BMW K bikes (Bricks)

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skidz449

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I've had this bike (1985 K100RS) for a month or so and it has performed beautifully til last week. The bike starts and runs smoothly at all speeds if I open the the throttle in moderation. But this past week in passing situations, or if I just want to feel the thrill and thrust of this 4 cylinder machine, I quickly open the throttle to the full on position and the motor craps out and jerks like it is running out of gas. Roll the throttle back and it runs fine again and will smoothly accelerate to 6000 RPM if I'm gentle with the throttle.
Feels as though the fuel supply can't keep up with the instant demand. So far I have changed the fuel filter, air cleaner, spark plugs, cleaned the injectors, run another tank of fuel (with injector cleaner). No change.
I live in Nicaragua now and I would be willing to bet that I own the only bike of this kind in the entire country! Parts may be hard to come by, but I have found a shop with some diagnostic equipment that is willing to help, he is a Mercedes mechanic with very little motorcycle experience. They sell Chinese made 150cc machines here by the boatload, but big bikes are very rare and very expensive, so I was really happy to find this beauty at a price I could afford. I have been riding and maintaining carburated V-twins for more than 20 years, but this is my first fuel injected bike, so I'm a little out of my depth. Any ideas on the most likely item to check, test, or change next will be appreciated.

    

92KK 84WW Olaf

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There are no diagnostic sockets on the K100 you have.

Maybe go to the Portal tab and go to what to do if you have just bought a K bike.

It seems you have done the essential things like fluids etc. If the Mercedes mechanic has the means you could test the injectors, since Bosch make the Mercedes injectors and most of them are fuel injected he may have something available.

If you have some carb cleaner spray it around the throttle bodies with the engine running. If the engine changes it means its being sucked in through leaks on the intake side, that will cause problems. Some rubber parts perish with age and others go hard and crack.



Last edited by 92KK 84WW Olaf on Thu Jul 20, 2017 11:39 am; edited 1 time in total


__________________________________________________
1992 K100LT 0193214 Alaska Blue 101,000 miles
1984 K100RT 0022575 Baja Red bought 36,000 now 89,150 miles
1997 K1100LT 0188024 Mystic Red 58,645 now 74,700 miles
    

3Back to top Go down    Nicaraguan K bike on Thu Jul 20, 2017 11:20 am

skidz449

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Good idea, carb cleaner is cheap and might tell me something. The rubbers on the throttle body look OK, but let's see what happens.

    

Snod Blatter

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Not firing at full throttle can also be a symptom of poor spark, either due to dead plugs or HT leads. Start with the simple stuff!


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1989 K100RS SE ABS 8v VIN: 0149214
Others: 1.5 x Honda CBX250RS-E, '94 CB250, '95 TRX850, '16 Z250SL
http://justbikethings.blogspot.co.uk/
    

Holister

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@skidz449 wrote:
...... I quickly open the throttle to the full on position and the motor craps out and jerks like it is running out of gas. Roll the throttle back and it runs fine again and will smoothly accelerate to 6000 RPM if I'm gentle with the throttle.......
There's a switch on the TPS for wide open throttle (WOT). It signals the FICU to richen the mix for hard acceleration. You'll need to use a DMM to check its working properly.... 12v at pin FICU #3 (count pins from the lead end of the plug).

Also a possibility is that your MAF is crapping out.


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1988 K100RT VIN No. 0094680
1989 K100RT VIN No. 0097367 (naked)
1996 K1100RS VIN No. 0451808
Fuel: 95 Octane
Engine Oil:Nulon Full Synthetic 15W50
Gear Box Oil: Nulon Synthetic 75W90
    

6Back to top Go down    1985 K100 Full throttle bog down on Sun Jul 23, 2017 5:32 pm

skidz449

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Thanks for the input Hollister. Your comment led me to the TPS, I could detect no click from the unit when moving the throttle and no ohm values across the terminals in any position. I removed the unit only to find that when I put it face up on the bench and came back to it a few minutes later, that it was sitting in a puddle of oil..??? I wiped it off and set it back on the bench and in a short time a new sploog of oil had again materialized under the TSP. Probably no more than a teaspoon of oil, but I can't imagine where it came from, and I'm certain that this electronic switch will not benefit from being oiled so well. Still, I did the reccomended tests across the terminals with an ohm meter again, and found no resistance in any throttle position.
The bike runs the same without the TPS in place, in that it accelerates smoothly if I am gentle, but craps out completely in the WOT position. Nicaragua has only 2 lane roads, so I need that WOT position to work when passing
The same TPS unit has been used on lots of BMW cars and bikes, so I'll buy a new one tomorrow and see if that will solve my problem.

Skidz449
1985 K100RS

    

MartinW

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Bricks seem to benefit from running a couple of bottles of Caltex Techron through them. Half a bottle per tank consecutively. After running the two bottles initially one bottle a year seems to be fine.
Regards Martin.

    

Holister

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Well it could be your injectors. But i'd take them out, clean them and replace the kit (o-rings etc)
Also check your fuel pressures. about 60psi from the pump. 36psi at the fuel rail. FPR may be faulty. A slight drop in rail pressure may only show up at peak demand (WOT).


__________________________________________________
1988 K100RT VIN No. 0094680
1989 K100RT VIN No. 0097367 (naked)
1996 K1100RS VIN No. 0451808
Fuel: 95 Octane
Engine Oil:Nulon Full Synthetic 15W50
Gear Box Oil: Nulon Synthetic 75W90
    

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