This is question we get asked alot, this is the easy
way to identify which one you have.Mercruiser has used several different types of carburetors over the years.
The Rochester 2 Barrel Carb was popular on the early 4 cylinder models and it
was also used on a few V6 and V8/305 GM engines as well.Rochester then stopped production so Mercury Marine designed its own version of the
Rochester 2 Barrel Carburetor called the Mercarb.The Mercarb and Rochesters were mixed in production models.
When ordering replacement carbs, kits or parts you need to know exactly
which carb your engine has. One simple test can distinguish between a Rochester and a Mercarb.
The throttle base plate of a Rochester Carb has two idle mixture screws.
The throttle base plate of a Mercarb has only one idle mixture screw.
If you have determined that your carb is a Mercarb, then there is one more
identification you need to make.
The Mercarb came with two different styles of accelerator pumps.
One pump rod was straight and cut off flat at the very top. This was the older style.
The other pump rod has a 90 deg bend at the top. This is the newer style.