I have a Duromax 440 with that exact cover. No starter problem. The Duromax uses lots of the same parts as the 390. It's a clone like the Predator 420. I got rid of the counter balancer. I can't really tell the difference. I assume being you are looking at a billet side cover you have other mods as well. If you put in a Billet rod it'll hit the counter balancer. Make sure to remove the bearing on the flywheel side as without the balancer in it could possibly fall out which would be certain Armageddon of the high degree
I can't see a reason why the starter wouldn't work. Did you replace the bolts that hold the cover on with studs?
I reed to mill out 3 broken metricated studs, so I plan on rethreading the holes for 3/8 and using studs.
Yeah It has all the mods except the billet cover. It makes too much power for the puny cover. I can tell ya the "cover flex" is real. This is the second time it came apart. I'm tired of hot oil on the back of my neck.
I plan on running the CVT plate in a "divorced" configuration as also.
I plan on removing the balance shaft as well. I have not had any clearance problems with the ARC rod and balance shaft.
Thanks for the input/tips