BMW K bikes (Bricks)

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V11POW

V11POW
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Hello from Christchurch, Dorset.
My sprag clutch was stuck so I followed the excellent posts on here to free it off using Seafoam sprayed into the three holes.
I used 5th gear to rotate the crank manually via rear wheel.

After a couple of days of heating and spraying the engine turned again on the button.
Oil back in, plugs cleaned and connected. The motor fired on the button, but was running very erratically. It picks up okay on the throttle but dies pretty quickly on no throttle.
I tried opening the tank cap - no difference.
Re-checked the plugs. All okay..


I rode it into the garage before the sprag issue, so it was running perfectly well for a 90,000 miler.

What on earth have I done by freeing the sprag?

Thanks for reading this far..
Neil.

    

Arlina

Arlina
Moderator
Moderator
Just for the record, does the pump run?


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Sprag clutch fixed... engine starts but is sick.. what have I done? Eu-log10  K1100RS/LT - R1200RT - R1100RS (RIP) - Cagiva SST 350 Ala Verde - K75LT project
    

V11POW

V11POW
active member
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@Arlina wrote:Just for the record, does the pump run?
Yes.
Everything 'sounds' normal. 
The motor fires first spin, but has the feel of an over choked engine. However, the K's 'choke' is operating correctly.
And I haven't touched anything on that side of the block.

Neil.

    

Point-Seven-five

Point-Seven-five
Life time member
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You may have disturbed the infamous Z tube during your ministration to the sprag. I would advise to look closely at it for cracks.


__________________________________________________
Present:
1994 K75RT
1991 K100RS
1988 K100RS SE

Past:
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

Laitch

Laitch
Life time member
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If the oil filler cap O-ring isn't sealing, that could affect idling, too.


__________________________________________________
1995 K75 81,000 miles
Sprag clutch fixed... engine starts but is sick.. what have I done? Usa-lo10
    

V11POW

V11POW
active member
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Thank you everyone..

I have checked the oil filler plug for sealing. (I once rode off to Silverstone having left the cap on the shelf next to the oil can. Having discovered this I had to fashion a temporary filler cap out of garbage - but it worked - lesson learnt)

"the infamous Z tube' - Is this the short rubber tube visible just above the manifold to the airbag? That did look okay.

My fear was damaging something by bumping the engine back as well as forward via the rear wheel to get to the sprag holes.


I've had another poke at it tonight.
The temperature in the garage is 4 deg C
The bike starts on the button with no choke from cold, and does idle (just) at about 600rpm. As soon as I wind the choke lever round the engine dies. This would obviously lift the idle speed but its just kills it.

Thanks for your thoughts so far...

    

Dai

Dai
Life time member
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- Stand by the left side of the engine
- Crouch down next to the rearmost cylinder
- Look just above it and slightly towards the coils cover

There's a tube that connects the plenum chamber (the plastic box on top of the throttlebodies) to the crankcase. That's the 'infamous z-tube'. They are very prone to cracking where they exit the plenum chamber and the result is pretty much what you are experiencing.

'V11POW' - I guess you're a Guzzi owner too?


__________________________________________________
1983 K100 upgraded to K100RS spec, 1987 K100RT
Others...
1978 Moto Guzzi 850-T3, 1979 Moto Guzzi 850-T3 California,1993 Moto Guzzi 1100ie California
2020 Royal Enfield Bullet 500
    

Point-Seven-five

Point-Seven-five
Life time member
Life time member
The cracks form near the hose clamps. You have to look close because they are small, but still mess up the running of the engine.

While you're looking for air leaks, check the caps that cover the vacuum ports on the throttle bodies. Besides the "infamous" Z tube, these are among the items that knowledgeable brick riders replace when getting a "new" bike. At 30 years of age, if they haven't started leaking yet, they are likely to start fairly soon, and at the most inopportune time.


__________________________________________________
Present:
1994 K75RT
1991 K100RS
1988 K100RS SE

Past:
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

92KK 84WW Olaf

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Just to add....same thread, there is also a vacuum line from the throttle bodies near that Z tube that loops around to the fuel pressure regulator. This may have a spring around t for protection but its easily damaged.

Vacuum caps also.

And....on early Ks there is another vacuum pipe at he front of the throttle bodies near No 1 that also loops around to a vacuum sensor.

On the Z pipe, a quick test if you get ending running...remove the oil filler cap = makes no difference means the Z pipe is KO

Loss of vacuum on the other pipes/caps means the fuel pressure regulator gets no vacuum = over pressure = over fuelling.


__________________________________________________
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 0011171 Fricka 606 Alaska Blue 29,495 miles Damn K Pox Its a Bat outta Hell Now 37,190 miles
1996 K1100LT 0233004 Lohengrin Mystic Red 38,000 miles.
    

V11POW

V11POW
active member
active member
@Dai wrote:- Stand by the left side of the engine
- Crouch down next to the rearmost cylinder
- Look just above it and slightly towards the coils cover

There's a tube that connects the plenum chamber (the plastic box on top of the throttlebodies) to the crankcase. That's the 'infamous z-tube'. They are very prone to cracking where they exit the plenum chamber and the result is pretty much what you are experiencing.

