I have a '78 model Johnson 70 hp. It has setp for about 2 years. The starter will engage the flywheel and the flywheel will turn a little bit, then stop. The starter gear stays engaged, but the starter shaft keeps spinning. I have to disengage the starter gear by hand and retry. I removed the plugs and sparayed some Marvel mystery oil inside. With the plugs removed, the flywheel turns easy, but with plugs in, there is much more resistance. need help. Thanks.