Snug it down and try moving it CCW a little at a time. Dont move it more than a 1/16th of an inch at a time. It must be close if you say it has fired a few times. Sounds like it is a little retarded from your explaination.
A fresh set of plugs may help you. If you have been cranking it a lot the old plugs may be loaded up. I would not use either as it can do more harm than good.
Artificial Intelligence is no match for Natural Stupidity