BMW K bikes (Bricks)

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1Back to top Go down   Low RPM Low Power Jerky Acceleration Empty Low RPM Low Power Jerky Acceleration on Tue Aug 11, 2020 9:26 pm

Ohnij

Ohnij
active member
active member
Looks like a number of folks here have had similar issues as mine.


Problem:
The Bike starts right up, but idles around/slightly above 1000 RPM.  Also to note, my battery warning light comes on at startup, but turns immediately off at the first rev and never comes back on(Anyone Else?).  The main problem I'm facing is that I have very jerky, delayed, poor acceleration below about 2500 RPM.  The problem seems to go away once the bike has been running for about 15 minutes or so.  

Possible Diagnosis(Untested):
Tracking potential root causes from other posts ive read.

  1. Low Battery
  2. Bad Ignition Coils 
  3. Bad/Dirty Fuel Injectors
  4. Replace Spark Plugs
  5. Replace Fuel Filter
  6. Hall Effect Sensor (No Idea what this is but flippin $200 to replace)
  7. Crankcase Breather hose (Please god $15 fix)


The first couple of things im gonna try are the cheaper options aka charging the battery, fuel filter, and spark plugs.  I'm gonna have a guy test the coils this friday. (Fingers crossed cause them thangs are about $200 each)  I'll keep you guys updated

    

2Back to top Go down   Low RPM Low Power Jerky Acceleration Empty Re: Low RPM Low Power Jerky Acceleration on Wed Aug 12, 2020 9:41 am

Laitch

Laitch
Life time member
Life time member
@Ohnij wrote:. .  . my battery warning light comes on at startup, but turns immediately off at the first rev and never comes back on(Anyone Else?). 
If by never comes back on you mean doesn't turn on again while riding until the next startup, that's how it's supposed to work when indicating a functioning alternator.


__________________________________________________
1995 K75 77,000 miles
Low RPM Low Power Jerky Acceleration Usa-lo10
    

3Back to top Go down   Low RPM Low Power Jerky Acceleration Empty Re: Low RPM Low Power Jerky Acceleration on Wed Aug 12, 2020 5:33 pm

MartinW

MartinW
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Start with giving it a tune up. Check the valve clearances, check and or replace the spark plugs, adjust the idle mixture, this requires a  exhaust gas analyser or using the lean drop method, check for vacuum leaks and balance the throttle bodies using a set of vacuum gauges, don't touch the throttle body screws with the blue paint . Also check and or replace air filter and fuel filter.
Regards Martin.



Last edited by MartinW on Wed Aug 12, 2020 5:36 pm; edited 1 time in total (Reason for editing : addition)


__________________________________________________
K75s Hybrid
    

4Back to top Go down   Low RPM Low Power Jerky Acceleration Empty Re: Low RPM Low Power Jerky Acceleration on Thu Aug 13, 2020 4:10 am

Arlina

Arlina
Life time member
Life time member

  1. Low Battery -> Check voltage with contact off, should be 12,8V. Contact on can drop to 12,5V , starting may not drop under 10V or the battery is gone.
  2. Bad Ignition -> Coils  See #9
  3. Bad/Dirty Fuel Injectors -> Possible, but why the bike runs fine warm.... Nah, don't think so.
  4. Replace Spark Plugs  -> As MartinW say, do a full service, including #8
  5. Replace Fuel Filter -> Check it first. Clean the inlet and blow it through, some fuel will come out. Good filter you can blow through with no pressure.
  6. No hall, forget it.
  7. Crankcase Breather hose (Please god $15 fix) -> Always ckeck that bugger.
  8. Check EVERY electrical connector on the bike. (Is on the BMW list every 15000km (Did anyone do that? ))
  9. https://www.kforum-tech.com/electrical/EFI/bike-wont-start-EN.htm  and scroll down.


__________________________________________________
Low RPM Low Power Jerky Acceleration Eu-log10  K1100RS/LT - R1200RT - R1100RS (RIP) - Cagiva SST 350 Ala Verde - K75LT project
    

5Back to top Go down   Low RPM Low Power Jerky Acceleration Empty Re: Low RPM Low Power Jerky Acceleration on Fri Aug 14, 2020 1:24 am

Ohnij

Ohnij
active member
active member
Whelp I'm still waiting on parts and haven't done anything to the bike yet, but now the bike feels like it has very little power throughout the entire RPM band.  No idea whats going on.  We'll see what happens this weekend. But heres whats gonna get done.

