Airbox Gap
 

Cub 1250, finally got all my parts in the mail and got the airbox squared away. Put a black rubber seal on the outside can like factory.

For some reason I was thinking the outside can would squeeze against the the inside plate and create a complete seal to the outside world. Air would only get to the filter from the fan (no more spiders able to get in there). But there's an obvious gap once tightened against the filter.

Is there supposed to be a gap, and if so, what was the stock gap supposed to be when these things ran off the assembly line? Right now it's about 1/8" all the way around. Was thinking about positive pressure on the throttle body.

https://i.ibb.co/w7FTYWn/20241008-112438.jpg

Wrong filter, sorry I don't have model #'s for you.

Thank you! Glad to hear this, I'd rather have a tight seal to keep out bugs.

The filter I used was this one:
https://www.amazon.com/dp/B0D1718C4V...fed_asin_title

States it's compatible with the 1250, but I'll order a genuine Kohler. Any chance you do have the correct filter number that you could share when you have more time at hand? There are so many superceding part numbers, I don't know where to begin.

Maybe I haven't seen them all, but all the Quietline air box's I've seen are not shaped like that, they are shaped like this.....

That's the lower half of the airbox. I think it looks the same, but maybe I'm missing something.

https://i.ibb.co/mB4mNfr/20241008-163642.jpg

My bad, the first picture kinda looks triangular.
Second one looks correct.

Yeah, you're right. Kinda looks like a guitar pick from that angle, doesn't it? :)

If anyone has the correct Kohler part number for the air filter, I'd be much obliged.

According to the parts lookup (yellow box at the top of the page), the part number is KH-47-883-01-S1, which replaces 759-3547.

Thank you sir. I finally sat down last night and figured out how to use that parts resource up top. It ain't the easiest to navigate, but I can get to my tractor now.

I did a little digging and the factory correct filter listed above is 1 3/4" tall. I measured my filter and it's the same size.

https://i.ibb.co/fQB3BVG/20241009-151121.jpg

You guys are sure it's supposed to sit flush and force air into the carb?

The Every Cub Cadet owner should know how to use the parts lookup. It’s a great resource, and It gets easier after you use it a few times.

I’m pretty sure the air cleaner cover on my 1450 (should be the same as your 1250) fits tight against the plate. I’ll take a look at it tonight and get some measurements for you.

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 !

This is interesting! I note that the part numbers for the air cleaner box ARE Kohler part numbers. Was Kohler connected in some ways with Cub Cadet to produce the Quietline series? I also wonder if these airboxes were specific to Cub Cadet and not other manufacturer using Kohler in their equipment?

The Kohler air tube is used on other applications than just CC.

Thank you IHCubCadet147, I appreciate you.

I looked at my airbox, and it measures the same as you and Ironman's. I think the only difference is the cheap Chinese filter.

I don't know if that's the case, the Chinese rubber is stiff. I just about have to bruise my fingers to tighten the wing nut to get to the 1/8" gap, and there's no give beyond that. Maybe it will settle with heat cycles, I dunno.

Your thought process is helpful though, appreciate you.

The season's over. I'll probably leave the filter I have on it to keep creepy crawlies out of the carb, and will probably order a higher quality name brand filter next spring. Thanks to everyone for helping (esp. for the pictures of measured parts), it's good to have a community. :)