If you've dropped a cylinder, check for a dropped cylinder by starting the engine with earmuffs hooked up to the lower drive providing water for cooling and with it runnign pull and replace each plug wire one by one... each one you pull should result in a drop in RPM and the engine starts to kick a bit. If you pull one and there is no change at all... that is probably the dead cylinder. If you think you found a dead cylinder... shut it down, and then stick a nail or a bolt or something metalic up into that plug wire, hold it with something non-conductive such as a wooden clothesline clip so you don't get a good jolt and then have some one fire it up. Hold the nail closer and closer to the engine block... you should see a spark jump from the nail/bolt to the block around 1/4 inch. If no spark, that's your problem. If you see a spark, could be a clogged carb or a bad plug related to that cylinder.