Some years ago a BMW specialist and good friend made a few modifications to my K100. This vacuum tube with condensation and load valve made a huge improvement. But he told me even just spreading the vacuum across all cylinders makes a big improvement.
[url=https://servimg.com/view/20091290/9]

The photo cuts off part of the assembly on the left side.  Is it a condensation drain that is missing?  Interesting.

The main body finnishess about another 10mm on the left just off screen. The filter collects the condensation and then delivers it back at higher RPM across all cylinders. The nut you see is a drain plug. These engines have a few problems related to difficulty in starting after long periods. I believe the condensation build up in line on original design when vacuum is on the rear cylinder only coupled with a low batterie will prevent the engine from coming to life. I tested the theory once after being of the road for a while. When I undid the nut some liquid ran out. The bike then started after that on a low batterie. You can pull the hose off the end cylinder on original set up for a low batterie start. It will fire with a poor idle and then you can pop it back on.
Another plus is the starting now, it comes to life instantly in any weather cold or hot motor. 
Spreading the vacuum across all cylinders and disconnecting the TPS is also an important upgrade. Trust me it will be smoother and more responsive than ever.
My old mate had a stroke last Xmas (big loss in his industries) I’m lucky I got to learn so much from him.
Cheers 
Porto

Has anyone tried this, not so much the water filter but the vacuum hoses.

G'Day- I have this vacuum block setup ordered and on the way. Seemed easier to order all the bits as a kit from Amazon than drive around town and building a unit. I can report on the this once arrived and installed. 

Thank you Bricklayer, I look forward to the results cheers

That will work good mate. I've mated my four port vacuum with new updated injectors and adjustable fuel pressure regulator. Better than ever. That one you have in pic will look better aswell, than my one.

the only problem with the k100 starting is low battery , i have never had any other problems hot or cold , is this a common problem and i have been very lucky

Porto, do you still balance the throttle bodies after installing the vacuum chamber? 

Do you tune the fuel pressure regulator or just set it to the factory spec?

Are there any issues with backfiring when coasting after removing the throttle position switch?

Are the injectors you are using rated for the same flow as the OEM? 

Is there any measurable improvement in fuel efficiency?

My K75 has a bit of a stumble/hesitation coming off of idle if I don't roll on the throttle slowly that I just can't seem to get rid of.  Do these modifications get rid of throttle lag?

Gryph some members have had success eliminating the off idle stumble by raising the idle speed to around 1100 RPM.
Regards Martin.

MartinW wrote:Gryph some members have had success eliminating the off idle stumble by raising the idle speed to around 1100 RPM.
Regards Martin.

I don't really like that high idle speed that is really above the idle speed range of 1050rpm.  Right now, the only time it is a problem is when I'm not careful about rolling on the throttle.  I'd rather have the problem go away and still have the engine idle ar 950rpm.

It has to be solvable. The only time my 75 suffered that problem was on really hot days in traffic. Since fitting the heat shield the problem is long gone. Does the problem still occur on cold days is it worse on hot days?
Regards Martin.

I haven't noticed a pattern, it's mostly noticeable when I am acting immature on twisty roads, backing off and then cranking the throttle a bit too aggressively in turns.  Not a problem when I am smoothly rolling the throttle on as an adult would.

You could try richening up the mixture. What happens to the revs when you press the starter button when idling.
Regards Martin.

Hi PSF, just got up here in Aus.
After a lot of testing I settled at 14pound multi spray injectors. 2.5 to 3 bar pressure regulator setting. Vacuum across all throttle bodies. Disconnected the fuel cut off on throttle position sensor. Left the enrichment switch on throttle position sensor intact. Original MFS settings. Hotter plugs. 900RPM idle and throttle advance set up as factory. And this important. You must re balance all the throttle bodies. The original factory settings will no longer be accurate because of the years of use. You can do it easily, I just used a four guage vacuum. If you don't do the balancing you will sort every thing out around idle. There so much more detail you need and you can find it all here on this forum or other sites. Good luck and I'm happy to confirm and check things to help.

PSF You also listedso.e issues. I have none of those. The bike now with around 100miles runs better than it ever has before. There are some other things I've done. Will let you know if you like

I stay on top of the throttle body balance because it helps reduce the clanking as the engine goes through the 1500 to 1800 rpm range of engine speeds.  I usually check it twice a year, about every 2500 miles

I like your idea and am thinking of tying the vacuum ports together this winter and possibly getting an adjustable fuel pressure regulator so I can mount it in the air stream to help keep the fuel cooler. 

I think I'll also try disconnecting the idle function on the throttle position.  Might help the stumble since if engine is turning over 2500 rpm when I go to open the throttle there is going to be no fuel immediately available causing a momentary lean condition.

The bike in question has close to 100,000 miles and runs really well except for the mild stumble when I grab some throttle in a turn.  Starts, runs smooth, cruises happily at 100+, pulls strong up to 85-90mph, gets good fuel efficiency and uses almost no oil.  I don't want to mess any of that up.

