Removing the Pulse Air Injection System

[Jeff488]

The late-model airhead filter is of similar construction to the filter my car takes, but is half the size and three times the price.

No doubt. However, BMW probably doesn't sell a million of these a year, so production costs aren't spread over so many units. But I reckon you already know that.
Besides, it's a genuine BMW part, having been lovingly crafted by elves(who punch in on a cuckoo clock) in the Schvarzevald!(Here's where the music fades in: "Duetchland uber alles")

 

[YLLIB]

I have often found that removing the stock velocity stacks that come in the square airbox kills midrange.

I have found that having two large air horns instead of one large and one small kills midrange.

I run my crank vent to the ground but be careful how you do it because the slip stream can pull it back up and on your rear tire and stuff.

Square air boxes should not be a crank vent sump. It makes a mess.

Oilhead sump drain plugs are excellent plugs for the air pump port on the heads.

I have serviced hundreds AND hundreds of late model square airbox beemers and I think that K+N filters filter dirt and dust WAY better than the stock filters. I have taken SO many stock filters out and that airbox looks like a litter box! I have seen photos of people testing clean and almost oil free K+N's and they wonder why they didn't filter well. READ THE INSTRUCTIONS. Don't clean them and keep them OILED. Guess what? Dry Uni filters don't filter either. I have seen that a lot as well. The internet K+N doesn't filter crap is crap! Go to the races. See what they are running. If you think every XR and DL out there is running K+N's because they don't filter you are an idiot. XR's anyway have plenty of room for about ANY type filter and those guys are spending hundreds of thousands of dollars trying to win a National Championship.

Square K+N's need to be modified or they don't fit right and suck dirt. The front will bow back.

I know a lot of experienced mechanics that don't know what they are talking about. Try to find one that does.

 

[20774]

...and those guys are spending hundreds of thousands of dollars trying to win a National Championship.

But how many of them are trying to get hundreds of thousands of miles out of the same engine block/top end? Much of those thousands of dollars goes into rebuilds of the engine in order to win that championship.

And something just seems logically wrong with those filters... Keep the filter/foam dirty/oil/etc. so that it filters better?? And how do you control the level of dirty/oil/etc. so you get consistent filtering?? What's wrong with that picture?

 

[YLLIB]

There is SO much money in professional flat tracking that the tuners wear their bikes out on purpose so they can rebuild them as often as they can? Get real!

I am familiar with a lot of runner up and one Grand National Championship effort. A lot of those races are won by inches. When those guys get an engine together that for SOME reason is a runner, the last thing they want to do is take it back apart!

Logic??!!?? There is no better way to get to the wrong conclusion with confidence.

 

[20774]

OK, my reality take is this...I suspect it would apply to a vast number of people who hang around here. BMW designed the intake and filtration system and exhaust to get the best all around performance, from idle up to redline. Most people never make it to redline or spend any kind of time there. They're not racing on the streets, so inches of performance are not important. Those racers you mention are spending 95% of their time at or near redline. I'll agree they need some airflow. But no one really needs that for the street, not on a consistent basis.

I think if you're going to tweak your bike, there are other areas that can benefit a lot by small changes. People have already stated that some changes might affect various ranges of performance. It's not all straightforward...just open up the intake and she'll run better? Hardly...everything has to work together. Most just want a reliable ride with a decent amount of longevity.

IMHO, I'd never do something like this which has the possibility of ruin the performance and requiring further dipping into my bank account all the while possibly subjecting the engine to detrimental debris, etc.

But there's always a small fraction of the larger group who want to go down that path. I'm just not one of them.

 

[pedrocasper]

"The Sting of Criticism, is the Truth in it." -- Benjamin Franklin

"All of civility depends on being able to contain the rage [and rants] of individuals."
-- Joshua Lederberg

I didn't think the question would raise such interesting and educational dialogue. I think I will just plug the PAIS, retain the stock air-box and move on. I have not heard that removing the airbox improves overall performance much, infact could dimish it in the midrange.

Maybe setting up a forced air system like the v-max engine is the way to go!? (Just kidding)!!!

 

[lkchris]

" I have not heard that removing the airbox improves overall performance much, infact could dimish it in the midrange.

BMW's middle name ain't motor for nothing!

 

[sumran]

The late-model airhead filter is of similar construction to the filter my car takes, but is half the size and three times the price.

Can't argue with your logic. However, compared to all the other money spent on parts, accessories, gear...

When I first started, I thought buying the motorcycle was the big expense. If it was just boring transportation, I'm sure I would spend much less. I never catch myself daydreaming about taking my truck out for a spin.

 

[YLLIB]

OK, my reality take is this...I suspect it would apply to a vast number of people who hang around here. BMW designed the intake and filtration system and exhaust to get the best all around performance, from idle up to redline. Most people never make it to redline or spend any kind of time there. They're not racing on the streets, so inches of performance are not important. Those racers you mention are spending 95% of their time at or near redline. I'll agree they need some airflow. But no one really needs that for the street, not on a consistent basis.

I think if you're going to tweak your bike, there are other areas that can benefit a lot by small changes. People have already stated that some changes might affect various ranges of performance. It's not all straightforward...just open up the intake and she'll run better? Hardly...everything has to work together. Most just want a reliable ride with a decent amount of longevity.

IMHO, I'd never do something like this which has the possibility of ruin the performance and requiring further dipping into my bank account all the while possibly subjecting the engine to detrimental debris, etc.

But there's always a small fraction of the larger group who want to go down that path. I'm just not one of them.

