If the compression is there, and it spins easily with plugs in I am not sure what else could cause that. One of the more experienced guys here may have another idea. But I guess the real question is does it run smooth and move smooth? If so then it may just be normal. I just know with out plugins in it the compression does not compress as the hole is open... Ill keep watching to see what others say.
I'm not really familiar with that particular engine, but I think 124 is kind of low for twins around then (130+ is optimal). Not to the point of needing a rebuild, but time to think about it over next summer or something..
You you might want to look at the reeds for being worn out as well.
But, if the sled runs well as it is, I wouldn't worry about it too much.
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