Author Topic: Stuttering under part-throttle  (Read 4573 times)

Offline johnny

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Re: Stuttering under part-throttle
« Reply #25 on: May 22, 2017, 07:13:44 AM »
greetings...

murph has the ccs100 whole and parts...

https://www.murphskits.com/product_info.php?manufacturers_id=6&products_id=422

j o
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Offline Scott_

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Re: Stuttering under part-throttle
« Reply #26 on: May 22, 2017, 07:32:22 AM »
Thanks for the link JO.
I'm debating replacing the unit on my '97, nice to see I can just purchase the canister/cable assy that's bad and not the entire kit....
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Offline The Mighty Gryphon

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Re: Stuttering under part-throttle
« Reply #27 on: May 22, 2017, 09:47:43 AM »
Be aware that the giant airboxes on Jetronic bricks make it difficult if not impossible to install the throttle cable without messing up the throttle action.  The Motronic units with the hoses to the throttle bodies make for a much easier install. 

I was very lucky to find a "cable interface unit" from Motorcycle Setup PTY to connect all the cables to the throttle body. 
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Offline Martin

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Re: Stuttering under part-throttle
« Reply #28 on: May 22, 2017, 01:56:27 PM »

E30  have you checked your fuel hoses for deterioration, have you checked your valve clearances. And you might want to give running a couple of doses of Techron through the system.
Regards Martin
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Offline E30_Crazy

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Re: Stuttering under part-throttle
« Reply #29 on: May 23, 2017, 07:58:51 AM »
Laitch, yes filter was changed, pulled the pump out and cleaned the screen and tank.


Fuel hoses are still looking good. Believe they were changed just a couple years ago.


Gonna change the FPR, and if that doesn't fix it I'm gonna look for another ECU, since it seems to be slowly getting worse, and in the same way last time when it was the ecu
  • Newport News, Virginia
  • '85 K100

Offline Laitch

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Re: Stuttering under part-throttle
« Reply #30 on: May 23, 2017, 02:33:15 PM »
Gonna change the FPR, and if that doesn't fix it I'm gonna look for another ECU, since it seems to be slowly getting worse, and in the same way last time when it was the ecu
That isn't a productive way to go about solving this problem although it does keep parts suppliers in business. We all want that.

Have you checked your valve clearances, air filter, vacuum leaks then done a throttle body balance? You've already change the plugs and fuel filter. The other elements I've described would complete what is called a tuneup. When was that last done?
  • Along the Ridley in Vermont.
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Offline E30_Crazy

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Re: Stuttering under part-throttle
« Reply #31 on: May 28, 2017, 03:19:04 PM »
No definite date or even surety as to when it was last all done. I was all over this and other sites reading up on the K100 before buying mine, so I knew what questions to ask and what to look for. IIRC, most anything maintenance and tuneup was done by PO. Splines, filters, plugs, etc.


I have a spare FPR, so might as well try. Gotta dig down to it to check the vacuum lines anyways. Air filter is good. Was gonna replace all the vacuum lines last night, but got sidetracked making a new key pin post for the makeshift lid of the alternate relay box, AKA lower half of stock airbox. After new vacuum lines are in, I'll try an adjustment. Weird how it could just fall out of adjustment suddenly.


Oh, and I just found a vacuum test kit on sale at the local Harbor Freight, so I'll try the TB sync as well, after the vacuum lines are all set
  • Newport News, Virginia
  • '85 K100

Offline E30_Crazy

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Re: Stuttering under part-throttle
« Reply #32 on: May 28, 2017, 03:21:46 PM »
Or TB balance, rather? The TB sync is the mechanical adjustment? The one that can be a PITA?
  • Newport News, Virginia
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Offline Laitch

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Re: Stuttering under part-throttle
« Reply #33 on: May 28, 2017, 03:41:29 PM »
Weird how it could just fall out of adjustment suddenly.
I don't think it has been determined whether something is out of adjustment, obstructed or disconnecting intermittently. The goal is to work in an orderly way toward understanding what is happening.
  • Along the Ridley in Vermont.
  • 1995 K75T 68,000 miles
I wept because I had no radials until I met a man who had no splines.