'V11POW' - I guess you're a Guzzi owner too?
Had a couple of V2 Ducatis once..
Thanks for the description. I renewed that tube a few years back when I also did the manifold rubbers and vacuum caps. I'm hoping these are still okay as they aren't the originals.

I am continuing to ponder this little challenge..

Thanks everyone for the other thoughts..

I will post a response/ solution when I find the culprit. Sprag clutch working fine now though..

Best Regards
Neil.

    

Holister

Holister
Life time member
Life time member
Definitely sounds like an air leak. Check the air filter is seated and clips are properly fastened.
Sea Foam is pretty rugged so you might've even developed some air leaks around the valve and crank cover seals or even the cover bolt seals.
Spray some brake cleaner or similar around the throttle bodies, Z-tube, air filter, etc etc and listen for an increase in running.
Check your spark plugs after it stalls. That will tell you a lot about what's happening with the fuel and air.

You need to flush that Sea Foam out really well. I reckon you'd need 2 or 3 oil flushes before that and all the sludge is properly gone.


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1989 K100RT     VIN  0097367 (naked)  
1996 K1100RS   VIN  0451808
  Sprag clutch fixed... engine starts but is sick.. what have I done? Austra12    Fuel:  95 Octane
Engine Oil: Nulon Full Synthetic 15W50
Gear Box Oil:  Nulon Synthetic 75W90
    

moriarti

moriarti
Life time member
Life time member
Hi Neil,Ifind the best way to REALY flush the engine is to drain oil when engine is hot,then fill to max mark with diesel fuel,remove spark plugs,spin engine for 10/15 seconds,wait a minute to protect starter and repeat a few times to ensure diesel has reached all parts leave for a few hours.Drain fit new filter fill with new oil.You will be gobsmaked at the crap this method removes.Worked for me on a lot of engines over the years.JUST DON'T fire it up with the diesel in affraid


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1984 k100 rs red/black VIN  0004449
    

Corkboy

Corkboy
Life time member
Life time member
Just to pipe in as well,

I had similar problems.  When the bike was idling I sprayed brake cleaner (or other combustable arosol) around the area of the injectors/ z tube. If the idle picks up - it's an air leak. As said, check rubbers.  I found tiny cracks in the z tube - replacement solved the problem.

The "choke" only increases the idle slightly, it does nothing to fueling/air mixture.


__________________________________________________
Regards,

Corkboy '87 K100RS SE (The black one - one of the two bikes I'm sorry I sold)
             '87 K100RS 0140995 (Gone)
             '97 K1100LT 0188024 (Gone)
             '08 K1200GT Wedge - but still a K
             '08 Transalp 700
    

V11POW

V11POW
active member
active member
Thanks for the input everyone..

I'm am re-checking the crank case cover seal and bolt seals as oil is appearing where it didn't used to..
I have the mercury tubes connected and the levels are all over the place - so I clearly have work to do.
Air filter was located correctly, but I will order new. Had the bike running last night and it kept going better, but lumpy, long enough for the fan to kick in. So that's a plus..
I've always had an odd vacuum reading on Cyl 4 so I'm going to find out what's going on there too...

I was always planning on a major strip down at 100,000 miles, but it looks like I'm doing it at 90,000 instead..

Thanks again.. 
Go safely..

    

92KK 84WW Olaf

avatar
Life time member
Life time member
Odd vacuum if too low on no 4 points to the vacuum pipe to the fuel pressure regulator being split.


__________________________________________________
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 0011171 Fricka 606 Alaska Blue 29,495 miles Damn K Pox Its a Bat outta Hell Now 37,190 miles
1996 K1100LT 0233004 Lohengrin Mystic Red 38,000 miles.
    

Point-Seven-five

Point-Seven-five
Life time member
Life time member
Vacuum levels all over the place...

A low vacuum that doesn't match the others indicates an air leak on that throttle body. Might give you a clue as to where you need to be checking the rubber bits for cracks and/or bad sealing.


__________________________________________________
Present:
1994 K75RT
1991 K100RS
1988 K100RS SE

Past:
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

17Back to top Go down   Sprag clutch fixed... engine starts but is sick.. what have I done? Empty Chasing air leaks on Wed Nov 25, 2020 2:16 pm

V11POW

V11POW
active member
active member
Hmm, I replaced the manifold and throttle body rubbers, and the Z pipe about 8 years ago. 
Looks like I'm doing it again..
All the best..
Neil.

    

Point-Seven-five

Point-Seven-five
Life time member
Life time member
For what it costs, I think I would replace an 8 year old Z-tube just to be sure that isn't the problem. If the old one turns out to be good, you can hang on to it as a spare.

I know I had one give me fits when it had an almost invisible crack that I could only see when the tube was off the bike. Right by the hose clamp at the airbox end of the tube.


__________________________________________________
Present:
1994 K75RT
1991 K100RS
1988 K100RS SE

Past:
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

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