1. Replacing Fuel Filter
2. Cleaning Fuel Injectors (Also bought a Injector Service kit from MrInjector but waiting on shipment)
3. Replacing Air Filter
4. Inspecting Spark Plugs (Also being replaced waiting on parts)
5. Testing Coils
6. Water Pump Seal, Impeller, Impeller Rod replacement (Not related to above)
7. Servicing Rear Master Cylinder (Might need a rebuild kit TBD Also unrelated)

    

6Back to top Go down   Low RPM Low Power Jerky Acceleration Empty Low power on Fri Aug 14, 2020 2:01 am

daveyson

daveyson
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Running rich? Temp sensor?


__________________________________________________
11/1985 bmw k100rt (late model)  Vin. 0090567
    

7Back to top Go down   Low RPM Low Power Jerky Acceleration Empty Re: Low RPM Low Power Jerky Acceleration on Fri Aug 14, 2020 9:11 am

Laitch

Laitch
Life time member
Life time member
@Ohnij wrote: But heres whats gonna get done.
You might do a compression test before all that, and check your valve clearances if you haven't in the last 20K miles or so.


__________________________________________________
1995 K75 77,000 miles
Low RPM Low Power Jerky Acceleration Usa-lo10
    

8Back to top Go down   Low RPM Low Power Jerky Acceleration Empty Re: Low RPM Low Power Jerky Acceleration on Mon Aug 17, 2020 1:00 am

Ohnij

Ohnij
active member
active member
UPDATE:  Spent all day yesterday in the garage working on the K.  Replaced the Water pump seal impeller and impeller shaft(Not related to the issue but she was leaking a ton and had to be fixed).  Replaced the air filter.  Checked my Valve Clearances(All in Spec).  K is still not running well.  In fact, everyday since noticing the problem, its been getting worse and worse.  After working on the bike and putting it back together, I couldn't even ride it out of the moto garage.  Its spending the weekend there. Tracking the remaining items:


  • Fuel Filter Change
  • Cleaning Fuel Injectors
  • Test Ignition Coils
  • Replace Spark Plugs
  • Check Throttle Body Vacuum Caps and Boots
  • Compression Test (Doubt this is the problem)



Last edited by Ohnij on Tue Aug 18, 2020 3:15 am; edited 2 times in total

    

9Back to top Go down   Low RPM Low Power Jerky Acceleration Empty Re: Low RPM Low Power Jerky Acceleration on Mon Aug 17, 2020 9:20 am

Laitch

Laitch
Life time member
Life time member
Take off the cap assembly. Check all the fuel line couplings for tightness and the fuel lines for cracks. Replace the fuel filter if you don't know how old it is or it's several years old. Those are common fault sources.


__________________________________________________
1995 K75 77,000 miles
Low RPM Low Power Jerky Acceleration Usa-lo10
    

10Back to top Go down   Low RPM Low Power Jerky Acceleration Empty Re: Low RPM Low Power Jerky Acceleration on Tue Aug 18, 2020 9:51 pm

Ohnij

Ohnij
active member
active member
Another Update:
  So i replaced the fuel filter and cleaned out the injectors.  Both were absolutely filthy.  The filter looked like the original.  When i dumped out the fuel from it, it looked as though it was full of rusty sand.  Grit was all in the injectors.    So i put the bike back together and it took about 15 seconds for it to fire up.  I imagine cause fuel needed to circulate.  Bike started, idle looked good.  Went out for a test ride.  Pulled the throttle and damn near flew off the bike.  The response is perfect.  Excellent even, smooth, power throughout the entire band.  

There you have it, for others who may have experienced similar issues.  Bike was running SUPER lean cause of clogged fuel system.  Could have been either filter or the injectors, but more than likely a combination of both.  Love this bike more than when i bought it.  

Total Cost to Fix:  

  1. Fuel Filter: $20 
  2. Carb Cleaner: $5
  3. DIY Garage Membership: $50 per month (Has all tools needed including Motion Pro Injector Cleaner and Ultrasonic Cleaner)


Now on to the rear master cylinder....

    

11Back to top Go down   Low RPM Low Power Jerky Acceleration Empty Re: Low RPM Low Power Jerky Acceleration on Wed Aug 19, 2020 3:20 am

MartinW

MartinW
Life time member
Life time member
Rear master cylinder conversion. http://www.motobrick.com/index.php/topic,9364.msg116179.html#msg116179
Regards Martin.


__________________________________________________
K75s Hybrid
    

12Back to top Go down   Low RPM Low Power Jerky Acceleration Empty Re: Low RPM Low Power Jerky Acceleration on Wed Aug 19, 2020 9:02 am

Point-Seven-five

Point-Seven-five
Life time member
Life time member
Don't waste time and money on rebuilding your rear master cylinder.  Do Martin's retrofit and go for a ride. 

I've done 3(or is it 4?) of these retrofits and they all work really well.


__________________________________________________
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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