Offline E30_Crazy

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Re: Stuttering under part-throttle
« Reply #34 on: May 29, 2017, 09:31:03 PM »
So, on my way under the lower airbox half to check out fuel and vacuum lines, I stumbled across a spade connector that had it's stem/crimp poking out of a relatively long rubber boot. Long enough of a boot that it seemed highly unlikely for it to still be connected under the boot ar the top. Pull the boot off, lo and behold a loose spade connector.


It's connection is to a thingy just forward of the FPR on the back side of the throttles (I'll be looking up said thingy and function after this post).


Some of the vacuum likes around the front of the throttles have hardened and begun to crack around the T-fittings, so I won't be ignoring those either. Fuel lines all look good enough for now. Think I'll leave the FPR alone for now. That was I can determine the effect of "thingy" (has an electrical connector, but I'm thinking a vacuum like out the top.... We'll see)




EDIT


Took a wild guess at Google, and nailed it. The vacuum switch. Claims are abound about it not doing anything... But only because BMW removed it after '85. BMW would have then tailored out any requirement for it to be there. On a bike that should have it, I'll go ahead and reconnect it and go for a quick ride.
  • Newport News, Virginia
  • '85 K100

Offline E30_Crazy

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Re: Stuttering under part-throttle
« Reply #35 on: June 02, 2017, 02:50:45 PM »
Still no change. I may be experiencing some very bad mileage aswell. Was pretty sure I had a couple gallons left, fuel pump was fully submerged. Made it about 5 or 10 miles all together after changing fuel filter and checking the pump. Ran out of gas at a stop light. Luckily it was at the turnoff for my sidestreet.


My compound pressure/vacuum gauge only reads 10psi, so I'll need to get another one to test the fuel pump output, and fuel rail regulated pressure.
  • Newport News, Virginia
  • '85 K100

Offline E30_Crazy

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Re: Stuttering under part-throttle
« Reply #36 on: June 09, 2017, 04:07:31 PM »
While checking fuel pressure, is it just during idle that you're expecting around 36psi? I gave some revs and it was down around 20-25 psu at points. Couldn't tell much on the stuttering, since it wasn't in gear/under load.
  • Newport News, Virginia
  • '85 K100

Offline E30_Crazy

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Re: Stuttering under part-throttle
« Reply #37 on: July 02, 2017, 06:55:58 PM »
Just another tidbit.... I seem to have the symptoms of a bad/out of adjustment TPS. But the TPS and wiring all check good, and I've made sure to double-check the adjustment. However, it seems to be when rolling onto throttle slowly from off throttle, when over the 2k RPM fuel-cut. That would tell me the TPS is doing its job (fuel on and off above 2k RPM according to throttle position) albeit possibly on the rich side.


Valve shims are good, vacuum line replaced, TB balance done, new/clean injectors and fuel filter, air and water temp sensors are good, hall sensor good, compression test done. Along with everything I could check with a multi meter on the connectors to the EFI and Ignition ECUs.


I'm going to redo my fuel pressure test. My gauge was leaking all over. Got it traded out at Harbor Freight.
  • Newport News, Virginia
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Offline Laitch

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Re: Stuttering under part-throttle
« Reply #38 on: July 03, 2017, 07:25:44 AM »
The vacuum switch. Claims are abound about it not doing anything...But only because BMW removed it after '85. BMW would have then tailored out any requirement for it to be there.
That's an assumption. It was removed because it interfered with performance. Eliminate it and shield its spade connector with electrical tape. Setting the throttle bodies and setting the correct idle will do, according to many riders' outcomes.

