Have riding lawn tractor with B&S engine model # JBSXS 5402vl. Full charged battery and new starter. So when it cranks over it stops spinning when it gets to compression stroke. Sometimes it will fire up before it stops spinning and it will run great. Any help would be appreciated. when I remove the spark plug it spins the the engine with no problem. I have to keep spinning the flywheel back by hand. What could be the problem? Thanks, Dave.