Welcome to the liST! Before Posting,  READ the liST rules stickie post Here! This is a private, STOC-members-only forum. Your real name and STOC# must appear in all posts. Failure to comply with these rules may result in your profile being changed, your account being suspended and/or your posts being removed.

Main Menu

Sub Air Filter ( ST1100 ) *

Started by KoTAOW, March 27, 2009, 09:17:23 PM

Previous topic - Next topic


Sub Air Filter

Original article on Mike Martin's web page here:


Have you ever noticed the little rectangular box at the front of the air cleaner housing? The one with two hoses attached to it and running to the carbs on each side of the engine? That box is the sub air filter, and houses a foam element about 2 1/8" long by 1 7/16" wide and 3/16" thick. The element filters air that goes to the back of the carb diaphragms.

I had the air filter housing off the bike and happened to peek up into the opening on the underside of the box. I could see that the foam filter element had deteriorated and a chunk of it was missing. The part isn't a regular maintenance item, but I suppose 15 years is longer than it should be expected to last.

You can access the foam element without having to remove the air filter housing. Disconnect one of the two hoses from the sub air filter housing. Then depress the tabs on the front and the back side and pop the cover off.

For a temporary solution, I snipped an appropriately sized rectangle from some open cell foam packaging material I had on hand. The material was 1/2" thick, so I had to cut it thinner. A utility knife almost did the job for me, but I wasn't able to control the cut. Scissors worked better on my second try.

Next time I order some parts, I'll pick up a new sub air filter element - 17253-KT8-000.

Update #1: Eric Russell tells me, "I've done similar. One can buy foam air cleaner material at the hardware store - look in the lawn mower parts section." Thanks, Eric!

Update #2: I subsequently discovered a lack of performance on my bike. After numerous attempts at getting it running properly, I finally discovered some of the carb diaphragms had developed holes in them. This would have caused an increase in airflow through the sub air filter, and possibly had something to do with it failing. Just thought I'd give you something to ponder....... There's a write-up about that problem here.

Last updated on December 20, 2007     © 2006 M. E. Martin, all rights reserved.

Thank You again for your contribution Mike Martin