Hi lasvegasazguy,
EZM uses a different primary ratio than other companies, therefore the rear sprocket must be larger to compensate for the primary ratios.
The reason some of the 49 CC 4-strokes are dropping the rod is because of the wild ratios offered by several companies. It is like running your car in low gear all the time, while it will take off faster, it will also allow the motor to exceed 9000 RPMs [not a good idea for an extended time].
The Q-Matic used on the EZM kit is geared to make the bike a "cruiser", not a "pocket rocket", and therefore it will take off slightly slower, but the motor is only turning 6000 RPMs @ 30 MPH. Some of the current 4-stroke kits [offered by other companies], while taking off quickly, the motor is turning 9700 RPMs @ 30 MPH [redline is 7800 RPM].
Since the 4-stroke kit is a one speed, we elected to use ratios that would enhance motor life, make crusing speeds smoother, and while it doesn't "launch" from the stop sign it still has resonable "take-off" speeds.
If you need a different ratio [hills, extra weight, pulling a trailer, etc], a few have opted for the 60 or 62 tooth sprocket. We only stock the 56 tooth, however several companies offer "hub" adapters with a selection of sprockets ranging from 56 to 72.
We suggest you completely break-in the motor, as it gains a lot of power in the process. Check crusing speeds [normal riding speeds] to see if you adjust to the ratios, or need soemthing different.
I will list the RPM range on optional sprockets, so you will be better informed in the process.
56 tooth 7800 RPM = 39 MPH [redline]
60 tooth 7800 RPM = 37 MPH [redline]
62 tooth 7800 RPM = 35 MPH [redline]
64 tooth 7800 RPM = 34 MPH [redline]
66 tooth 7800 RPM = 33 MPH [redline]
68 tooth 7800 RPM = 32 MPH [redline]
72 tooth 7800 RPM = 30 MPH [redline]
Have fun,