Hi,
First you must completely close the oil vent tube coming from the side of the motor, as it is a lesson on how not to vent the crankcase. I learned in the 1st grade about reducing the size of a hose and increasing the pressure [Squeeze a water hose and watch how far it squirts the water]. The passages in the rear of the motor are way too SMALL, and must be shut down.
The NE cylinder you have has a hole that lines up with the slot in the crankcase, and vents into the tappet cavity to allow the pressure to exit. Once the oil/air mixture is in the cavity it must be separated, and the oil returned to the crankcase. You will need to make a working vent system to reduce the crankcase pressure, and can be made form EZ to find parts. The hoses needed to connect the vent system and retain the mesh and PCV valve can be purchased at most auto parts stores. Need 2 sizes of heater hose [must be able to handle hot oil], some metal mesh [a pot scrubber without soap], PCV valve for small Ford V8, and an elbo [can use pluming fixtures], and a few plastic ties. You will spend around $25.00 plus some time to make the vent system. I made several hundred of these and sold at cost, for those that didn't want to go to the trouble of making their own, however I don't have any left, so........ make your own.
As stated in an earlier post the 26 MM carburetor must be setup completely different to work on the Whizzer motor correctly. Of the 20 or 30 I have had to work on, none evry worked as well as the original supplied by Whizzer USA. You will only be able to "dial it" in close, never equal to the original.
Normally the throttle response is fair up to 3/4 throttle where the main jet takes over, however it sounds like it doesn't want to accept fuel at lower setting, therefore you will need to work on the size of the Pilot jet first. Sadly, I don't know if you need a larger pilot or smaller, as the symptom is the same for both scenarios. If it has a #32, try a #35, if it has a #35, try a #32. Also adjust the needle settings to see if it helps the throttle response. If the needle is too high the motor should "8-stroke", and if too low it will run too lean and could cause motor damage. Best to try settings from middle to one each way. Keep raising needle until it "8-strokes", and then drop one.
Hope this helps.
Have fun,