Coleman fuel is 55 octane, small displacment (under 50cc) two strokes can use it, but if that engine has a decent CR it might not like the low octane.Flame speed has nothing to do with it, its all about knock resistance.

The brown diaphragm is for alcohol fuel it should with stand the low alky content in pump gas.

If the crank is not bent, then you just have to live the vibration. Sometimes low speed roughness can be traced to mixture issues.