Working on a scooter

A while ago, I became the owner of a la souris scooter. I got it for free, because the owner claimed that it was broken. But when I started diagnosing the issue, it instantly became clear to me that the most significant issue was the fuel that I think was diesel, or otherwise extremely stale. Mixing it with proper fuel did the trick, and the scooter ran. But it ran inconsistently and had top-speed of only 25 kmph. Yes, almost any bicycle goes faster than that.

That is why I decided to attempt to increase the top speed. I soon discovered that many of scooters, called “Chinese GY6 scooters”, were made in a handful of factories, shared many parts and where decently well documented online.

Since the top-speed of 25 is comically low, I wanted to increase this to a more usable number. This is very simple on a GY6 scooter, as usually it consists of swapping the ECU. So I ordered a new ECU online, only to discover that my unit came with an ECS (electronic carburetor), and that replacement ECS’s are stupidly expensive. An image of the ECS can be seen below.

The ECS unit limit their speed in two ways:

The RPM is hard-limited, and the ECS will not produce more than a certain amount of ignitions per (time_interval)
The CVT is limited

The RPM Limit can be circumvented by getting a replacement CDI unit, which translates the ECU ignitions signal into real ignitions. The replacement CDI will simply produce more sparks than the ECU asks for, and mis-reports the feedback to fake the ECU. The CVT is shared with other models that do go faster. But the limited ones use a different bushing that limits the highest “gear”. Replacing this is simple, but you do need a few specific tools to undo the mounting bolts. For my unit, the torque required to undo the castle-nut was stupidly high and destroyed a cheap ratcheting wrench.