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Author Topic: 1987 K75 poor running  (Read 9035 times)

Offline kenrams

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1987 K75 poor running
« on: October 20, 2019, 01:18:32 PM »
Hi guys

Working my way through a recent K75 purchase that the PO had lost interest in getting properly running. It was his fathers and was parked up in his garage 6 or 7 years ago. 50,000 miles. Symptoms are that it starts fine but once the throttle is opened it runs really rough and has no pull at all.

So I systematically went through the bike and found the Z pipe and the big 90 pipe to the airbox split. I also replaced the plugs, air filter, fuel filter, and adjusted two tight exhaust valves. Adjusted TPS switch. The PO had also replaced the fuel injectors. The compression test is good. Fuel pressure was measured using an inline meter, at 32 psi.

Still runs rubbish.

So while thinking about next logical step, I noticed that the idle stop screw was maybe 1/8 - 1/4 inch away from the stop.  I removed and freed the throttle cable from the perch to eliminate binding, routing and throttle cable adjustment as the culprit.
 I then looked at the "choke" cable adjustment to see if that was adjusted incorrectly. I backed the knurled knob until I could see the cable slacken. No change was detected to the idle stop "gap". Weirdly, when I engage the choke lever it has zero effect on the idle stop gap. ( the mechanism at the throttle body rotates fine) 

Even screwing the idle stop out fully didn't make contact with the stop.

Anyone got an explanation or suggestion as to what to do next?
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  • Asheville, NC, USA
  • 1985 K100, 1990 K75, 1982 R100

Offline kenrams

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Re: 1987 K75 poor running
« Reply #1 on: October 20, 2019, 01:28:22 PM »
I also checked the Air Flow sensor for ease of movement and cleaned the FI control contacts. Also checked for sparks on all three cylinders.
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  • Asheville, NC, USA
  • 1985 K100, 1990 K75, 1982 R100

Offline Laitch

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Re: 1987 K75 poor running
« Reply #2 on: October 20, 2019, 01:49:15 PM »
Have you balanced the trottle bodies using manometers?
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  • Along the Ridley in Vermont.
  • 1995 K75 89,000 miles
I wept because I had no radials until I met a man who had no splines.

Offline kenrams

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Re: 1987 K75 poor running
« Reply #3 on: October 20, 2019, 01:54:46 PM »
Thanks, that is the next thing on the list but first I wanted to figure out the idle stop issue. I've never sync'd throttle bodies before so will have to do some research into the process.
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  • Asheville, NC, USA
  • 1985 K100, 1990 K75, 1982 R100

Offline kenrams

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Re: 1987 K75 poor running
« Reply #4 on: October 20, 2019, 02:52:44 PM »
Ok found the issue. It was the TPS adjustment that was holding the throttle bodies open - duh !

Ok on to TB synching. I'll be buying some analyzers( any recommendations ?)  today
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  • Asheville, NC, USA
  • 1985 K100, 1990 K75, 1982 R100

Offline johnny

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Re: 1987 K75 poor running
« Reply #5 on: October 20, 2019, 03:39:07 PM »
carbtune and gs911
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Offline kenrams

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Re: 1987 K75 poor running
« Reply #6 on: October 27, 2019, 03:12:47 PM »
So I just got the Carbtune Pro 4 delivered. I cut 4 inches off each hose and inserted the restrictors and connected the carbtune to the throttle bodies - restrictor end to the engine. I warmed up the bike first. Here's the funny thing - the pipes inside the carbtune barely move at all - no matter what the revs ! Do I have a bad tool or is there anything else I could have done ?
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  • Asheville, NC, USA
  • 1985 K100, 1990 K75, 1982 R100

Offline johnny

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Re: 1987 K75 poor running
« Reply #7 on: October 27, 2019, 05:07:31 PM »
greetings...

you gotts to start engine and let it run until fan cycles on... turn it off and hook up hoses...

then follow the instructions posted here at the world famous motobrick.com...  where to start at what rpm and what to turn and not what to turn...

carbtune search returned this in less than a second...

http://www.motobrick.com/index.php/topic,7964.msg58423.html#msg58423

j o
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Offline kenrams

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Re: 1987 K75 poor running
« Reply #8 on: October 28, 2019, 01:23:40 PM »
Thanks Johnny, I did all that. The issue was that the K75 produces a reading lower than 8cmHg and so has to be hung upside down to get a reading!
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  • Asheville, NC, USA
  • 1985 K100, 1990 K75, 1982 R100

Offline johnny

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Re: 1987 K75 poor running
« Reply #9 on: October 28, 2019, 03:10:33 PM »
greetings...

you mean with hoses outta the bottom like this...


