Author Topic: My K75 restoration  (Read 9053 times)

Offline mcgyver74

  • Motobrick Curious
  • Posts: 24
My K75 restoration
« on: April 18, 2021, 08:15:33 PM »
Greetings all,
My first real post here at Motobrick, Just became the owner of a 1990 K75s that belonged to my dad for many years,  due to health issues he can no longer ride so gave me the bike.    Sadly it's been sitting outside for years (Under a cover but still) so I have a fair amount of work to do in order to make it safe again. So yesterday the work began





She is looking a bit rough... Sadly she sat outside for a long time and for a few years without even a cover.  She's filthy and does have some body damage that I will need to fix.



 
Man that is a dirty bike




and after airing up the tires, and a bit of wrestling, she's on the trailer.  (Appreciate my bud helping here, and letting me use his trailer :) )




Yeah, she's been sitting for a while...




Unfortunately, she succumbed to the K75 tank rot issue (This is actually the 2nd tank that has been on this bike for this same reason), looks like I need to find a used tank :(




Starting to get dirty, got the old dead battery out (She held a whopping 1.1volts LOL)  I have a new battery





First issue,  the throttle was seized SOLID,  I got scared for a few, but then saw that the throttle bodies moved freely, it was just the twist grip that was stuck.  Some Gentile heat and twisting with a LOT of penetrating oil and I got the tube off,  ugh lots of rust,  but nothing some emery cloth can't fix




After getting the bar cleaned up, I cleaned out the tube and used copius amounts of white lithium grease,  reassembled and she turns smooth and snaps back properly. (Whew, fixed for a grand total of 1 dollar in sandpaper :) )




HOLY hell that's a lot of crap in the belly pan LOL, Since it's been sitting there for years I figured at least let's get some decent oil in there before I try to light her off since I don't know what condition the existing oil is..,  So I want and got a 5 gallon jug of Castrol 20W-50.   I chose this based on the recommendations of Derek At VGG, since it has "All the Minerals and Dinosaurs the bike will need,, and was the cheapest at Walmart" LOL   (It's not staying in there, it's just to run a few heat cycles then I will dump it and put in the good Beltran stuff I bought.  ( I figure a flush is in order before I give her the good stuff)




Got the throttle tube all re-assembled,  now I am fixing some wiring while I wait for the old oil to drain, sadly the rodents got to it, thankfully it was only like 3 wires that needed to be soldered (Didn't get great pics)




Once that was all done, I popped in a new battery and tried to start the engine.  Sadly, in addition to the tank leaking, the fuel pump is also seized solid (I verified power to the pump,  she has juice but it's not making any of the usual whirly noises and it's not pushing fuel)

So for now, I need to find a fuel tank and pump.   

Will update once I have some parts :)




  • Jersey City NJ
  • 1990 K75S
Jersey City NJ
1990 K75S

Offline The Mighty Gryphon

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Re: My K75 restoration
« Reply #1 on: April 18, 2021, 09:41:14 PM »
Looks like a nice project!  Most of the parts look like they are there and the bike has a connection to you.  I did a restore on a similar brick two years ago.  It's a very satisfying feeling seeing the finished product.  This bike sat for 16 years before I got it.  Trust me, it was a lot worse than the photo.


* DSCN3541.JPG (111.82 kB . 768x576 - viewed 857 times)

* DSCN3787.JPG (69.03 kB . 768x576 - viewed 834 times)

I would clean out the tank, do some prep and take it to a good welder to have the leaky spots repaired.  One of my bikes had the tank repaired and it's still holding up very well.

One of the very good things about restoring these bikes is the plethora of good used parts on eBay.  The body parts were made from bulk molding compound, which, while rather heavy responds very well to fairly simple repair techniques. 



  • 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 stokester

  • ^ SuperNatural Motobricker
  • Posts: 815
Re: My K75 restoration
« Reply #2 on: April 19, 2021, 07:29:26 AM »
You've come to the right place for information and a good source for pieces and parts.
Among many other things you have to do be sure to clean and lube the clutch cable barrel at the lever and ensure your fan spins manually.

