Author Topic: K75 2V hesitates when starting from idle  (Read 15650 times)

Offline brichbk

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K75 2V hesitates when starting from idle
« on: April 13, 2018, 10:40:09 PM »
I've been trying to diagnose why my 1993 K75RT will die or hesitate to accelerate RPM's when starting from a stop if it's not above 2k RPM's.  I start the bike, let it warm up with full choke, then with full choke or half choke or no choke it will die unless I keep the RPM's over 2,000 and let the clutch out slowly and I mean slllowwwwlllyyyyyy.  There is a noticeable hesitation of when the RPM's increase when I quickly roll on the throttle when I slowly roll the throttle the hesitation is not as noticeable.

After about 10 minutes of stop and go traffic it still requires the RPM's to be over 2,000 or it luggs.  If I downshift from 3rd to 2nd and go around a sharp corner the RPM's drop to idle (1100) and then when I give it throttle it luggs like I'm in 5th gear going 20mph (even though I'm in 2nd gear).


I'm looking for some advice and suggested items to check first.

When I start it from cold with full choke it idles at 1300
then half choke 1100
and no choke 1000-1100

What I've done so far:
I've replaced the Z-shpaed breather hose on the top of the crankcase.  Because it was cracked.
I checked for cracks around the intake boots by spraying carb cleaner around them to see if the RPM's changed, they didn't.
I don't hear a "click" from the TPS at any position, but I'm going to check this with an ohms meter.
I'm pulling the fairings off and the tank to check for any more air leaks.
Next I'll be pulling the gas tank to get to the air filter.  Do I really have to pull the gas tank to get to the air filter?


What I haven't checked yet:
Spark Plugs, but it doesn't have any problem starting or running except at launching from a dead stop.
Air Cleaner
Fuel pump, injectors, throttle bottle, fuel filter - although it seems to run fine other than the launch issue


What I found to be weird:
This hose which looks like it's broken and I have no idea what it's supposed to connect to.  I checked for vacuum when the bike was running but nothing.  It connects to the front of the motor.  it is on the right side in front of the air box.



I tried adjusting the TPS by loosening this screw (and the otherside screw) and moved the TPS to the top and bottom and inbetween to try to find the "click".



Here's my crankcase breather hose.  The crack was on the end that connects to the airbox.




  • Central Valley California
  • 1993 BMW K75RT // 1982 Honda Nighthawk 650sc

Offline Laitch

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Re: K75 2V hesitates when starting from idle
« Reply #1 on: April 13, 2018, 11:39:55 PM »
Do I really have to pull the gas tank to get to the air filter?
No.

  • 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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Offline brichbk

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Re: K75 2V hesitates when starting from idle
« Reply #2 on: April 14, 2018, 12:43:44 AM »
Took the plug off my TPS and found the center probe and hole covered in green stuff. I’m thinking this might be my problem. Any suggestions on how to clean this?  Scrape with a screwdriver?
  • Central Valley California
  • 1993 BMW K75RT // 1982 Honda Nighthawk 650sc

Offline Skunky

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Re: K75 2V hesitates when starting from idle
« Reply #3 on: April 14, 2018, 04:05:43 AM »
Hi Mate - Definitely need to scrape the green shite out of the TPS first and spray with Deoxit. You should check you plugs and leads and fuel filter before messing around with the settings on the TPS. A poor quality plug can cause exactly the problems you're having.
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Offline Inge K.

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Re: K75 2V hesitates when starting from idle
« Reply #4 on: April 14, 2018, 04:52:31 AM »
This hose which looks like it's broken and I have no idea what it's supposed to connect to.  I checked for vacuum when the bike was running but nothing.  It connects to the front of the motor.  it is on the right side in front of the air box.

If it ends up at spigot just behind the cam chain cover at the front right corner of the engine block it's the
breather for the fuel tank.
It was bulletin from BMW that the hose should be removed and the connection at the engine end closed as
it didn't function that good.......then the tank is open to the atmosphere, like the euro models.

Just put a screw with a unthreaded part into the hose to close it off.
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Offline bizzaro

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Re: K75 2V hesitates when starting from idle
« Reply #5 on: April 14, 2018, 08:56:31 AM »
Just want to mention you have done a superb job of posting here brichbk. http://www.motobrick.com/index.php?topic=1522.0
  • Vermont
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Offline The Mighty Gryphon

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Re: K75 2V hesitates when starting from idle
« Reply #6 on: April 14, 2018, 09:22:22 AM »
I doubt your problem is with the TPS.  Have you pulled a spark plug to see if the engine is running lean or rich? 

