BMW K bikes (Bricks)


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Swedish.brick

Swedish.brick
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Hello fellow K riders,

I am having trouble with my 84 K100 RS not running properly. It starts and runs but very rough and blurry. Theres also backfiring from the exhaust, even when idling.

The spark plugs looks pretty sooty/oily. And you can tell that they are a little wet. I have ordered new ones tho, because when i checked the spark quality one or two of them looked pretty weak, even though they are almost brand new. The bike have been sitting for a year since it last ran. But then it was running just fine.

I also checked the leads and they look ok. I dont suspect the coils because i had them replaced last year due to errors on the old ones. They are second hand tho.

Pulled the fuel rail to see if the injectors were working ( also new ) and they did.

Anyhow, when testing to see if i had the correct fuel pressure it looked like this ( see video ) If you look closely you can see that it spikes up to 50psi, sometimes 60. And when i increase the rpm, the pressure also increases. Is it supposed to be like that?

When i turn the ignition off, it stays on about 36 psi as it should. At least for an hour or so. Could it be a faulty fuel pressure regulator?

Any input appriciated!


    

92KK 84WW Olaf

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Check your vacuum lines and vacuum caps first.

Just beside your throttle position sensor at no 4 there is a vacuum line, the original one has a spring on it, it goes to the fuel pressure regulator. If this line is cracked it will cause the fuel pressure regulator to not work and give you excessively high fuel pressure as you have found.

Those vacuum pipes and caps and Z pipe should be replaced max 5 years in my book.


__________________________________________________
1992 K100LT 0193214 Bertha Blue 101,000 miles
1984 K100RT 0022575 Brutus Baja Red 578 bought 36,000 now 89,150 miles
1997 K1100LT 0188024 Wotan Mystic Red 689 58,645 now 106,950 miles Deceased.
1983 K100RS 0011157 Fricka 606 Alaska Blue 29,495 miles Damn K Pox Its a Bat outta Hell Now 58,200 miles. 
1996 K1100LT 0233004 Lohengrin Mystic Red 38,000 miles currently 49,200 miles.
1983 K100RS 0004449 Odette R100 colours 58,000 miles. Sprint fairing now 63,390 miles

Past:
1968 Yamaha 80 YG1
1971 Yamaha 125 YAS-1
1968 Honda 125 SS
1970 Honda CD 175
1973 Honda CB500-4
Honda CX 500
    

Swedish.brick

Swedish.brick
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Thanks for the tip, I have replaced all the vacuum lines and caps with new ones. And ther is no kinks anywhere that i can see.

But you do agree that its something wrong with the pressure?


__________________________________________________
BMW K100RS -84
    

92KK 84WW Olaf

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Swedish.brick wrote:Thanks for the tip, I have replaced all the vacuum lines and caps with new ones. And ther is no kinks anywhere that i can see.

But you do agree that its something wrong with the pressure?

It does sound like it and I am actually replacing the FPR on one of my Ks for this reason. I have had a few go faulty over the years.

There is a diaphragm inside it that can go wrong, age, etc etc. Its worth checking to see if you find any petrol in the vacuum line at no 4- perforated diaphragm if you do. It will suck extra fuel into no 4 and seriously enrich 1 2 and 3.


__________________________________________________
1992 K100LT 0193214 Bertha Blue 101,000 miles
1984 K100RT 0022575 Brutus Baja Red 578 bought 36,000 now 89,150 miles
1997 K1100LT 0188024 Wotan Mystic Red 689 58,645 now 106,950 miles Deceased.
1983 K100RS 0011157 Fricka 606 Alaska Blue 29,495 miles Damn K Pox Its a Bat outta Hell Now 58,200 miles. 
1996 K1100LT 0233004 Lohengrin Mystic Red 38,000 miles currently 49,200 miles.
1983 K100RS 0004449 Odette R100 colours 58,000 miles. Sprint fairing now 63,390 miles

Past:
1968 Yamaha 80 YG1
1971 Yamaha 125 YAS-1
1968 Honda 125 SS
1970 Honda CD 175
1973 Honda CB500-4
Honda CX 500
    

Point-Seven-five

Point-Seven-five
Life time member
Life time member
Remove the return line to the tank an route it into a bottle.  Start the engine and check the fuel pressure. 

