Jason, Yes unbolt all 4 acorn nuts and clean out the screen, or check to see if its gummy. If it is use carb spray, the usuals. Then for now just bolt it back on, you wont pour oil out of it, you can also put some silicone around and no gasket for now till you get to the problem.
IF and this is a BIG IF as David suggest your exhaust was put in correctly, sealed and all.
The breather pipe, recirculates the unburnt fumes to the back of the air cleaner to be sucked back in the engine. If the pipe is missing all those unburnt fumes are floating around. No matter how sealed the bulk head is, by todays standards it will stink to high hell. Please leave the windows open till the pipe is reinstalled.
I can bet the pipe was discarded due to over fouling at the plugs from crap on the breather screen and not enough fresh air......
Just MHO, but I think if EVERYTHING else is correct, that simple pipe is your cause. Yes the carbs might be rich, but that's a different deal.
Good luck. you can do what I told you in ten minutes......even with no experience.
