I have a Panther 110PL-2B atv that I got for my son that won't start. I replaced the starter on it after running some tests and found that the old one wasn't any good and now the starter fires but drags really bad. If I remove the spark plug it will crank over perfectly but once I put the spark plug back in it it doesn't want to turn over at all. The starter, spark plug, and battery are brand new so those are ruled out I'm guessing. What would be other causes for this? I'm at a loss and any help would be appreciated.