Foam Air Filter Sucked Down Throttle Body!

[Arizona Wayne]

I recently got my `77 Convert. w/hardly used K&N filters, which I replaced with new Uni filters.  I'll sell them to you for $20 @ the National like new.    That's cheap for K&Ns.  Also will have a tall chrome 7/8" handlebar like new with cross brace for tall riders for $30.

[leafman60]

I will probably go to oiled cotton (K&N).

This could be like an oil thread. 

Regarding holding a K&N to the light-

http://www.thedieselstop.com/contents/getitems.php3?K%26N%20Letter%20to%20The%20Editor

I've used them and often had to re-jet after installation due to their increased low speed air flow.  Even some anti-K&N literature admit this feature. I've torn top ends down after 80,000 miles on a K&N and still had crosshatch marks on the cylinders.  No wear.  I've also never noticed dust stock to the walls of my airbox.

Free flowing

[drlapo]

I have a K+N filter in my BMW R80 and the airbox is clean
My brother put one in his car, a Mercedes, and the airbox was constantly dusty; the filter was passing fine dust
No problems with UNI foam filters in my triumphs

[Triple Jim]

Leafman, the effectiveness of filtering is often proportional to the pressure drop across the filter.  It's not necessarily good that K&N filters let air through very easily.

An interesting effect is that as air filters get dirty, their resistance to flow increases, but they actually become better at catching dirt particles than clean filters!

[Rough Edge racing]

  I had my Triumph 650 race bike on the dyno and tested it with 3 inch diameter  x 5 inch long Uni filters...There was a noticeable drop in power.  There may be different results on other bikes...

[Triple Jim]

  I had my Triumph 650 race bike on the dyno and tested it with 3 inch diameter  x 5 inch long Uni filters...There was a noticeable drop in power.  There may be different results on other bikes...

A drop in power compared to what?  (another filter, or no filter?) 

Assuming the added flow resistance made the mixture richer, did you try a leaner main jet to get the mixture back to correct?  It's possible that the reduction in power after rejetting may have been negligible.

[leafman60]

Again, I've used K&N for many years on a few bikes.  I have closely inspected and not seen evidence of dust/dirt infiltration.  Sometimes that can happen, with any filter, if the rubber seal is not good and has an air leak. I put a bead of silicone grease on my rubber filter seal.

[Rough Edge racing]

A drop in power compared to what?  (another filter, or no filter?) 

Assuming the added flow resistance made the mixture richer, did you try a leaner main jet to get the mixture back to correct?  It's possible that the reduction in power after rejetting may have been negligible.

  Compared to no filter. The drop in power was not due to a change in A/F ratio but just a result of less air...

[Triple Jim]

So the A/F ratio did not change?  That seems hard to understand with restriction added to the flow of a carburetor.

[Rough Edge racing]

So the A/F ratio did not change?  That seems hard to understand with restriction added to the flow of a carburetor.

 Well, jetting didn't restore lost power so I assume the A/F wasn't affected. You can't really make up for power lost to air flow restrictions if the engine can use all the air flow

[Mike Tashjian]

Putting a filter on a carb can change airflow through it and account for loss in power. No change in A/F mixture because the carb meters fuel to the air that passes through only.   A filter would need to be tested to achieve the results you are looking for.  I am sure the wrong shape can be detrimental to flow especially in a race engine.   Usually you see a nice horn designed to maximize airflow at high RPMs.  That said, I would not run a regular engine designed to have a filter without one.  Sucking a few bits of foam from time to time is way cheaper than an engine rebuild because you sucked a stone that bounced off the road through an open carb or throttle body.   Mike

[Rough Edge racing]

Putting a filter on a carb can change airflow through it and account for loss in power. No change in A/F mixture because the carb meters fuel to the air that passes through only.     Mike

 It depends on the amount of restriction. In my case it was slight but enough to cut 5% of the power. If it was more restriction, it would greatly increase the vacuum signal and richen the mixture a lot. Like what a "choke" does...

[Mike Tashjian]

Exactly right, all modern carbs are designed to not be bothered by slight restrictions that a partially clogged filter would present. But if you are trying to go as fast as possible that small percentage is all the difference in the world.  Mike