Speed Kits are typically aftermarket cylinders produced by performance part companies. These are usually moped-specific, have different port maps than stock cylinders, and sometimes a different displacement. These differing port maps and displacements allow the kits to improve the performance of the moped they are installed upon. Kits can range in displacement from 49cc, like the stock displacement, on up to 90cc.
How Kits Improve Performance
- Larger intake, exhaust, and transfer ports are common.
- Reed valves are sometimes added.
- Boost ports, or extra transfer ports can be present
- Piston cutouts, different piston rings, and different piston ring positioning are also common.
Typically kit cylinders will have larger transfer ports than stock cylinders. For this reason, it is important to machine the transfer port cutouts in the engine cases to match the transfers in the new cylinder to take full advantage of the kit. This is known as case matching. See Rebuild a Puch E50 Engine for a quick case matching tutorial.
Kits and Performance
Since kits drastically change the performance of the moped, it is extremely common to supply them with larger carburetors to supply more mixture for larger displacements. Because kits greatly change the fuel mixture needs of the moped, it is CRUCIAL to re-jet your carburetor to meet these needs. Other common performance enhancements include as expansion chamber exhausts and performance cranks. Kits are typically the most expensive performance parts you can put on your moped.
Larger displacement kits sometimes require widening the opening in the cases into which the cylinder sleeve fits. This allows the engine cases to accommodate the larger bore necessary to achieve the higher displacement.
Note:The kit alone does not determine the top speed of your moped. Many, many other factors, like those mentioned in this article, also greatly affect top speed. Just because someone has the same kit as you does not mean that you will go as fast as they are going.
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Breaking In a Kit
Since kits are usually purchased new, they need to be broken in carefully before running full throttle for any extended period of time. Incorrect jetting, air leaks, and improper or insufficient break-in can lead to seizure, which can frequently make an expensive new kit completely useless.
Main article: Kit break in guide