K&N Filter

I use a K&N air filter, part number HA-0002, on my ST1100. The current part number specified by K&N is HA-1191. Apparently the newer version comes with a foam outer band. This foam band has been found to cause performance problems on the ST1100. Read what Simon Clayfield went through before he figured this out:

"Hi Mike,

"I don't know if you remember me, I contacted you a fair while ago seeking advice about an annoying flatspot in midrange on my 2000 Honda ST1100. I tried practically everything like changing coils, leads, caps, plugs and full inspection and testing of the electrical connectors. I checked the valve clearances and cleaned the carbys thoroughly, checked the diaphragms, set the float levels and checked for air leaks etc. I recently purchased a used ignition control unit and swapped it over all to no avail. So for nearly 2 years I've ridden around the flatspot by changing down gears for overtaking and climbing hills, etc., and tolerated the bike's performance issues, forgiving it because of its many redeeming qualities.

"The other day I was servicing and cleaning the bike getting it ready for our annual hospital fund raising ride. I inspected the air filter holding it up to the light and I couldn't see light easily through it. When I removed the foam band you could easily see light. Holding the foam band only to the light it was difficult to see light. So I thought I'd leave the foam band off the air cleaner and see if that made any difference (it and the air filter were clean). I had replaced the air filter with a K&N item when I purchased the bike a couple of years ago as the previous owner supplied this and other sundry items including 5 litres of oil, 2 oil filters and a new battery with the purchase. The new K&N filter was supplied with the foam band but the filter I replaced didn't have one.

"Well I can't believe the transformation it made -- the engine runs faultlessly and pulls with strong power from idle right through the rev range without so much as a flutter, it's fixed and I'm as happy as a pig in mud! Please tell your mates and put this tip on your website. I've saved myself some money as I was ready to purchase new needles and jets although they appeared to be servicable with no signs of wear. This problem explains the sudden richness of mixture as soon as throttle was applied at mid range.

"One very happy ST1100 owner, Simon Clayfield "

I searched the web for st1100 k&n foam and found other instances of the foam outer filter causing problems, so if your ST1100 has the foam on its K&N, you might want to try removing it.