* download.jpeg (9.52 kB . 168x299 - viewed 479 times)

poast up some photos so we can see what you see...

j o
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Offline kenrams

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Re: 1987 K75 poor running
« Reply #10 on: October 28, 2019, 04:10:35 PM »
Yup, that's the way (which is opposite to the few online instructional videos). Here's the setup with ignition off


* P1010323.JPG (57.49 kB . 768x576 - viewed 493 times)

And here it is with the engine running at idle (fourth input not used obviously)


* P1010328.JPG (51.85 kB . 768x576 - viewed 523 times)

It looks not bad but unfortunately, the bike still revs very poorly. Poor response, poor pickup, occassional backfires. I have searched the site and carried out everything that might be causing the issue and I am now considering taking it to the shop but I really want to fix it myself.
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  • Asheville, NC, USA
  • 1985 K100, 1990 K75, 1982 R100

Offline Martin

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Re: 1987 K75 poor running
« Reply #11 on: October 28, 2019, 04:27:04 PM »
Part of owning a K75 is supposed to be able to put up with the backfiring. This is untrue backfiring can be eliminated.
1/ Correctly adjust the TPS.
2/ Check for air leaks at the throttle bodies and "Z" hose and eliminate.
3/ Check for exhaust leaks especially header to muffler and eliminate.
4/ Correctly adjust the mixture and balance the throttle bodies.
5/ Have the injectors cleaned and checked for the correct spray pattern.
6/ Do not have the throttle partially open on overrun down hills or when slowing fully close it.
The only time mine backfires now is if I don't follow 6/.
Regards Martin.
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  • North Lakes Queensland Australia
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Offline johnny

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Re: 1987 K75 poor running
« Reply #12 on: October 28, 2019, 04:33:47 PM »
greetings...

needs miles and snake earl...

1st tank 1 bottle of marvel mystery oil...

2nd tank 1 bottle of marvel mystery oil...

3rd tank 1 bottle of techron...

4th tank 1 bottle of techron...

5th tank straight no corn ethyl...

do this in 1 day or 2 continous days...

redo the carbtune...

ride it... wants miles...

j o
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Offline Laitch

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Re: 1987 K75 poor running
« Reply #13 on: October 28, 2019, 04:46:07 PM »
In addition to Martin's recommendation to check leaks in the rubber manifold connections, check the coolant temperature sensor to be verify that it functions correctly so it isn't fouling the fuel mixture by incorrectly reading engine temperature. A chart is in Vogel's troubleshooting guide on the site. What color are the the spark plug electrodes after a ride? Are they sooty or chalky? Are the coil terminals clean? Have you resistance tested them? Have you run the engine in the dark to check for spark leakage at the coils and HT leads.

A recent complainant with a sluggish engine claims to have discovered the voltage regulator was providing inconsistent output. Replacing it seemed to remedy poor running, so determining its output at various revs using a multimeter might be useful. Avoid replacing parts without determining first if they are malfunctioning.
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  • Along the Ridley in Vermont.
  • 1995 K75 89,000 miles
I wept because I had no radials until I met a man who had no splines.

Offline kenrams

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Re: 1987 K75 poor running
« Reply #14 on: October 28, 2019, 05:08:33 PM »
PArt of the issue is that it runs so poorly it would be hazardous to take out on the roads. I also live on a steep hill and will not be able to push it back up the hill if it dies on me. So I cant do the classic run/hit the kill switch/check plug color.

I've already replaced the usual rotting hoses (Zhoses and 90deg plenum) and sprayed WD40 around to check for other leaks around the TBs.

I've not done the coolant sensor check so I'll do that later. Also, I'll check the coils and run the bike in the dark. Voltage output is good rises to about 13,4v after startup and revvin around 3000rpm. 

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  • Asheville, NC, USA
  • 1985 K100, 1990 K75, 1982 R100

Offline stokester

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Re: 1987 K75 poor running
« Reply #15 on: October 28, 2019, 05:17:17 PM »
Quote from: kenrams on October 27, 2019, 03:12:47 PM
So I just got the Carbtune Pro 4 delivered. I cut 4 inches off each hose and inserted the restrictors and connected the carbtune to the throttle bodies - restrictor end to the engine. I warmed up the bike first. Here's the funny thing - the pipes inside the carbtune barely move at all - no matter what the revs ! Do I have a bad tool or is there anything else I could have done ?
I use a Carbtune Pro also and do not have this problem.  Did you T the hose to the FPR?

Using carb, brake cleaner or propane is much better than WD-40.

Should be able to send a pic of my setup tomorrow.
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  • Yorktown Virginia
  • '94 K75S Dakar Yellow - '93 K75S Seiden Blau - '91 R100RT Bermuda Blue- '78 R100S Smoke Red

Offline The Mighty Gryphon

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Re: 1987 K75 poor running
« Reply #16 on: October 28, 2019, 05:18:18 PM »
There is no mention of spark plugs.  What are you running?   What does the sparky part look like?  What does the connector part look like? 