I suspect your engine is running lean and starving for fuel.  Possibly a plugged fuel pump or plugged fuel filter, two places you say you still need to check.  Another remote possibility is a faulty fuel pressure regulator that is not providing adequate fuel pressure in the rail.

Before chasing anything down, pull a spark plug.
  • 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 Scott_

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Re: K75 2V hesitates when starting from idle
« Reply #7 on: April 14, 2018, 09:55:51 AM »
Just FYI for you Brichbk, the "choke" is not a choke in the sense of cutting off air like one would assume, but it is only a throttle advance, nothing more.
How does the outlet of the exhaust look, black and sooty, or other.
Check to see that you don't have a critter nest in your airbox.
I agree with MG, check your fuel filter as well.
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Offline John Lang

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Re: K75 2V hesitates when starting from idle
« Reply #8 on: April 14, 2018, 01:48:49 PM »
My K75C started right up after its winter nap but ran roughly and stalled when I let out the clutch in 1st gear. After 42,000 km (16,000 km recommended), one of the Bosch x5dc plugs had somehow died over the winter. New Champion 810s and it is humming once more.
  • Ottawa, ON Canada
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Offline brichbk

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Re: K75 2V hesitates when starting from idle
« Reply #9 on: April 14, 2018, 05:43:49 PM »
Pulled my plugs today.  Number 3 looks fouled and has some yellow/orangish coloring on the white ceramic part of the plug.








It looks to me like they need replacement.  I am planning on using the NGK DR7EB.
  • Central Valley California
  • 1993 BMW K75RT // 1982 Honda Nighthawk 650sc

Offline Scott_

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Re: K75 2V hesitates when starting from idle
« Reply #10 on: April 14, 2018, 08:11:10 PM »
When you get your new plugs, make sure that they have the rounded top on them....... some only come with the threaded stud, and that won't work alone without the proper cap.
Some come with the cap in the box, some don't. A local small engine shop should have them if you need them.
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1995 K1100LT 0302044
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Offline stokester

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Re: K75 2V hesitates when starting from idle
« Reply #11 on: April 14, 2018, 09:02:12 PM »
Hi Mate - Definitely need to scrape the green shite out of the TPS first and spray with Deoxit. You should check you plugs and leads and fuel filter before messing around with the settings on the TPS. A poor quality plug can cause exactly the problems you're having.
Agree...


Have you ever checked your valve clearances?
  • Yorktown Virginia
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Offline Laitch

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Re: K75 2V hesitates when starting from idle
« Reply #12 on: April 14, 2018, 09:22:46 PM »
It looks to me like they need replacement.  I am planning on using the NGK DR7EB.
Their gaps look wider than .9mm for sure although I am viewing them from the other side of the country. :giggles
  • Along the Ridley in Vermont.
  • 1995 K75 89,000 miles
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Offline Martin

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Re: K75 2V hesitates when starting from idle
« Reply #13 on: April 14, 2018, 11:50:18 PM »
+1 Gaps look way to big what are they?

Regards Martin.
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Offline brichbk

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Re: K75 2V hesitates when starting from idle
« Reply #14 on: April 15, 2018, 12:46:44 PM »
+1 Gaps look way to big what are they?

Regards Martin.


#1 & 2 were ok, but 3 was way off.  Replaced them anyways with some Bosch plugs from the local dealer.  I haven't got a chance to test it yet got hit with a pretty nasty cold.  :musicboohoo: [size=78%] I also checked the air filter, no critters and the filter looked ok.[/size]
  • Central Valley California
  • 1993 BMW K75RT // 1982 Honda Nighthawk 650sc

Offline brichbk

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Re: K75 2V hesitates when starting from idle
« Reply #15 on: April 20, 2018, 02:05:16 PM »
Installed a new Napa Gold 3032 Fuel Filter today, the bike stills hesitates when starting.  I let it warm up for a long time and took it for a little ride (less than 5 miles) and at the first stop I pulled in the clutch and the RPM's decreased until it just died (2500RPM -->500RPM and died).


So, far I've replaced the spark plugs and the fuel filter.  What's the next step?  Test the Fuel Pump or pressure regulator?



Here's a video I took of it idling in the driveway before the ride and I'm rolling and blipping the throttle.

  • Central Valley California
  • 1993 BMW K75RT // 1982 Honda Nighthawk 650sc

Offline brichbk

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Re: K75 2V hesitates when starting from idle
« Reply #16 on: April 20, 2018, 06:21:08 PM »
Checked the fuel pump flow by disconnecting the fuel filter and running the fuel back into the tank.  It seems like it's pumping it out well enough.  I put my finger over the hose and wasn't able to stop the flow.


