1985 235 power head swap

[1973johnson235onabassboat]

So the power head on my 1979 Johnson 235 had some pretty bad engine damage from failed rings. I bought a used power head online which appears to be from a 1985 235. Engine is identical besides the exhaust cover, same bubble back style just a spot for something to mount on it. I only got the block so I installed the flywheel, ignitions system and carburetors to the newer engine. The motor runs great just the idle is way to high, even at the lowest setting. I suspect the difference in idle rpm is a carburetor issue. I know the carbs are different between the years but I thought it would work. I know the old block was a 3.5 diameter piston while the newer one is a bigger piston with less compression or something. Did I make a big mistake? Seems like I need smaller idle jets. Thanks for any input!