The last important part of a good running engine is the crankshaft. Crankshaft intake timing is critical in determining the case fill. The longer the port remains open, the more fill that can occur and the more usable power that can be created. The shorter the duration, the less overall performance the engine will have. If the duration is too long, it will hurt the engine's ability to perform well.

When the crank intake port is open too long, the case loses the vacuum needed to pull the charge into the combustion chamber. When this happens, then engine cannot move the atomized mixture fast enough or far enough into the chamber to have an effective burn. This usually makes for poor starting with constant flame outs at low rpm operation with lower usable peak power and rpm.