Snowmobile Repair: 1991 polaris indy 500 snowmobile, polaris indy 500, indy trail

Question
I have a 1991 indy trail deluxe 500 snowmobile. I got it out for the year and it runs great for say 5 to 10 min and after that when you slow down and let of the gas and try to go again it acts like its got a fouwled plug but then it will take off and run great while you are on the gas.
I took the carbs off and they are spotless and the fuel line if ok and the filter is also fine. the spark plugs are brand new.  i dont know what else to try. do you have any ideas

thanks bryan

Answer
You are probably fouling a plug at low rpms.  This a very typical Polaris problem.  As soon as you get the rpms up it will clear it self out.  Check you plug gap I believe it should be .025.  But check the book and make sure.  If the gap is too close there won't be enough spark to ignite the fule also if it too far the spark may not be strong enough to make the gap.  You may also have a weak coil.