Are you asserting that you checked all values in the troubleshooting guide pertaining to the fuel injection control unit and the ignition control unit and that they conformed to what is presented in their respective charts?
  • Along the Ridley in Vermont.
  • 1995 K75T 68,000 miles
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Offline Martin

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Re: Stuttering under part-throttle
« Reply #39 on: July 03, 2017, 06:19:29 PM »

There are a couple of signs that there could be a problem with the FPR. One is leaking fuel in the vacuum line, and another is when revving  the motor hard ( NOT TO REDLINE) while stationary, it will blow black smoke  which is excess fuelling. I don't know whether this is your problem but it did cure a mates bike.
Regards Martin.
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Offline E30_Crazy

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Re: Stuttering under part-throttle
« Reply #40 on: November 05, 2017, 06:16:39 PM »
That's an assumption. It was removed because it interfered with performance. Eliminate it and shield its spade connector with electrical tape. Setting the throttle bodies and setting the correct idle will do, according to many riders' outcomes.

Are you asserting that you checked all values in the troubleshooting guide pertaining to the fuel injection control unit and the ignition control unit and that they conformed to what is presented in their respective charts?


Yes, all values were measured/verified IAW the Vogel troubleshooting guide.


Was riding it around tonight, after a hiatus for a while. Noticed the low voltage light making a dim appearance. It gets a little bit brighter the higher I go in RPMs. Down lower, or at idle, it seems to go away, or at least much dimmer. I have a digital voltage meter wired up in the triple tree, and get sporadic drops in voltage down to low 12s, sometimes high 11s at higher RPMs. But it's not consistent. Starter and wires have been cleaned a couple times now. Battery ground in clean. Grounds under tank are clean. I may try a different scrotator. It or the voltage regulator may be acting up... This may be its own problem however. I don't know for sure if a slightly low voltage would cause a stutter? Maybe the coil can't draw enough power off the battery alone (new battery just today, too) without a strong output from the scrotator...
  • Newport News, Virginia
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Offline Filmcamera

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Re: Stuttering under part-throttle
« Reply #41 on: November 05, 2017, 06:32:00 PM »
I had a similar issue in reverse when my scrotator was giving out.  I got a nice clean 12.8 V or so at idle but when I revved the bike to 4000+ that voltage went up into the 15 V range.  The engine began running rough after a while at the higher, cruising type revs, I am not sure exactly why but guess that the ECU did not appreciate the higher voltage.  ANyway I had the scrotator rebuilt and have never had a problem since.

So I would certainly take a close look at your scrotator
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Offline Laitch

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Re: Stuttering under part-throttle
« Reply #42 on: November 05, 2017, 10:36:53 PM »
Was riding it around tonight, after a hiatus for a while. Noticed the low voltage light making a dim appearance. It gets a little bit brighter the higher I go in RPMs. Down lower, or at idle, it seems to go away, or at least much dimmer. I have a digital voltage meter wired up in the triple tree, and get sporadic drops in voltage down to low 12s, sometimes high 11s at higher RPMs. But it's not consistent. Starter and wires have been cleaned a couple times now.
How are the regulator brushes looking?
If your bike hasn't been upgraded to a 50 amp, you could try this or these if you need a change.
  • Along the Ridley in Vermont.
  • 1995 K75T 68,000 miles
I wept because I had no radials until I met a man who had no splines.

Offline E30_Crazy

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Re: Stuttering under part-throttle
« Reply #43 on: November 08, 2017, 04:46:57 PM »
Just researched/performed some scrotator testing. Cold/warm and idle/revving and stuttering returned good values on the battery, and both the red and blue leads off the scrotator. Makes me think the scrotator, regulator, and brushes are OK. My on-board voltmeter and/or it's source or wiring must be giving me a false low-voltage.


I was able to snag a video this time around. It usually doesn't act this bad just sitting and revving. Usually only out and riding, under a load. Not that it can tell you much, other than its stuttering, haha.


Oh, and my clutch cable just snapped at the little knurl/tophat that slips into the keeper pin of the lever, so disregard that in the video... It never ends! Haha.


Back to the plan of the FPR next, when I have time to dig to it.



