Hi brick pilots.

For some time I have been looking at the vacuum fluctuations generated at the throttle bodies vacuum ports. Because the vacuum port is close to the butterfly edge the fluctuations are pretty wild. Has anyone looked at this

The vacuum port is connected to the fuel regulator to compensate for engine load. However, if you connect a pressure gauge to the fuel line, the vacuum fluctuations translate to pressure fluctuations. I am sure that BMW have taken this into account, but I thought to see if I can reduce the this and see how it affects the performance.

I've installed a restriction into the line close to the throttle body and thus reduced the pressure fluctuation by 90%+. The restrictor is a tube with a inside diameter of 1mm or less which is about 2-2.5cm long and plugs into the existing vacuum line. Something like Carbtune restrictors.

The effect? the bike seems to be smoother with less vibration on idle and midrange. The pressure is steady and does vary with the vacuum change as it should.

I though that I was kidding myself until I got home from a longish ride to find that the idle has gone up by a few hundred rpm. I assume that I am getting more fuel into the cylinders because of reduced pulsing of the pressure regulator. I need to investigate this, but unfortunately, I will be away next week for the most of it.

Any ideas, comments?

Hi Ned,
A most interesting finding indeed well worth a bit of diagnostic testing on my bike when I get my fuel pressure gauge back from my pal who has it. It will be interesting seeing if my fuel pressure regulator reacts as quickly as yours does.
Regards,
K-BIKE

Ned and K-Bike............You have lost me.

but I will ponder it

Good post though!

Sprocket

Maybe someone can explain it a bit better, I am no word craftsman, but you can see what I am saying by connecting a vacuum gauge to a throttle body (#4) by disconnecting the tube that goes to the fuel pressure regulator.

The reading you will get will be a wild fluctuation between no vacuum and 20 or so. This will be in time with the valves opening and closing.

Now, reconnect the vacuum tube to the fuel regulator and measure the fuel pressure as it idles. The wild fluctuations in pressure will be evident with the pressure gauge flicking in time with the revs.

I asked my self if this is optimal. So, I've placed a restriction in the regulator vacuum like to reduce the fluctuations and found that so long as I don't overdo it with the restriction the fuel pressure becomes steadier and the bike seem to run smoother. This needs a picture, yes?

I grant you that this is a bit esoteric, but it may be a small improvement in running our bikes.

You have a valid point here. I had always assumed that BMW thought the response time of the regulator was "sluggish" so that provided the dampening effect needed. I'll look into this too.

Photos required please Ned.

p.s. I'm sending the $10 back! You certainly don't owe me anything.

blakey wrote:p.s. I'm sending the $10 back! You certainly don't owe me anything.

Very nice to see that we help each others. It's like a big family and we even enjoy the brother in law

Hi all here are a few very grainy videos of my fuel pressure experiments:

1. the first is the standard pressure setup with the vacuum hose connected to throttle body #4. This is at idle and the pressure readings are from the T placed between the pump and the fuel rail
   
   
   
   
2. the second clip is the same setup but with the restriction in the vacuum line. The restrictor is a piece of tubing about 2.5cm long and 1mm ID placed at the throttle body vacuum connector end (Carbtune setup if you have one). This setup allows all the benefits of vacuum fluctuations to vary the fuel pressure at the BMW/Bosch intended, but with less pressure fluctuations :
   
   
   
   
3. This clip shows that the pressure regulator hold the 36psi pressure rock steady when vacuum is removed. I could not see the difference in performance, but I thought that the bike runs smoother with the vacuum disconnected.
   
   
   
   

So there you have it.

Ned, I understand what you do, but when we ride the bikes we run it at far more refs than idle (I know you know ;-)). Normally at the higher refs the fluctuations start to even out. You'll see that when you connect a carbtune or similar and let it idle or cranck it up to 3000 or higher.

It was just an illustration Renez. The bottom line is that I can't tell the difference in performance no matter how it is connected, so I opt for the steady state.

Anyway, I finally got her the way I like my bike to go and feel. It took a lot of replacements of iffy parts and measurements to make sure things are up to spec. For example:

Fuel system

• all rubbers connections to throttle bodies were cracked and suspect so I replaced them
  
• crank case vent tube
  
• all connections leak tested
  
• new pressure regulator
  
• cleaned injectors, one replaced
  
• TPS (throttle off switch) tuned out, full throttle state still in effect
  
• fuel pressure stable, vacuum control taken off
  

That took out buzzing and vibrations.

Ignition:

• about 12 months ago replaced all the leads with "standard" car leads (3000ohms) no problems so far. Still thinking about this.
  

Splines:

• all in a good condition, now well lubed
  

Cooling system

• gone with a good brand name "Green" consistent with the 1980s technology. The PO simply filled the thing with 2.5L of concentrate and added some 0.5L of water. Cooling system internals are spotless.
  
• changed the fan. Good move, this one works great. In traffic the temp drifts between 87 and 93.
  
