is it possible to replace the rear sprocket to get the gearing you want, depending on ratio's 1 tooth on the front = about 3 on the rear
Yes. But I have to put another chain on. Trying to do it without that.
If you go to down in size on the rear you only have to shorten chain and if you go back to the original you can join the cut piece back on with a joining link.
The bit about the kickstarter is the fact that with the larger front sprocket the chain will come every close to the kickstarter shaft. If I get a chance I will put a 14 on a motor and check it for you.
Other possibility if you can't get a 14 is put a 14 tooth band onto an old sprocket by machining a 14 blank or something available out and then machine an old Bulto one down, then welding together.
It does get a bit expensive and can soften the case hardening with the welding heat, does work ok I have a 14t Maico done that way.