Do it mate. Every one that has disconnected the TPS fuel pump on off has said they will never reconnect it. You can easily do it by knocking it out of adjustment. I cut the wire on mine, but that's just me. Leave the TPS connected because it has two other functions that are good. You will definitely benefit from an adjustable FPR. This is especially important when balancing across all four TB's and if you replace Fuel injectors. I settled on one with a built in guage on it and I'll never go back to the old style. Also if your in a hot climate then move the FPR to the left side back of the rail.

On the inside of the fuel tank you can replace the original fuel line with longer lengths. Position the fuel filter approximately half way between the lines on the right side. This will aid in changing the fuel filter on a regular basis. Will also help avoid breaking the spigot that the fuel hose connects to. I know two people that have damaged it, I'm certain there would be more. Make certain you use in tank submersible fuel line. Standard will break down within a few months. Also if it hasn't already been removed then remove the non return valve at the tank. You don't need it and they get noisy and seize up as well. Do these few things and make certain all the other basics are good! And your bike will be a pocket rocket that never stumbles again. Also I've removed the condensation filter from the balancer my mechanic friend made. The material and spring inside it rusted. There has been times when I've drain some liquid from it when I was using the original FPR in the original location. After moving the FPR to the out side I never came across any condensation build up again. Hadn't worked out why

A bit more on the balancing. You can see the effect it has when you have a fuel pressure guage connected. It is so much steadier. Also the vacuum to the FPR regulator is more accurate in signalling it to increase the pressure when you gas it. It all really does work well. I wish my mate hadn't had a stroke, he could get on here and unload all his trade secrets. I'm grateful he spent some time teaching me the small amount I know.
Best of luck and Merry Xmas
Porto

Thanks for the write up!  Pretty clear and when I think about what you're doing it makes sense.  Looks like I have a winter project once we get past the holidays.

Porto wrote:But he told me even just spreading the vacuum across all cylinders makes a big improvement.

The 4V Ks do that. Yellow part 15 below.

duck wrote:The 4V Ks do that.

Well, that just sucks.

Thanks Duck. I haven't seen that picture before.

Yamaha did something similar in the 1990s and announced it as something completely new and startling. They called it YICS - Yamaha Induction Control System - and quietly dropped it when it was found that it didn't really make that much difference to engine induction. It also made it a complete and utter pain to balance the carbs because you had to disconnect the carbs and then insert a special tool that blocked off the now-exposed ports. Said 'special tool' cost two mortgages and a gold mine, so when someone presented me with an ill-running YICS-equipped XJ750 for fixing about twenty years ago, I made one for about £2 .

Bottom line: can't speak for the 4v models because they 'come like that' from the factory, but for the 2V models, if you need to balance the throttlebodies, you'll need to disconnect the link tubes and block off the exposed inlets to get any sense out of the balance gauges. If you don't, you're going to be measuring the crossfeed between throttlebodies.

Hi Dai, there are no link tubes on two Valve biked when they roll out of the factory. But is common for bike mechanics to link them all up. Thats what happened with mine. As standard The factory has the first three capped and the end one connected to the FPR to increase the fuel pressure when you open the throttle. Balancing is easy. There are some good articles on here that explain it all. The best system I've seen and used is with four guages connected.

same here no link tubes and balance with 4 vac gadges , runs sweet 134,000 miles , uses no oil and pulls strong .

Porto wrote:Hi Dai, there are no link tubes on two Valve biked when they roll out of the factory. But is common for bike mechanics to link them all up. Thats what happened with mine. As standard The factory has the first three capped and the end one connected to the FPR to increase the fuel pressure when you open the throttle. Balancing is easy. There are some good articles on here that explain it all. The best system I've seen and used is with four guages connected.

I know. I was commenting on the problems that will arise for anyone that does decide to link the four vacuum stubs. I could have been a bit clearer on that.

I use a cheap home made two bottle vacuum comparator to balance my throttle bodies. 

Mechanical gauges, Bourdon tube or bellows, are the least accurate way to do this job. Unless they are calibrated to a standard they can read as much as 1-2% of full scale variation in readings from one to another.  To get better accuracy you would need to be using gauges with jeweled movements, and then have them calibrated regularly.  And even with that, parallax error when reading them will still prevent getting the accuracy I get with my $12 redneck balancer. 

With the comparator, I can let the engine idle for as long as 2-3 minutes, and not have the level in the bottles change, indicating that the vacuum on each throttle body is exactly the same, something that even the most expensive mechanical gauge can't do.  This is because vacuum differences that the gauges can't show because of friction and hysteresis will easily move fluid from one bottle to the other.

Sure, I can't read what the vacuum is, like I could with a gauge, but all I care about is that the throttle bodies are balanced and that the idle is between 950 and 1000 rpm.

Interesting way of doing it. I'm always fascinated by how many opinions and ways others have. Great forum this

Point well taken. The actual number is in this case irrelevant, you are merely comparing results. I made my own two bottle manometer, based on point-seven-five's pic, but it's too cold to test it out, no heated garage.  Once I figure out how to get a pic from my cell phone onto my laptop and then on this website, you'll have a pic. Can't wait to try it out. 
BTW. great series of posts on vacuum, including the post on the benefit of making a device to commingle the  four individual vacuums into one.