I use K+N filters on my own bikes because they filter much better that the stock paper ones. IF you modify them so they fit right and follow their instructions, I never even see a fine layer of dust inside my square airboxes and that includes multi-bike offroad rides with a LOT of dust. Can't even come close to saying the same thing with stock paper filters on the SAME bikes. I don't use them for performance. I don't think they make any difference. I have installed them on a lot of bikes and they never needed re-jetting. I use them because they filter better.

 

[spencer]

can someone explain how to modify k+n filters for proper fit on post-1980 airboxes?

 

[YLLIB]

Put your new K+N filter on the bike and mark it with a magic marker where it meets the starter cover. Take it back off and cut two indentations into the filter so that the starter cover will slide into the filter. I make the indentation from the bottom of the filter to just a bit into the curve of the starter cover where it flattens out and becomes the top of the cover and cut the grooves into the filter about an eight of an inch deep and a bit wider. Now when you install the filter it should slide over the rear side edges of the starter cover. This allows the filter's front lower lip to go OVER the front edge of the airbox like it is suppose to. I stick a tiny light into the cutout in the starter cover for the air pump vacuum line and look in between the starter cover and the air box to make sure the filter's lip is completely over the edge. NOW the filter can filter!

I say new filter because once the filter has been bowed back for some time the rubber filter body get a memory and it won't stay in the correct position.

Be careful. Exacto blades are dangerous!

 

[BUBBAZANETTI]

i know where you're trying to go with this..........

read: "traditional" BMW "cafe" setup is removing the airbox and putting on two little pod filters.

most of the people criticizing this idea are from the "function over form" mindset (NO offense guys!!)


i love cafe racers and am thinking about building one myself this spring. my last airhead had drop bars, bar ends and a slightly modified rear end, nothing too crazy. i'm of totally mixed feelings over the way the airbox removal thing looks. on one had it does follow the cafe ethos of "minimalism" but on the other hand, it looks like someone kicked a big chunk out of the engine, since (and esp on the aluminum airbox model) the airbox follows the lines of the engine.

i would say marginal gains in "looks" (again opinion) and weight (who cares) wouldn't out weigh the change in performance.

btw, one cool thing you can do to your 84, which i did to mine, is remove the license plate bracket and install the plate vertically, very "cafe", very "slimming", cleans up the rear end. if chopper dudes can attach plates vertically to the transmission case, anyone should be able to, hahah

 

[pedrocasper]

cafe

Yeah, I understand your desire re: cafe bikes. I posted pictures of my R100 in the airhead post a picture thread, so not to do it again, here is the link:
http://forums.bmwmoa.org/showthread.php?t=2140&page=48

As you will notice, I have an aftermarket cowling (solo seat) and a license plate holder slim and modified. If you are interested in cafe bikes, check out the other forum I blog on. Lots of cafe vintage roadracer folks on that forum. I'd like to see more pics of your bike!

www.caferacer.net.

 

[The_Veg]

Also check out rockerboxer.com

 

[pedrocasper]

Also check out rockerboxer.com

Yeah, I proudly wear the T-shirt he sells! That is a great site. Full of inspiration.

 

[The_Veg]

The guy behind RockerBoxer is that Vanzen fellow who has posted here about his Old Cro project. I met him recently after knowing him via forum-posts for years. Great guy to hang out with and talk bikes.

 

[wpunch]

I have a '83 R100 with almost 49,000 miles, and I have been putting up with the damn oil leak on the back side of the carbs since the bike was new! Why?? I don't know!
I am REALLY ready for a fix that works.

There are a couple of different ways described here, to solve the problem.
My question is, does this really work? Is there any more oil seepage/leaks?

My 2nd question ...
I just noticed the left side metal/rubber tube that runs from the jug to the engine block is corroded, just like the other side did a few years ago. I don't care to spend the bucks to replace it.
With the above fix, do I just leave the tube there?

Many thanks!

 

[pedrocasper]

The guy behind RockerBoxer is that Vanzen fellow who has posted here about his Old Cro project. I met him recently after knowing him via forum-posts for years. Great guy to hang out with and talk bikes.

Hey, why is the GS named "El Chupacabra". Come to think of it, there is no better name for a R1200GS!

Oil in Carbs. I am assuming that the leakage is because of how the crank venthose feds back into the air box. (just an assumtion). That was one of the reasons why I was thinking of routing the vent hose to a catch can or to the ground (with filter on it).

I purchased the UNI-Filter (Foam) for the standard airbox that I am retaining. I'll post pictures when the bike is completed.

 

[sololobo]

Oil in Carbs. I am assuming that the leakage is because of how the crank venthose feds back into the air box. (just an assumtion). That was one of the reasons why I was thinking of routing the vent hose to a catch can or to the ground (with filter on it). .

I pulled the the stock rubber lines off of the "T" fitting the goes through the airbox on the way up to the breather, then wrapped green scrubbie pads onto each side of the "T", used zip-ties to seal the end, and another to secure to the "T" fitting...

No oil found in the airbox yet, seems to work fine and doesn't force any oil/grunge into the carbs.

 

[robsryder]

Filtration by K&N air filter

Some experiments of various air filtration systems have been conducted with the results reported on the cited websites.

http://www.bobistheoilguy.com/airfilter/airtest1.htm
http://www.bobistheoilguy.com/airfilter/airtest2.htm
http://www.bobistheoilguy.com/airfilter/airtest3.htm

http://home.stny.rr.com/jbplock/ISO5011/SPICER.htm

After examining these websites you may wish to reconsider using K&N air filters.