ok , so at least now the carb is eliminated from the cause . another points and condenser , a weak spark can blow out under pressure . with the amount of fuel that has been through it . by now you should see if its the bottom seal , did you check top one with a little fuel too,look for tiny bubbles . remove the cam when you do points it should be a reasonably tight fit but it does come off make sure they key is in correctly when refitting wink or it just stays still . the engine itself did seem strong