I also would try to tune the carb. A lot of times when a plug gets fouled from over fueling it is toasted and will not fire right, even after cleaning. I just went through this with my dakota engine swap. Buy a new set of plugs and try it again. Turn your carb screws out 2 and a half turns and see what it does. I also ride sled in the winter and motorcycle in the summer. When a plug gets fouled it goes straight to the garbage can. When I put the smallblock in the dakota I used an old set of plugs with a new carb and a different distributor. Had the dizzy in 180 off and fouled plugs. Even after getting it fired up I still had to put new plugs in. Just another example of plug problems is a co-worker sold his newer arctic-cat sled for very cheap because the mag side cyl would not run right. good comp and a great spark with the plug out. Plug in ran like crap. Sold it and the new owner put two new plugs in and it ran like a new sled. Old cleaned up plug would not fire under compression. Taught me a lesson also.