PURPOSE: To protect pressure detectors from fuel, lubricating oil and water by providing pressure detectors to a vehicle body frame above an engine, and communicating the same to a crank case via pipes, in an article for deciding fuel injection quantity based on variation quantity of internal pressure of the crank case.

CONSTITUTION: Crank chambers of respective cylinders 38, 40 are independently formed in a crank case 42, in a crank chamber pre-pressurizing type two cycle two cylinder engine 26 having a front cylinder 36 and an upper cylinder 40 and equipped on a motor cycle. Utilizing that internal pressure of the crank chamber corresponds to the intaken air quantity, respective crank chamber internal pressures are detected with pressure detectors 92 (92a, 92b), and fuel injection quantity is decided based on these pressure variation quantities. In this case, respective pressure detectors 92 are mounted via rubber dampers 94a, 94b of a frame 10 above the engines 36. Respective pressure detectors 92 are communicated and connected to right and left outer side face of the crank case 42 with pipes 96a, 96b, and made to generate electric signals corresponding to crank chamber internal pressures.