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    I have a 2 cyl 4 stroke spark engine with 0.75"dia pistons. Runs OK on one cyl ( one plug removed ). Both plugs in and one cyl. exhaust is cold. This occurs with either no. 1 or no. 2 plug out. Seems like one cyl. is starved for fuel?? What is the formula for calc. the size hole for the carb needle valve? Plans call for #70 hole. Maybe too small?
    I would think not. I have a 4 cylinder with .625 pistons and stroke and it runs well with the same size hole. #70
    I think it is close to the size needed by the Silver Bullet, and it runs quite nice in that size hole.

    Taking a wild guess - ignition, are the two plugs firing ?
    • CommentAuthordavid
    • CommentTimeJun 20th 2010
    As long as the intakes cycles do not overlap, the same carburetor that works for one cylinder will work for up to 4 cylinders with all the same dimensions. The carburetor actually stops working between intake cycles. I can see a carburetor problem being intensified by multiple cylinders.