Not sure which type of carburetor you have? Watch this video for and easy way to figure it out.
Marine, Mercury Marine in particular used Rochester 2 Jets and later Mercarb carburetor on their engines. They are both 2 barrel and often are confused when ordering parts.The best way to tell which one you have is to look at the idle mixture screws, or in the case of the Mercarb, the one idle mixture screw. That is all you have to do to determine which one you have. The one screw on the Mercarb sits in the middle of the throttle body.