Carburetor Venturi Size 506070 3 Cylinder Johnson Carb Body

Does anyone know the differenc

Does anyone know the difference between the 1996 3-Cylinder Johnson outboard carburetors? Is the carb body different or are just the jet sizes and timing different in the 50hp 60hp and 70hp engines? I would like to change my 50hp to the max hp the boat is rated for and need to know if I have to replace the entire carb or just upgrade orfices and change the timing and synch to get it up to the 70hp.


Thanks for your help

You may need to change much mo

You may need to change much more than the carbs. Like adding a crank with a longer stroke to start with.

"The crank is the same on all

"The crank is the same on all three models. The only parts that are different according to the parts catalog are the decals, cover color and carburetor. There are different part numbers for the carburetor assembly and the orifices. However, the carburetor body is not listed seperately so I am curious if the venturi size (or body) is different or if it is just the jet size and timing between the 50, 60 and 70hp models."

"I would think there is more t

"I would think there is more to it than just the jetting. A 20hp gain is not easy to get with just jetting.
If this was the case why would anyone buy a 70 hp when all they needed was a different set of carburetors or rejetting on the 50hp.
I've gone through my service books and of course there is not any real information on calibration of these carbs or details on what is in the engines, just how to repair them. That's OMC for ya. What is needed is a good parts book.
My guess is there is either something different in the porting in the cylinders and exhaust or the head is different. The bore maybe the same but are the pistons?
Again 20 hp is not easy to get from a two stroke engine. There is something other than the carbs. Did you check the cylinder,piston,reed part numbers?
There is a set of 65-70 hp carbs on eBay."