As far as the casual motorcycle or ATV owner is concerned, the fundamental difference between two-cycle engines and four-strokes is that oil must be mixed with the gasoline on a 2-stroke since they have no crankcase lube to keep things sliding nicely against each other. 

The actual combination of fuel and lube is done in a couple ways. The traditional simple method is to mix the lubricant directly with the gas, which has the inconvenience of requiring a separate container to store your "premix". The more modern, technologically superior approach is to inject the oil directly into the carburetor. This is done via a small engine driven oil pump which changes its oil delivery rate based on engine speed and throttle- the higher the speed and more open the throttle, the more oil is injected. Great idea, given the convenience factor. But there are some considerations to keep in mind...

First off, there's arguably no single more critical engine system than the oil injection system (at least a close second next to the carburetor). If the oil injection system goes down, might as well scrap the motor. Not only will the piston and cylinder be toast, but the crankshaft's condition should also be questioned as well. A second consideration might be improved control of the fuel/oil mixture. Of course, with premixed fuel the doubt about the oil injection's system performance is eliminated, and you can dial in the optimum mixture based on engine tune, riding style, oil type, etc. And lastly, the real estate occupied by the oil injection tank can be utilized to fit a tuned exhaust with a sizeable expansion chamber on competition or modified engines.

With the fan shroud removed, the oil injection pump can be seen near the bottom of the engine.

Having said all that, let's take a look at what it takes to remove the oil injection system from the typical Asian mini-quad. Fortunately, these machines are so nearly identical that the process covers 50s, 70s, and 90s and encompasses all the Chinese and Taiwanese machines such as Polaris, Eton, Kasea, etc.

Step one is to remove the fan shroud from the right side of the engine. Use a vise grip to clamp the line coming from the oil injection tank, or pull the line from the injection pump and quickly put a small screw in the end. Next, remove the oil tank. This can be complicated by the rear bodywork which may need to be removed. 

The absolutely correct way to remove the oil pump is, well, to actually remove the pump. But this can be a real pain to accomplish since the pump is attached the case with a couple small phillips head screws that are likely seized. You can, however, leave the pump installed, but disconnected. Behind the fan and flywheel the pump is driven by a nylon gear. Worst case scenario is the pump eventually seizes and the nylon gear strips, and the pump stops spinning. Problem solved. Otherwise, if you can manage to remove the pump, then you'll need to pull the flywheel and pull the nylon oil pump drive gear. Then, you'll need to plug the hole left by the pump. The choice is yours.

If you choose to leave the pump in place, remove the oil supply line from the tank (if not already done), the oil line to the carburetor, and throttle cable. Replace the fan shroud.

You'll need to block the oil injection port at the carb. To do this, purchase a vacuum plug from your local auto parts store. Buy one that fits real tight, just to make sure it doesn't come off.

The last part of the job is to replace the throttle cable assembly. The throttle cable on these machines is "Y"-ed.  Pushing the thumb throttle lever has two effects: the carburetor slide moves, and the oil injection pump cavity is enlarged. Do not make the mistake of simply disconnecting the oil injection pump end of the Y cable. This results in an asymmetric or unbalanced cable pull tension at the Y, and the little piston inside the connection point at the Y will cock and jamb. The unfortunate consequence is a stuck OPEN throttle. Obviously an absolutely undesirable situation for an unsuspecting rider, and potentially extremely dangerous. A "single-pull" cable is available from most of the mini-quad performance outlets that solves this problem and has the advantage of easing the throttle tension, thus relieving some of the thumb pump some riders experience.

To install the new cable you'll need to remove the carburetor and remove the slide from the top of the carb. Compress the slide spring and replace the old cable.

To finish up, drain your fuel tank and mix up a batch of 32:1 fuel, and enjoy your new peace of mind.