BMW K bikes (Bricks)

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sidecar paul

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Let me explain:

The outfit hasn't been running too sweetly of late, getting progressively worse. Rough at low engine speeds but seemingly OK above 
3000 rpm.

I suspected the AFM, maybe a sticking flap, but changing it made no difference. scratch

Last Friday I realised that it was running very rich and, remembering posts about this topic, I used the search facility to find references to 'RICH MIXTURE'.

A good read came up with many ideas, but Krambo's thread seemed to match my problem perfectly, with the following suggestions.

So, 3 possibilities, fuel pump, fuel pressure regulator or a blockage in the return feed to the tank.

Using Bert's (Crazy Frog) excellent 'Trouble Shooting Guide', I connected a pressure gauge to the fuel rail via a tee piece......WOW pressure off the scale!  affraid

Next, check the pressure coming from the fuel pump........again off the scale. I used the tank off the solo to confirm that the FPR was still functioning correctly and hadn't suffered from the excessive pressure. Yes, we all need at least 2 K's cheers  

The conclusion was, therefore, a duff pressure relief valve in the fuel pump.

Today the new pump arrived and, after resetting the bypass screws (I had tried to get a decent tickover with the fault, so they were way out), all is back to normal.  roundel

So, you see, without this FORUM I, and probably many others, would be struggling to keep my bikes running.

Hence a big THANK YOU!


Paul.


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'84 K100RS (0014643) (owned since '85), 86 K100RS (0018891) with Martello sidecar (built as an outfit in '88),
'51 Vincent (since '67),'72 Montesa Cota (from new), '87 Honda RS125R NF4 (bought 2015) 
....No CARS never ever!
    

Kyle10

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Glad to hear it, Paul. Did you use an OEM replacement?


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1985 K100rt 0052183
1983 Honda VF750 007713 
    

sidecar paul

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No, Kyle, I put the substitute pump in a separate thread so that it will be easier for anyone to find at a later date.

Paul.


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'84 K100RS (0014643) (owned since '85), 86 K100RS (0018891) with Martello sidecar (built as an outfit in '88),
'51 Vincent (since '67),'72 Montesa Cota (from new), '87 Honda RS125R NF4 (bought 2015) 
....No CARS never ever!
    

Kyle10

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Just saw it. Love to find a US counterpart for that price.


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1985 K100rt 0052183
1983 Honda VF750 007713 
    

Two Wheels Better

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That's a good price (referring to the eBay link on the other post)! In the USA, check EME's price on a new Enduralast fuel pump. With the exchange rate from Pounds to USD from the eBay site, £48.95 plus £22.00 postage = £71.00, that's equivalent (today) to USD$111. EME has one for $129 plus postage or $112 for a replacement 'kit' which includes ancillaries. And no extra waiting for the Royal Mail parcel to arrive at your door from the UK. The deals are out there if one knows where to look.

Enter Here Then Scroll Down


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'77 R75/7-1000cc, '87 K100RS, '93 K12 Big Block, '94 R100 Mystic, '03 K1200GT, '04 R1150RT, '06 K1200R, '07 K1200R & '09 K1300GT
    

Wheeldigger

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@sidecar paul wrote:
The conclusion was, therefore, a duff pressure relief valve in the fuel pump.
You just give me a wonderful idea :BW:
Never thought of that, got 2 K75 with fuelproblems.
(What "we all must have at least 2 K's".....)
Heaters up, shedman is coming Smile


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07/1987 K569 K 75 S (0563,0572) USA
    

Kyle10

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Thanks TWB. EME's a great shop, too.


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1985 K100rt 0052183
1983 Honda VF750 007713 
    

charlie99

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great solve paul

would never have thought of that, without the forum

cheers and great news that contributions have rewarded in a solve ...yet again ...

cheers from down here


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cheezy grin whilst riding, kinda bloke ....oh the joy !!!! ...... ( brick aviator )

'86 K100 RT..#0090401 ..."Gerty" ( Gertrude Von Clickandshift ) --------O%O
    

mike d


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Paul,

Using Bert's (Crazy Frog) excellent 'Trouble Shooting Guide', I connected a pressure gauge to the fuel rail via a tee piece......WOW pressure off the scale!   

Was that where you would have expected 32 psi? If so would that not point to the regulator not dumping the excess back to the tank?

Mike

    

ReneZ

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No, its indicating that the fuel pressure regulator doesn't allow any fuel to return to the tank. Therefore you'll be seeing the max pressure the pump can generate until its build-in safety blows Very Happy


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Greetings from Florida! Having a 'new' K  :cyclops:    Surprised-o: 

Rene


BMW K100 - 1985 (0030029)
BMW K1200GT - 2003 (ZK01223)
    

sidecar paul

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Mike, as I see it, the pressure at the fuel rail should be maintained at 36 PSI by the FPR, with the pump supplying at 65 PSI, so a
 tee-piece to a pressure gauge from the fuel rail should read 36 PSI.

