Runs poorly with air cleaner housing on

This is in regard to a 98 Craftsman yard mower with a 15 1/2 horsepower Kholer.

This motor runs rough with the air cleaner housing on. If I remove the air cleaner it is only a very tiny bit better. If I remove the entire housing, it runs great. The air cleaner is new.

I have removed and cleaned or replaced everything in the fuel system. The fuel tank has been cleaned. The fuel lines and filter have been replaced. The air cleaner is new. The carb is new.

There are not any adjustments on the carburetor for air or fuel, that I can see or am aware of. There is an idle adjustment but it only alters the positioning of the throttle arm to affect idle speed.

Why may I be experiencing this problem?

Have you done a compression check and leakdown test on the engine?

I think the air cleaner housing is touching/binding some of the linkage.

Air cleaner housing maybe rubbing the governor or throttle linkage.

Have you experimented with the air cleaner by lifting it on and off running?

Does it change solely by the presence of the cleaner, or the screws holding it?

Will cupping your hand around the carb do the same thing?

Sounds like possibly a defective carb. Will the original carb work at all?

Compare the original with the new. It will take a very close comparison, checking drilled ports, air bleeds, etc. Sounds like maybe something is wrong with the choke circuit. Or it is picking up slight atmospheric differences due to possibly a bowl vent issue. Especially if it turns rich when the cleaner is on.

1998? Would that make it a single cylinder Kohler Command series engine?

Carburetor is new? Is it the exact right original equipment replacement for that model and spec. of Kohler engine? About four times last year our shop was asked to 'fix' a engine with a new carburetor the customer bought online. While most of those carburetors do seem to give pretty good service, there are occasionally some that just don't work right. And in my experience, it is very difficult to pinpoint the reason they don't work. And OEM parts don't fit them most times. Of those four times, only once did we make it work at all and that time the other mechanic just kept drilling the jet bigger until it ran 'fairly' well. Its performance never was something to brag about.

A couple other things to check: Does the air cleaner or any of the gaskets cover any of the small holes in the carburetor faces? Check the flange of the carburetor that bolts to the engine or intake adapter too. And the other thing that messed me up a week ago was the carburetor adapter gasket with too big a main hole in it. This allowed the engine to pull in extra air from the vent passage in the carb. body as the large hole in the gasket was about 1/4 larger than the hole in the carburetor.

Are you sure you have the right gasket on the engine? I had a new engine that had the carburetor gasket on backwards.

Sounds to me like your "new" air cleaner is defective. Not the first time, especially if it comes from the home of the Wuhan Flu.