the thottle at the bottom. Meaning that after wide open throttle,you can let the throttle all the way closed and when you go to get back on it, it has a very bad flat spot. If you don't let off the wide open throttle, you can kill the motor. But if you let off the gas again it will usually go again. Have checked the plugs-they are great, have cleaned the carbs three times thinking we missed a speck of dirt somewhere. Is this a characteristic of a large twin or is there something we can do? It is a reed induction. Our altitude is app.1120 ab. s.l.. The main jet is a 310, the mid jet is a 135, and the pilot jet is a 40, and the needles are in the middle notch. Any help or advice would be greatly appreciated. Thank you for taking the time to read my question. DA

Answer
Hello Dusty,

  Sorry for the delay in my response. It's definitely a fuel system related problem. All of the jets you are using in the sled are OEM except the MAIN. In the original set up, the sled would have a 290. My recommendation would be to install the 290 MAIN jet. One way to figure this out is an old trick. Take the clip on the needles and move them up a notch. If you notice better performance, move the clips back to where you had it ( middle ) and install the 290. If it doesn't change, or acts worse, try this. Move the clip one notch down on the needles. If this helps ( take it for a good spin ), then use a 320 jet. The latter will doubtfully happen. Something else to check, would be that the rubber carb boots/flanges that connect the carbs to the engine are not cracked or leaking. Spraying carb cleaner on them, and then going for a ride is one way to tell. Other than that, check to make sure the plugs are good, the big Cats eat them pretty quick. Hope this helps. let me know how it goes, or if you need any help. Good luck with the Cat! --Arcticatman