Fuel?? Try a set of new plugs, I have had brand new plugs that won't work under compression.
Plugs wet when you pull them out? if not, try a bit of gas in the plug holes to see if it fires
If the plugs are wet, your motor might be full of gas (it happens) If they are wet, pull the plugs out, tip the sled on it's side (recoil side and pull it over. That will shoot gas out the plug holes (best done outside and protect the hood/windshield) Make sure the muffler is not full of gas too. Hate to have it go BOOM!!!
Oh yeah... crank seals???