  • Newport News, Virginia
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Offline lmiklosy

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Re: Stuttering under part-throttle
« Reply #44 on: November 08, 2017, 05:43:51 PM »
E30 how were the injectors tested?  The impedance should read 16.5 Ohms but that isn't a sufficient test. Have you listened to them 'tick' at idle?   If you don't have a stethoscope, try the long screwdriver test up to your ear, do at low rpms when the muffler noise is least. At idle you should hear a soft 450cpm tick sound.  Failing a screwdriver test try start a cold engine and run for 30 seconds then shut off. Then starting at the 4 into 1 header feel each header pipe with your fingers to find the cold one(s), there's is your suspect injector.  From the audio I hear a cylinder(s) missing a heartbeat altogether.   Hope that helps.
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Offline E30_Crazy

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Re: Stuttering under part-throttle
« Reply #45 on: November 11, 2017, 02:33:10 PM »
E30 how were the injectors tested?  The impedance should read 16.5 Ohms but that isn't a sufficient test. Have you listened to them 'tick' at idle?   If you don't have a stethoscope, try the long screwdriver test up to your ear, do at low rpms when the muffler noise is least. At idle you should hear a soft 450cpm tick sound.  Failing a screwdriver test try start a cold engine and run for 30 seconds then shut off. Then starting at the 4 into 1 header feel each header pipe with your fingers to find the cold one(s), there's is your suspect injector.  From the audio I hear a cylinder(s) missing a heartbeat altogether.   Hope that helps.
Injectors tested good as far ad ohms could take me. Brand new injectors also. Tested each one from the ECU plug as well, making sure the ohms changed correspondingly to how many injectors were plugged in.


I can try the idle tick, but the issue doesn't really present itself at idle, especially cold
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Offline Laitch

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Re: Stuttering under part-throttle
« Reply #46 on: November 11, 2017, 02:50:38 PM »
Consider performing the Hall sensor test in the troubleshooting guide.
  • Along the Ridley in Vermont.
  • 1995 K75T 68,000 miles
I wept because I had no radials until I met a man who had no splines.

Offline E30_Crazy

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Re: Stuttering under part-throttle
« Reply #47 on: November 11, 2017, 05:47:32 PM »
Consider performing the Hall sensor test in the troubleshooting guide.




I built the DIY LED tester lead, hall sensor seems to work as advertised.


Got the FPR replaces today. Wasn't as bad as in the video, but couldn't tell for sure if it was gone. And couldn't get it under a load very easily without a clutch cable. Gotta wait for that to get here
  • Newport News, Virginia
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Offline E30_Crazy

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Re: Stuttering under part-throttle
« Reply #48 on: November 25, 2017, 05:12:43 PM »
Still spitting and sputtering around 4k after the FPR swap. Does seem to get worse the brighter the battery light illuminates. I bought a batter charger/tender/jump box on black Friday, and it's scrotator check function calls the scrotator bad, even though I couldn't really see anything wrong with a multimeter. Think read somewhere about phases going dead or something, and hard to tell with just a basic multimeter. I will try a voltage regulator, then move on to getting it rebuilt or replaced with a different one.
  • Newport News, Virginia
  • '85 K100

Offline E30_Crazy

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Re: Stuttering under part-throttle
« Reply #49 on: May 18, 2018, 02:47:41 AM »
Got my clutch cable replaced, so now I can do more testing than just revving it in neutral in the garage. I had put some heat on the hall sensor while running, and it seemed to affect the running a little. Think I even had it die once. Put a new hall sensor in today. Idled out of the garage just fine (it was almost midnight, so no revving up to 4 or 6k rpm). Went to pull off, and it lost all acceleration and died after about 10mph. It then would no longer start and/or idle. Seems very similar to the "bad temp sensor no start" scenario. I have checked the temp sensor several times throughout this ordeal, and checked it yet again tonight. Numbers for resistance and temp seem spot on.


So, my next question; looking at the wiring diagram and troubleshooting guide, I see the temp sensor goes to the temp sensing switching unit, and the FI relay. Do these symptoms point more so to one of these than the other?
  • Newport News, Virginia
  • '85 K100

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