There is suppose to be a gap all around the cover. The filter is sealed when the cover is tightened and presses against it.

There HAS to be a gap, how else is the air going to get through the filter and into the carb!!
Geesh,,,,

Thanks IHCubCadet147 and DarkMinion. I'll run the airbox with a gap until I hear otherwise.

This is self evident on the older round style filter. If there wasn't a gap, how else would air get in! :)

But with the quietline models, there's the black tube that connects the airbox to the engine flywheel fan. This means that pressurized air enters the airbox from the back plate. If there's a gap, air will actually be exiting the gap at all times - because the fan supplies more than the engine needs. If there's no gap, air will be forced down the carb, kind of like a weak supercharger.

I'm not trying to be difficult, I just wanna know how it's supposed to be setup per factory.

Here are pictures from my 1200.
Yes, the a box cover seals all the way around.
The filter measures about 1 5/8" thick but it's older so the rubber seal is somewhat smooshed.
The depth of the cover is also 1 5/8".
When the filter is set in the cover you can see the flat edge lain straight across.
If you cover is not sealing at the edge I would look at the depth of the divot (for lack of a better word) where the stud hole is. Maybe it got deepened somehow and does not let the cover go down on the stud far enough??

Thru here.....

This pix shows a gap in the seal, is this some sorta relief valve when the filter gets dirty?

The gap is at the very bottom (6 o'clock position).
Probably to allow raw fuel to escape if the carb pukes.
Also, the rubber is old and surely has some shrinkage.

Thank you Ironman, those pictures are very helpful!

Seems like the filter height is the issue. I'll do some measuring when I get home tonight and see how everything stacks up. I bet if I put a flat bar across the filter sitting in the can it's not going to be flush like yours.

But that means that all future filter replacements will be too tall. Hmm.

I'm also curious to see what IHCubCadet147 comes back with. Anyone else have an old filter they can throw a tape measure on?

If the consensus is that the filter needs to be 1 5/8" tall, I'll have to search for a different filter. And if it is sealed, I'll need to open the carb needle some to account for more air flow so the engine doesn't go lean.

Ok, I got some pictures and measurements. My cover is tight against the backing plate. My filter is 1 5/8”, and I also measured 3 other used ones I had and they were the same. One had a number “Kohler 235116” on it. I had a new Napa Gold 2373, and that was 1 7/8”. My cover is also 1 5/8”.

A lot of overthinking being done ! The filter you have will work. It will collapse 1/8" when cover is tightened. The Gap in the rubber is from shrinkage. The rubber is designed to be twofold, seal for imperfections and also antirattle.
The name QUIETLINE gives us a hint as to the design of this system. It actually acts as a muffler to quiet down the noise from the intake. There is negligible pressure in the filter box as there is way more area for air to escape over and around the head and cylinder than there is in the hole to the airbox.
Hope this helps. Have a GREAT day !