I suspect that you may have a stuck or blocked check valve in the spigot where the return line connects to the tank.  It will restrict the flow from the fuel pressure regulator to the tank forcing the pump to it's maximum output pressure which is approximately 60-65 psi.


__________________________________________________
Present: 1991 K100RS "Moby Brick Too"
 
Past:
1994 K75RT "Ilsa, She Wolf of the SS"
1988 K100RS SE "Special Ed"
1994 K75S "Cheetos"
1992 K100RS "Moby Brick" R.I.P.
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

charlie99

charlie99
VIP
VIP
Looks about right 2.2 to 2.5 bar 

You could tske the vacuume line off and see what it is ... perhaps 2.5 bar c or higher constant 

Rel issues are when its below 2 bar


__________________________________________________
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 )
    

Swedish.brick

Swedish.brick
active member
active member
Point-Seven-five wrote:Remove the return line to the tank an route it into a bottle.  Start the engine and check the fuel pressure. 

I suspect that you may have a stuck or blocked check valve in the spigot where the return line connects to the tank.  It will restrict the flow from the fuel pressure regulator to the tank forcing the pump to it's maximum output pressure which is approximately 60-65 psi.

That’s a good suggestion, I’ll try that and see what happens!

    

slowandlow

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And be sure to use only Bosch X5DC spark plugs, NGK will not work.

    

Laitch

Laitch
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slowandlow wrote:And be sure to use only Bosch X5DC spark plugs, NGK will not work.
NGK plugs of the same relative type should work if they have terminal nuts installed on them.


__________________________________________________
1995 K75 90,000 miles
    

Swedish.brick

Swedish.brick
active member
active member
Laitch wrote:
slowandlow wrote:And be sure to use only Bosch X5DC spark plugs, NGK will not work.
NGK plugs of the same relative type should work if they have terminal nuts installed on them.

That’s right. I use NGK D7EA with the terminal nuts. Worked just fine last year.

    

slowandlow

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I tried NGK years ago, they went charcoal black almost at once, went for Bosch instead, they lasted 10 years without problems. Someone here wrote it has to do with internal resistance: the Bosch plugs are adapted to the Beru original ignition cables/ caps, the NGK are not. I guess you have to try, if NGK works then its fine, if they goe black then try Bosch instead.

    

92KK 84WW Olaf

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Also make sure that whatever plug you use, it must not have an R in the code. R codes are for the 16v engines.


__________________________________________________
1992 K100LT 0193214 Bertha Blue 101,000 miles
1984 K100RT 0022575 Brutus Baja Red 578 bought 36,000 now 89,150 miles
1997 K1100LT 0188024 Wotan Mystic Red 689 58,645 now 106,950 miles Deceased.
1983 K100RS 0011157 Fricka 606 Alaska Blue 29,495 miles Damn K Pox Its a Bat outta Hell Now 58,200 miles. 
1996 K1100LT 0233004 Lohengrin Mystic Red 38,000 miles currently 49,200 miles.
1983 K100RS 0004449 Odette R100 colours 58,000 miles. Sprint fairing now 63,390 miles

Past:
1968 Yamaha 80 YG1
1971 Yamaha 125 YAS-1
1968 Honda 125 SS
1970 Honda CD 175
1973 Honda CB500-4
Honda CX 500
    

Swedish.brick

Swedish.brick
active member
active member
A little update,

As suggested above I bypassed the fuel return valve in the tank with an extended hose from the fuel pressure regulator directly back in the tank through the fuel cap.

This did the trick! The pressure is much more stable and doesn’t spike or increase with the rpm. 

I removed the return valve from the tank, but was confused when there was nothing blocking it inside. But, when I blew through the hole to see if there was any resistance, there was a pressure build up inside the tank! (Fuel cap was shut)

The blockage was actually in the ventilation that goes from the top of the tank and out on the bottom through a small hose. This resulted in a pressurized tank and not letting the fuel flow normally back to the tank.



Last edited by Swedish.brick on Thu Jun 13, 2024 2:30 pm; edited 1 time in total

    

Dai

Dai
Life time member
Life time member
Ah. I've seen that happen in one tank and it was a bugger to unblock (I think it was Brick 2's tank). I got there eventually.


__________________________________________________
1983 K100 naked upgraded to K100LT spec after spending time as an RS and an RT
1987 K100RT
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