Does the bike have OEM wires?

Can you post some photos of the spark plugs?  Both the sparky part and connector end.

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  • In my garage in Marilla, NY
  • '91K100RS White/Blue
Current:
'91 K100RS16V "Moby Brick Too"

Past:
'94 K75RT "Ilsa, She Wolf of the SS"
'92 K100RS16V "Moby Brick" (RIP, deceased in a vehicular assault)
'94 K75S Special Edition Dakar Yellow "Cheetos"
'89 K100RS Special Edition "Special Ed"

Offline daveson

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Re: 1987 K75 poor running
« Reply #17 on: October 28, 2019, 07:22:54 PM »
I would also ask the PO for more detail what adjustments were made and re check them. Did he get good injectors? Maybe eventually check the spray pattern, after disabling the coil earth's.

Plus a full service,  clean the earth's,  plugs and ICU.

I'm surprised about 75's backfiring, mine was (and is) poorly maintained, but I couldn't get it to backfire if I tried.
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  • Victoria, Australia
  • Current;'85 K100RT~100,000km; four other bricks. Past; 1500 Vulcan, V Star 650, KLX 250(dirt bike) TT250(dirt bike)

Offline Martin

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Re: 1987 K75 poor running
« Reply #18 on: October 28, 2019, 09:54:09 PM »
Daveson it seems to be the luck of the draw it was only a problem with K75's. BMW's answer to the problem some do some don't, it causes no harm to the engine. You can reduce it but some will continue no matter what, learn to live with it. I slowly chased my backfiring away, the last couple of pieces in the puzzle were fix the leaking between the muffler and header pipes and get the correct spray pattern on the injectors. I can still induce a backfire if I don't fully close the throttle on down hill runs while coasting.
Regards Martin.
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  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline daveson

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Re: 1987 K75 poor running
« Reply #19 on: October 29, 2019, 12:22:31 AM »
Interesting, that could be worth a new thread, to find the cause.
 (Actually, I have to admit that I used to love the sound of a loud and rough overrun on my old cruiser)
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  • Victoria, Australia
  • Current;'85 K100RT~100,000km; four other bricks. Past; 1500 Vulcan, V Star 650, KLX 250(dirt bike) TT250(dirt bike)

Offline alabrew

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Re: 1987 K75 poor running
« Reply #20 on: October 29, 2019, 11:44:40 AM »
The air temp. sensor values should be checked too. On the '85, it thought it was 150 degrees. Ran best on a 100 degree day.
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  • Birmingham, Alabama
  • 1985 K100, 1991 K100RS
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2005 K1200LT
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Offline stokester

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Re: 1987 K75 poor running
« Reply #21 on: October 29, 2019, 03:00:32 PM »
Quote from: stokester on October 28, 2019, 05:17:17 PM

Should be able to send a pic of my setup tomorrow.
The attached pictures show my '93 K75S at approx 1000 rpm idle (on the high end) and then at 3500 rpm.
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  • Yorktown Virginia
  • '94 K75S Dakar Yellow - '93 K75S Seiden Blau - '91 R100RT Bermuda Blue- '78 R100S Smoke Red

Offline johnny

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Re: 1987 K75 poor running
« Reply #22 on: October 29, 2019, 03:42:28 PM »
greetings...

check your radiator... may be clogged up with buggs and dert...



j o
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Offline Kramsay

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Re: 1987 K75 poor running
« Reply #23 on: October 30, 2019, 09:45:59 PM »
In the process of checking the water temp sensor, I noticed the fan did not spin freely and was pretty much stuck. So I removed the fan and checked brushes. They looked basically new, so I removed the motor, cleaned it up and lubricated it and eventually it spun nice and easy.  Applied 12v to it and it ran fine. I removed the sensor and both thermistors read around 2.5 kohms. I heated it up with a heat gun and  the resistance dropped. I will put it in a pan and heat to compare with the Vogel chart. Don’t expect it to be the cause of my problem. Radiator was flushed and looks new.

I removed the coils, cleaned up the ground, checked primary resistance. 

Just to reiterate, the plugs are new NGK, all have sparks and the fuel injectors are also new. When it was parked up years ago it was due to the main oil seal failure.
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Offline Laitch

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Re: 1987 K75 poor running
« Reply #24 on: October 30, 2019, 10:45:38 PM »
Quote from: Kramsay on October 30, 2019, 09:45:59 PM
Don’t expect it to be the cause of my problem. Radiator was flushed and looks new.
When it was parked up years ago it was due to the main oil seal failure.
What do you expect to be the cause? Years of neglect can cause deterioration of many components, especially rubber and electrical components.
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  • Along the Ridley in Vermont.
  • 1995 K75 89,000 miles
I wept because I had no radials until I met a man who had no splines.
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