75 Mercury 850 cylinder temps

Recently got a boat with a 1975 Mercury 850 on it and the lower crank bearing went out. Replaced the lower bearing and housing and while I had it apart replaced the rings and water baffle plate. The person we got the boat from said he had carb work done. I found that the top carb had the main jet loose in the bore and that the venturi had fell into the reed chamber. Got everything back together and have the engine running with good water flow from site port but it seems that cylinders 1 & 2 build heat (not hot) but cylinders 3 & 4 stay relatively cold. When I kill spark to 1 or 2 I see a noticeable change in idle but when I kill spark to 3 or 4 only a slight change. compression and spark good in all 4 cylinders and all seem to be getting fuel. Is this normal or could this be a carb issue that I'm dealing with?

Thanks

Re: 75 Mercury 850 cylinder temps

Are the lower spark plugs real clean? If so, they may be getting water in them from bad crank seals or leaking water jacket cover seals.

As for the carb, you are saying that the main nozzle, fell into the carb base, and the plastic venturi made it past the throttle plate into the crankcase? Seems kinda strange.

Re: 75 Mercury 850 cylinder temps

I have only run the boat with the water jacket ears hooked to it, haven't taken it to the lake yet. I have replaced all the gaskets and the baffle plate in between the side cover. I also pulled the plugs and cranked the engine with the water running and checked for water in the cylinders, doesn't appear to have any in it checking it that way.

As for the carb yes that is exactly what happen, I'm guessing whoever worked on the carb didn't install it properly as I had to repair some crossed threads. This was the carb for bank 1, 2. This is why I'm asking if I have a crab issue or if I have an issue at all. I plan on taking it out tomorrow and see how it runs under a load, just don't want to find I have 1 bank to lean or rich and hurt the motor.

Re: 75 Mercury 850 cylinder temps

Did you check labyrinth seals on the reed block on lower cylinders? Usually if upper/lower bearing fails (not just noisy) it will wear the labyrinth seals as thats the only support for crank in that area.