BMW K bikes (Bricks)


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sidecar paul

sidecar paul
Life time member
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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.


__________________________________________________
'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

Kyle10
Life time member
Life time member
Glad to hear it, Paul. Did you use an OEM replacement?


__________________________________________________
1985 K100rt 0052183
1983 Honda VF750 007713 
    

sidecar paul

sidecar paul
Life time member
Life time member
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.


__________________________________________________
'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

Kyle10
Life time member
Life time member
Just saw it. Love to find a US counterpart for that price.


__________________________________________________
1985 K100rt 0052183
1983 Honda VF750 007713 
    

Two Wheels Better

Two Wheels Better
Moderator
Moderator
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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"A long ride is the answer to a question you will soon forget!" ~ Anonymous
1977 R75/7-100, '93 K11/K12 Big Block, '93 K1100RS, '95 R100 Mystic, '96 K1100RS, 2 x '98 K1200RS, '06 K1200R & '09 K1300GT
    

Arlina

Arlina
Moderator
Moderator
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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Thank you FORUM. Problem solved; and I didn't even need to ask the question! Eu-log10  K1100RS/LT - R1200RT - R1100RS - Cagiva SST 350 Ala Verde - K75LT project - K75 Schurgers - K75S - K1100RS - K75RT - K75C
    

Kyle10

Kyle10
Life time member
Life time member
Two Wheels Better wrote:Enter Here Then Scroll Down
Thanks TWB. EME's a great shop, too.


__________________________________________________
1985 K100rt 0052183
1983 Honda VF750 007713 
    

charlie99

charlie99
VIP
VIP
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


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

'86 K100 RT..#0090401 ..."Gerty" ( Gertrude Von Clickandshift ) --------O%O
'86 k100 rs.. #######..  "Fred " (f(rame) red ) ( Fredrick leichtundschnell ) - -
bits and pieces from many kind friends across the k100 world ...with many thanks ..
1987 k100rs ########   "Red"  - (red sports rs TWB style )
1989 K100rt #009637   "Black Betty"  (naked rt ala Nigel , now sporting an rs main fairing )
    

mike d

avatar
Life time member
Life time member
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!  Thank you FORUM. Problem solved; and I didn't even need to ask the question! Affraid 

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

ReneZ
Life time member
Life time member
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 Australia! Having a 'new' K     Surprised-o: 

Rene


BMW K100 - 1985 (0030029) Scotland Thank you FORUM. Problem solved; and I didn't even need to ask the question! Rain
BMW K1200GT - 2003 (ZK01223) Florida
BMW K1200GT - 2004 (ZK27240) Australia
    

sidecar paul

sidecar paul
Life time member
Life time member
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

88
Life time member
Life time member
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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Thank you FORUM. Problem solved; and I didn't even need to ask the question! Ir-log1188....May contain nuts!Thank you FORUM. Problem solved; and I didn't even need to ask the question! Ir-log11

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

K1 - 1989 - AKA Titan (unique K1/K1100RS hybrid by Andreas Esterhammer)
K1100RS - 1995. AKA Rudolf Von Schmurf (in a million bits)
K100RS - 1991 AKA Ronnie. Cafe racer project bike
K75RTP - 1994
K75C - 1991 AKA Jim Beam. In boxes. 
K1100LT 1992 - AKA Big Red (gone)
K100LT - 1988 - AKA the Bullion brick. Should never have sold it.
    

ReneZ

ReneZ
Life time member
Life time member
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.


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

Rene


BMW K100 - 1985 (0030029) Scotland Thank you FORUM. Problem solved; and I didn't even need to ask the question! Rain
BMW K1200GT - 2003 (ZK01223) Florida
BMW K1200GT - 2004 (ZK27240) Australia
    

Kyle10

Kyle10
Life time member
Life time member
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.


__________________________________________________
1985 K100rt 0052183
1983 Honda VF750 007713 
    

sidecar paul

sidecar paul
Life time member
Life time member
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.

Thank you FORUM. Problem solved; and I didn't even need to ask the question! Sam_0918

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!

Thank you FORUM. Problem solved; and I didn't even need to ask the question! Sam_0919

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

charlie99
VIP
VIP
wouldn't be the first time we have seen intermittency on the failure  paul

interesting to see the internals

cheers


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

'86 K100 RT..#0090401 ..."Gerty" ( Gertrude Von Clickandshift ) --------O%O
'86 k100 rs.. #######..  "Fred " (f(rame) red ) ( Fredrick leichtundschnell ) - -
bits and pieces from many kind friends across the k100 world ...with many thanks ..
1987 k100rs ########   "Red"  - (red sports rs TWB style )
1989 K100rt #009637   "Black Betty"  (naked rt ala Nigel , now sporting an rs main fairing )
    

ReneZ

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


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

Rene


BMW K100 - 1985 (0030029) Scotland Thank you FORUM. Problem solved; and I didn't even need to ask the question! Rain
BMW K1200GT - 2003 (ZK01223) Florida
BMW K1200GT - 2004 (ZK27240) Australia
    

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