I found that putting a overbore kit on a engine will not necessarily increase the rpm but it will increase the torque of the engine. AV7 stock crank is good to 10k before it wants to come apart, just the added weight of the piston and torque will give more vibrations.
If you have upped to 15mm carb then use a 15mm intake (or larger) and check the intake is 15mm right through, if it is cast intake then there is a restriction where it transitions between round and rectangle, you want to chase a 15mm drill through the bore to make sure it is open, or carefully with a dremel.
I usually run rich so I can ride all day long and into the night, mid 70s jet works well on a 70cc kit. Best practice would be to have jets in the 70s range, suf in a fatty and get the engine up to temperature and run it hard at wide open throttle. If it 4 strokes then come down 2 sizes and take her out again for a fast hot run. When you find the fattest jet size that does not cause 4 stroking at WOT then you are good. Some folks argue to go leaner but this is good safety until you feel you know the bike better and you maybe want to experiment. Lean makes more heat so the engine will pump out more and more power until it is so lean it seizes.
Check the outlet of the exhause, if the ID is less than 11mm it is undersize and causes a restriction. Exit pipe at 11mm is a goodly size for a 70cc motor if you are streeting the bike. If you are tires of packing getting all gummed up in the silencer you can replace it with course steel wool or make a new baffle with a piccolo tube inside a piccolo tube to diffuse the sound.
Check your timing, you want to be in the 1,2-1,5mm BTDC range, this will keep theheat down as well as give you acceptable starting, idling and power. If you have a CDI ignition set it at 1,2mm for thebestbang for the buck.
If you are still on points, do the external condenser mod if you have not done it yet. Also make a piston stop tool to help with the timing setting, do not try to adjust timig by messing with points gap, it needs to be 0,4mm to ensure exciter coil saturation.
Always replace the bonding strap between the motor and the frame. Best suggestion is to use a wire to go from one of the intake studs to connect to the lower external coil stud.
If you are on WOT all the time then gap the plug at 0,38. If you are doing stop and go city/suburb open them up to 0,46 so they do not foul easy at idle and low rpm. Lots of factors in selecting plugs, go for B8HS thru B5HS range, select the coldest plug (higher number is colder) that does not foul at low rpm. Hot plugs can get on a glow at WOT and cause detonation and kill your motor.
For urban-suburb riding, the top engine mount on a Moby likes to be just snug and use a nyloc nut. If it is too tight then the radial torsion on the rubber will finish them in short order. Tight just enough so there is no side to side play but loose enough so the engine will swivel. If you are at WOT al the time then swing the engine in to where it sits at full variation and tight the long bolt goodly, that will allow more vibration dampening at WOT.
Hope some of that helps.