Boxerworks.com

Hello All,
I'm planning to convert my '81 RS from flat to round filter configuration - basically for cosmetic reasons (sad, I know...)
I have procured an airbox with the 2 x 10 (edit: make that 12) holes at the back - and the appropriate starter cover.
The bike is fitted with 40 mm Bings - and my questions are;
- Will this conversion require changes in carb setting, new jets, needles etc?
- And - I know I'm walking into a minefield here - are there any disadvantages/advantages in using a well known after- market washable/reusable air filter (apart from the reusable aspect)?
Experience and opinions are welcome - thanks.
Dane

not too long ago I was getting the information to convert from round to flat. There is a lot of information on air flow advantages of each set up and opinions about the reusable filter. What I did learn is that many consider the round air box drilled to provide better air flow. The flat air box would be better if it could be made to have about 1/4 inch more in depth under the filter for increased flow. Reusable air filters? I like them! I really debated on this issue because I have a fresh motor and want to get the longest life out of it. I think that from what I've heard and read, the K&N filters are great, but you most likely will have to adjust the main jets. When I did it, I got a very noticeable improvement and increase in pep.

If I had a new engine I would never ever consider a K&N filter. Do you suppose that there is a reason that every vehicle manufacturer recommends a paper filter with the micro-pore technology? Maybe because they actually filter.

Duane,

Good to see you back on the forum. I've heard nothing but bad news about K&N air filters. What is your opinion of UNI foam air filters? I've read they do a much better job than K&N.

Sorry, I don't know that filter.

We gave up foam and mesh filters over 50 years ago.

You'll need coffee.

http://bmwmotorcycletech.info/K-and-N-filters.htm

Regarding any jet changes, while I only know about R45/R65's. When they changed from round to flat filters in 81 there was a significant decrease in main jet size and it seems to me the torque curve was flatter. When Itried using the later small main jet with an early round filter engine the mixture was grossly too weak even at midrange. I put it down to the flat filter type being a tuned intake system although they also went from flat tops to normal Bings at the same time and the R65 got bigger valves. Oddly this reduction in main jet size on flat filter introduction was not proportional across the range of engine sizes.

Don't know what that tells you except it may not be predictable. Safest option is to assume you may need to richen up as a result of the easier breathing round filter.

I use foam air filters in my dirtbikes, and they work great. Of course, I clean and oil them every ride, but they're dirt bikes.

Uni foam filters are great. Use "No-Toil" foam air filter oil. Oxy-clean laundry is what I used as a cleaner/solvent for the No-Toil oil. Cheap, works great.

Good luck.

SteveD, that page is great. It certainly makes it clear why K&N's are popular: they flow more air. Thus, K&N's are the most likely filter to require jetting changes. It also makes it very clear HOW the K&N flows more air: by letting in a lot more dirt.

I have seen the light with K+N filters.
I have used one for maybe 8 years and it is still in the bike.

At times, I have held the K+N up to the sun and.............marveled at the tiny little bright lights I could see here and there.
Even after a liberal spray of K+N oil.

Bright lights equal pinholes.

How much crap gets through those holes? Prolly doesn't matter to someone with a mechanical history such as mine.