 Now, if the pump pressure relief valve isn't working and the pump is supplying around 160 PSI, the FPR can't allow enough fuel to pass to reduce the fuel rail pressure to the required 36 PSI, hence the high pressure reading.

Paul.


__________________________________________________
'84 K100RS (0014643) (owned since '85), 86 K100RS (0018891) with Martello sidecar (built as an outfit in '88),
'51 Vincent (since '67),'72 Montesa Cota (from new), '87 Honda RS125R NF4 (bought 2015) 
....No CARS never ever!
    

88

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This forum is getting to be a great database on knowledge thanks to people like you who post their findings. Well done, nice result!


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88....May contain nuts!

"The world is a book and those who do not travel read only one page." - St. Augustine from 1600 years ago & still true!

Bike: K100LT 1988. 0172363. AKA the Bullion Brick! Mods: k1100 screen and stands.
K1: 1990. 6374189. Custom Stealth Black paint.
    

ReneZ

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Team, there's a difference between pressure and delivery volume with a pump. I doubt that the pump can bring up enough pressure at volume if the FPR is fully open.


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Greetings from Florida! Having a 'new' K  :cyclops:    Surprised-o: 

Rene


BMW K100 - 1985 (0030029)
BMW K1200GT - 2003 (ZK01223)
    

Kyle10

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@ReneZ wrote:Team, there's a difference between pressure and delivery volume with a pump. I doubt that the pump can bring up enough pressure at volume if the FPR is fully open.
Thank you, Rene. Getting a bit confuzzled there...

Opinion please. I've installed 4-hole injectors. Love them. After reading thru the posting re pressure levels for 2-hole vs. 4-hole and the possible drop in injector efficiency (Thanks Capt. Hollister) I am considering an aftermarket adjustable FPR (ref. this) to dial in a bit more pressure for the 4-holers. 

Thanks in advance.


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1985 K100rt 0052183
1983 Honda VF750 007713 
    

sidecar paul

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It seems that I was a bit premature with my report of success as, on the first ride, the richness reappeared after a short distance. Returning home I found that I was still getting an excess pressure at the fuel rail.  Embarassed

The only other item in the chain is the fuel pressure regulator, so I bought and fitted a new one and, bingo, after a short 30 mile hop last night things are now really back to normal. cheers

On reflection, considering some of my hasty conclusions, I can't see how a simple spring loaded pressure relief valve on the fuel pump could fail, but I did see a high reading on the pressure gauge when connected to the output. Anyway, a new fuel pump after 28 years use is probably no bad thing. 

Last night, discussing all this with a friend who used to work with fuel systems, he said he was surprised that a Bosch FPR, being quite a simple bit of kit, could fail causing a blockage. The more likely failures would leave a free flow or, with a ruptured diaphragm, dumping fuel into the manifold via the vacuum hose. So he urged me to take the old one apart.

This morning I turned off the flange and here's what's inside a FPR.



That flat valve should be captive in it's housing, but with wear on the ball and on the plate that holds it in place, it was able to escape!



So, it would seem that the diaphragm was moving backwards under fuel pressure but leaving the valve behind to block the output port.

Well, at least I now know what's inside a FPR and in spite of a few blind alleys, I've got to the bottom of the problem.

I suppose a modern engine would probably have a sensor on the fuel rail which would shut down the 'computer' when over pressure is detected requiring a visit to your dealer! It's a tribute to the K design that it still runs with such a fault which makes it possible to (eventually) diagnose.

Paul.


__________________________________________________
'84 K100RS (0014643) (owned since '85), 86 K100RS (0018891) with Martello sidecar (built as an outfit in '88),
'51 Vincent (since '67),'72 Montesa Cota (from new), '87 Honda RS125R NF4 (bought 2015) 
....No CARS never ever!
    

charlie99

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wouldn't be the first time we have seen intermittency on the failure  paul

interesting to see the internals

cheers


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cheezy grin whilst riding, kinda bloke ....oh the joy !!!! ...... ( brick aviator )

'86 K100 RT..#0090401 ..."Gerty" ( Gertrude Von Clickandshift ) --------O%O
    

ReneZ

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Good one and thanks for posting the pictures, good knowing how it looks like and what possible fails might come from it!


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Greetings from Florida! Having a 'new' K  :cyclops:    Surprised-o: 

Rene


BMW K100 - 1985 (0030029)
BMW K1200GT - 2003 (ZK01223)
    

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