  • Central Valley California
  • 1993 BMW K75RT // 1982 Honda Nighthawk 650sc

Offline bizzaro

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Re: K75 2V hesitates when starting from idle
« Reply #17 on: April 20, 2018, 08:57:25 PM »
Have you checked intake manifolds for leaks with propane? Adjusted your throttle bodies?
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Offline richarddacat

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Re: K75 2V hesitates when starting from idle
« Reply #18 on: April 20, 2018, 09:03:11 PM »
I going with new fuel injectors, that would be my bet.  :popcorm
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Offline The Mighty Gryphon

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Re: K75 2V hesitates when starting from idle
« Reply #19 on: April 20, 2018, 09:11:44 PM »
Sticky barn door in the MAF sensor??? 

Throttle lag in the Jetronic vs. the relatively instantaneous response of the Motronic is readily apparent to anyone who owns both systems.  The barn door is the source of that lag.  It relies on the suction of the cylinders to pull the air that opens it.  If it isn't opening, no amount of throttle is going to make the engine increase power output.
  • 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 brichbk

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Re: K75 2V hesitates when starting from idle
« Reply #20 on: April 21, 2018, 12:57:35 AM »
Have you checked intake manifolds for leaks with propane? Adjusted your throttle bodies?


I haven't messed with the throttle bodies and tested intake manifolds and found no leaks.
  • Central Valley California
  • 1993 BMW K75RT // 1982 Honda Nighthawk 650sc

Offline Laitch

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Re: K75 2V hesitates when starting from idle
« Reply #21 on: April 21, 2018, 07:02:06 AM »
I haven't messed with the throttle bodies and tested intake manifolds and found no leaks.
Anyone who buys a used bike should do a tuneup on it from the start rather than jumping from one symptom treatment to another.

Part of a tuneup on a used K-bike is to clean the electrical connectors using a high quality cleaner like DeoxIT—the four-pin connector under the tank, the ignition switch connector, the ignition control unit connector, the fuel injection control unit connector. Be sure they fit tightly together. You've already replaced the fuel filter, the Z-hose, checked the air filter and checked for vacuum leaks.  After you've cleaned all the connectors, you could balance the throttle bodies.

Or not.
  • 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.
https://tinyurl.com/RillRider

Offline Martin

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Re: K75 2V hesitates when starting from idle
« Reply #22 on: April 21, 2018, 03:42:56 PM »
As per Laitch but also check the mixture. With your engine warmed up and idling at 1000 rpm press the green starter button. If the mixture is correct the revs should stay the same or rise slightly. If the engine dies the mixture is too rich, if the revs increase significantly it is too lean. Adjustment is made by removing the rubber plug on top of the RHF corner of the air box. You need to insert a 5mm allen key. There are a couple of method for determining the mixture, one is the lean  drop method, just type in lean drop method. The easiest is by using an exhaust gas analyser, I purchased a Gunson about 20 years ago and it has worked well. If you go the Gunson route patience is the key and follow the instructions. Also it is a light weight piece of equipment and treat it with care do not drop it or lend it out, and always purge it thoroughly after use. TMG has bought one and may want to add to this. I think they can be had for about $250.00 US try Ebay.
Regards Martin.
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  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline brichbk

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Re: K75 2V hesitates when starting from idle
« Reply #23 on: April 22, 2018, 12:15:02 AM »
Thank you to all those who have chimed in.  I greatly appreciate it.  I'll work on cleaning all the connections next and might even look at replacing the fuel pump.  Although I don't want to just replace parts.  This K75 is definitely a bit more complex than my '82 nighthawk.


I took the tank off today to get a better look at what was under it and took a better look at the air filter, which was pretty bad and so I replaced it.  I was also cleaning around the fuel injectors today and noticed that the #2 (middle) injector looked like it was leaking where it enters the engine.  I didn't use any thing other than a screwdriver and can of air to clean so the wetness didn't come from anything I was doing.  Tell me if this picture looks normal or not.



Thanks again for all your help.  I'll look into getting a manometer to balance the throttle bodies and my other bike carbs probably could use a little balancing.
  • Central Valley California
  • 1993 BMW K75RT // 1982 Honda Nighthawk 650sc

Offline The Mighty Gryphon

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Re: K75 2V hesitates when starting from idle
« Reply #24 on: April 22, 2018, 10:24:02 AM »
I went back to the start of this thread, and have a question.  Please forgive me if you have already answered this.   Is this a new to you bike?  Did it run properly for you in the past, or did this problem come with the bike?
  • 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"

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