• thermostat . OEM 85c is ok, but the bike still runs at 75c at speeds above 60km/h. Toyota units work just fine, I will try the 89c after in deep of winter just to see if I can improve the running temperature. I think that the aluminium block is very good at the heat exchange.
  

The long and the short of it is that now I am happy to do some long distance touring.

Ned, ghreat stuff. How did you tackle the vibrations? All in one go or bit by bit? Reason I'm asking is if it was bit by bit what made the most (and the least) difference. Most of us have vibrations we want to tackle, I'm wondering what has the best effects. Some of us have already renewed the rubbers etc, but might not yet have tackled the fuel pressure regulator or the vacuum hose thereof. Can you tell us a bit more?
Cheers, Rene.

PS Was just ripping "Big Pig" to the music server, I have some great memories of your beautiful country!!

ReneZ wrote:Ned, ghreat stuff. How did you tackle the vibrations? All in one go or bit by bit? Reason I'm asking is if it was bit by bit what made the most (and the least) difference. Most of us have vibrations we want to tackle, I'm wondering what has the best effects. Some of us have already renewed the rubbers etc, but might not yet have tackled the fuel pressure regulator or the vacuum hose thereof. Can you tell us a bit more?
Cheers, Rene.

PS Was just ripping "Big Pig" to the music server, I have some great memories of your beautiful country!!

To be honest I didn't set out to solve the vibration thing specifically. I attacked the intake and the ignition systems all at the same time. The byproduct was reduced vibrations. Not totally cured, but no longer prominent or offensive.I did the total intake, including injectors first, changed the plugs and leads second. The biggest improvement was the intake system. Curing the air leaks was the most noticeable improvement.  Oh, and I checked the compression first.Using a spray can with something like WD40 and carefully squirting in all possible places where air can get into the system caused me to take the whole thing apart and renew all rubbers and o rings etc. The rest of the work after that improved things incrementally.The TPS was just an annoyance that affected my riding, a personal thing. The fuel pressure thing just made things nicer. It all seems quieter and smoother. The fuel pressure is s simple suck it and see.The only thing that I am yet to do is valve clearances. As there are no leaks and noises coming from the head end, I will leave it for a bit.Big Pig? wow, it is a distant memory 

Not so distant - I met my wife in Fremantle at the time they were "big". Thanks for the explanation. Maybe I should start exchanging a few more parts and see what it gets me.
Cheers, Rene.

One of the biggest changes with the exchange of fuel pressure regulator is improved starting. It holds pressure for hours and with that it builds pressure instantly the pump starts, the effect of this is almost instant start this morning. It kicked at the first turn and started with a second press of the button and idled without "choke". Normally she will take at least 3 attempts.

There is no magic cure, I don't think. With near 30 yo bikes many bits either fail or a just functioning, so gradual replacement will bear fruit.

Fremantle... know it well. Many hours in Little Creatures with pale ale and Italian sea food on the jetty at the back of the pub ... I'll find the excuse to get there soon

Ned wrote: Fremantle... know it well. Many hours in Little Creatures with pale ale and Italian sea food on the jetty at the back of the pub ... I'll find the excuse to get there soon

Please let us know what is the excuse. We may use it with our better 1/2 too.

Thanks in advance.

Bert

Crazy Frog wrote:

Ned wrote: Fremantle... know it well. Many hours in Little Creatures with pale ale and Italian sea food on the jetty at the back of the pub ... I'll find the excuse to get there soon

Please let us know what is the excuse. We may use it with our better 1/2 too.

Thanks in advance.

Bert

I am old enough to "Do what you wanna do, be what you wanna be" , but even then, she-who-must-be-obeyed comes along and holds her own when it comes to pints of Pale Ale and sea food That is all the excuse I need.

Many attractions in Fremantle, but scantly clad young things, pints of beer and sunset at the back of the pub among the boats of the local fishing fleet has a particular appeal

Right Renez?

The Sail & Anchor with its micro brewery, oh man..............

Probably my last word on this subject, I promise
After reading your comments re: sacrilegious acts of modifying the sacred K100 and Bosch L-Jet , I thought now that I have a new regulator, I should connect the vacuum back and see how it all goes.

Rode to work with with the vac connected and let me tell you, I couldn't wait to disconnect the thing.

What happened, I hear you ask...well the bike got the buzz back through all the gears and revs. Not alarming, but simply noticeable and annoying.

So, when i got rid of it and the bike went back to her sweet self on my way home.

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BTW the benefit of a new regulator is great starting... the bike now starts from cold in the morning on a first press of the button even without the "choke"!

It used to take me three goes before she would kick. The explanation is obvious.. I finally get the correct amount of fuel on start and don't have to wait for the pump to build up the pressure through a leaky regulator.

Good article. They won't run factory spec forever but will run forever if massaged.
This seemed more a massage than a rip it & change it.

walker