So it seems to work fine, and spins the engine without the plug installed. When you add compression to the equation by installing the glow plug - which greatly increases the difficulty of cranking as it should - it doesn't crank the engine very well. Some time ago it got hot and smoked.

2+2= the conclusion is that your starter setup is pooched. It is hard to get past that point because the info so far points squarely at that. Esp since you say it cranks fine by hand. But you have not tried to start it by hand. Why don't you try that and get back to us?

Once you apply a starter setup that can actually crank the engine, and you still have problems, then it might be possible to offer other suggestions beyond all the obvious overprime/hydraulic lock issues you should be eliminating already anyway. To be sure one last time, remove the plug, and the fuel/muffler lines to prevent any further fuel entering the engine. Crank it for 2-3 seconds plug out to make sure the crankcase is emptied of excess fuel. Install the plug, not the fuel lines, and try again. Same thing? One more step, try hand starting it.

If you can't hand start it at all, and the starter won't crank it, it is kind of tough to home in on a diagnosis because the information is little more than "it won't start".

Won't crank, but will hand start = get a better starter or starter battery.. and one thing that is often a culprit, make sure the d- battery connections are solid, some of those banana plug affairs are total garbage from the get-go. You need several amps tp flow through those connections soan iffy cheapo banana plug like so often comes with starters is trouble. Mine come off and get Stakons. I have a starter that claims it can turn over engines up to 20cc but is no better than my old Sullivan that is going on 15 years, and can barely crank over a .65 hooked up to a 7Ah gel cell.

Won't crank, and won't hand start = too many possibilities at this point.

MJD