D&B 3.7 Twin

Bore 36 MM Stroke 30 MM Compression Ratio 7.6 to 1
Carburetor Diaphragm pump type with accelerator pump by Walbro
Spark Plugs 14 MM BPM7A or 10 MM CM6 by NGK
Fuel Ratio 32 to 1 Recommended Klotz 308