Bluebeemer is put to bed for the winter; maybe next winter it will be ready to ride in the cold weather.

i still make my own water level for any distance over 50 meters , its more acurate than lazer/dumpy , they look at me on site like i must be mad 

Hey firstly. I have a short 10 meter one I use a lot, it belonged to my Godfarther. It is a clear flexible tube with timber bungs at each end. Are you talking about the same type of thing?

yes water level . take one of the bungs out before you use it , trapped air , just tape to your stakes and you will have a mark to work from , worked for the pyramids still works today .

Hope I am reading this right, mine is a 4v, but I have caps on 3 and the vacuum on one, confused 

duck wrote:

Porto wrote:But he told me even just spreading the vacuum across all cylinders makes a big improvement.

The 4V Ks do that. Yellow part 15 below.

Garyk100 wrote:Hope I am reading this right, mine is a 4v, but I have caps on 3 and the vacuum on one, confuse

You're reading yours right.  

It's too cold to go look at my 16Valve RS, but I'm pretty sure that big manifolded rubber thingy is plumbed in above the butterfly, and thus doesn't really see the actual vacuum downstream of the butterfly.  If those big hoses were really balancing the vacuum, it would be impossible to balance the throttle bodies. 

I may be wrong, but I think it is plumbed to the crankcase and is an additional breather.  I can't say why the the old Z tube is still there if indeed that is the function.

Point-Seven-five wrote:It's too cold to go look at my 16Valve RS, but I'm pretty sure that big manifolded rubber thingy is plumbed in above the butterfly, and thus doesn't really see the actual vacuum downstream of the butterfly.  If those big hoses were really balancing the vacuum, it would be impossible to balance the throttle bodies. 

I may be wrong, but I think it is plumbed to the crankcase and is an additional breather.  I can't say why the the old Z tube is still there if indeed that is the function.

Good point. I think those rear ports on the 4V are above the butterflies. And the 4Vs don't have the same crankcase breatherr "Z" hose as the 2Vs.

There are photos of 16valve throttle bodies on eBay that show a 6mm port in the throat of the throttle body above the butterfly that connects to the hose barb that the rubber manifold connects to.

Point-Seven-five wrote:There are photos of 16valve throttle bodies on eBay that show a 6mm port in the throat of the throttle body above the butterfly that connects to the hose barb that the rubber manifold connects to.

You mean like the ones in the photo of post #35 here?   Anyway, to climb out of the vacuum hole and into the air, it seems the part that frankenduck implied was a vacuum manifold is likely to be a return-air manifold and it is connected to one of twin ports on the air box in a diagram and is labeled as an air return hose; the other port leads to an oil separator and is connected by a hose to to the crankcase, replacing the z-hose of the 2V models.

I'm almost certain we'll get Point-Seven-five's assessment when the crocus blooms.

Moby Brick Too is in storage for the winter on the other side of town.  It will be well after the equinox before I am messing with it again.

There's quite a bit of difference in the models. I'm liking the two valve more and more every day. Also ride all year here down under. The horses too.

My sexy new ChiCom vacuum block arrived from Amazon today during the Bomb Cyclone. It's -1F/-18C today (and dropping) so I will probably wait a few days before installing. Seems to have nice fit and finish but the threads will need some sealing to hold a vacuum. Thread pitch is 1.0 on the small male port nozzle with diameters shown in picture below (5.5mm & 7mm).  Nothing a little emery cloth on the nozzle to reduce diameter and a bit of warming on the hose to slip it on.

Taking advice on best method to permanently seal the threads (RTV Silicone, Teflon tape, epoxy, et al.)

Teflon tape.  Hold the fitting in your left hand and wrap in a clockwise direction.  This keeps it from unwrapping when you screw the fitting into the manifold.  Also, keep one thread(or two) between the teflon tape and the end of the fitting.  This prevents scraps of tape from getting into the plumbing and plugging something up.

Porto wrote:Some years ago a BMW specialist and good friend made a few modifications to my K100. This vacuum tube with condensation and load valve made a huge improvement. But he told me even just spreading the vacuum across all cylinders makes a big improvement.
[url=https://servimg.com/view/20091290/9]

You should only use black zip-ties on motorcycles. White zip-ties are used for arresting people and kidnappings.

Bricklayer I love that part. I'm ordering one now to replace my old home made job. Have you got a link you can share please.

Bricki we use a liquid sealer on gas fittings here that sets hard. It is the preferred over Teflon tape for fixed parts only. You can't undo it. Just a thought.

OK so I'm a knob. That is the link in your post. I've ordered. Thanks

Just being a devil's advocate here but what the heck is the benefit of this vs. having well synced TBs?








i

The vacuum cycle is more stable and improves Fuel pressure stability and pressure increase from FPR when required. You can see it with test equipment connected. There would be other reasons. It's standard in new equipment. That's all I can add.

Duck, it's possible that having multiple throttle body vacuum connections might unload the vacuum quicker when the throttle is snapped open allowing fuel pressure to rise a little faster.  This might have some positive effect on the throttle lag on some bikes like my K75RT.

I am going to try it, but will just do it with tubing and tee fittings at first.  The idea being that less volume will help response.