Fly wheel turns slow

[BigAl61]

Fly wheel turns slow unless you pull the 4 plugs then it runs fast. I jumped directly to starter n fly wheel turned very slow. I put one plug in n started to turn slow again. Put all 4 plugs on and barely turned. Jumper cables from truck ground to motor n positive to starter.

 

[jerryjerry05]

Welcome.
First thing: is the battery good(had to ask)?? Load test?
​The cables good?
The connections good?
The starter good? The brushes can get gummed up and not work right?
Then the compression?? If you have low comp on 1 or more cyl. it can cause the problem.
Do a comp test. Make sure you ground the plugs or you can blow the pack.
If all of these are good??? Remove the lower unit and see if it's locking up or the bearings moving slow??