Good luck and keep us informed of your progress.
  • Yorktown Virginia
  • '94 K75S Dakar Yellow - '93 K75S Seiden Blau - '91 R100RT Bermuda Blue- '78 R100S Smoke Red

Offline AtLarge

  • ^ Proficient Motobricker
  • Posts: 150
  • Not too many bikes. Garage too small.
Re: My K75 restoration
« Reply #3 on: April 19, 2021, 08:16:17 AM »
Definitely salvageable. Good luck on the resto McG. VGG is a good watch.  :welcome
  • IA
  • 1994 K1100RS
1973 Honda CL70-K3, 1975 Kawasaki 350 F9-C, 1994 BMW K1100RS, 2023 Honda CRF300L Rally ABS

Offline mcgyver74

  • Motobrick Curious
  • Posts: 24
Re: My K75 restoration
« Reply #4 on: April 25, 2021, 10:40:39 PM »
Well made SOME progress on the ol Flying brick, some...

I pulled apart the old tank to see if I could salvage it at all, Yeah that's a hard NO dawg :(
The rubber bits literally dissolved into goo...


the fuel pump wasn't much better,  the fuel sending arm was rusted solid as well.



I had a look in hopes I could maybe clean the rust off and salvage the pump but no go, she is locked solid  :(


Was hoping I could get the tank welded, but it's just too far gone, the fuel filter was a solid pile of rust..



In addition, there were bubbles forming on the paint on the TOP of the tank,  a quick check with the cheat poker and I realized there isn't much metal left :(


THANKFULLY I was able to source a decent used tank,  the cap needs a rebuild but she is solid. and she even came with a fuel pump. THe stickers on the gas cap are about all I could salvage from the old tank :(




However sadly she still won't start,  the new pump runs and seems to move fuel, I have spark, and I believe I have compression (Put 5 cc of oil in each cyl to be sure) but no vroom.   Seems I am not getting fuel.

Next steps are to test the fuel pressure, I am not convinced that the pump I got (it came with the tank) is actually good,  when I run it some fuel seems to squirt out of the top seam of the pump itself (In the tank) so Maybe it's not putting enough pressure to open the injectors??

Next steps are to check the fuel pressure (Need to get a gauge) and pick up a noid light so I can confirm I am getting injector pulse...   Hopefully it's just a bad pump and not something more sinister (Like rusted up injectors :( )

Will post more when I learn more :)

  • Jersey City NJ
  • 1990 K75S
Jersey City NJ
1990 K75S

Offline Laitch

  • Faster than a speeding pullet
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Re: My K75 restoration
« Reply #5 on: April 25, 2021, 11:20:19 PM »
. . . when I run it some fuel seems to squirt out of the top seam of the pump itself (In the tank) so Maybe it's not putting enough pressure to open the injectors??
Fuel pressure doesn't open the injectors; they're opened electronically. Cleaning all electrical connectors and ground connections asap with DeoxIT D5 is recommended.

Autozone, NAPA, or another of the large auto parts chains will loan you a pressure tester—or many other types of tools—if you use a credit card to make a refundable security deposit.


  • Along the Ridley in Vermont.
  • 1995 K75 89,000 miles

Offline The Mighty Gryphon

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Re: My K75 restoration
« Reply #6 on: April 26, 2021, 10:20:35 AM »
I don't have time to review your previous posts, but did you do anything to the injectors and the fuel rail?
  • 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 mcgyver74

  • Motobrick Curious
  • Posts: 24
Re: My K75 restoration
« Reply #7 on: April 26, 2021, 10:22:57 AM »
Have not touched them,  should I pull the injectors and give them a soak?
  • Jersey City NJ
  • 1990 K75S
Jersey City NJ
1990 K75S

Offline The Mighty Gryphon

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Re: My K75 restoration
« Reply #8 on: April 26, 2021, 10:27:23 AM »
Ummm... Judging from your tank, it could be a good idea.  You want to get o-rings and filters for them too. 

And don't forget the rail.  Vinegar is your friend there.  You might want to toss the fuel level float in with the rail, just for chuckles.
  • 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 mcgyver74

  • Motobrick Curious
  • Posts: 24
Re: My K75 restoration
« Reply #9 on: April 26, 2021, 10:32:46 AM »
can I soak the injectors in Vinegar? or is there a special solutin I should use?

I will get new O rings and I plan to replace the fuel filter,  thankfully I didn't try to use the rusty crusty tank, I bought a good used tank instead with new filter  :)
  • Jersey City NJ
  • 1990 K75S
Jersey City NJ
1990 K75S

Offline The Mighty Gryphon

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Re: My K75 restoration
« Reply #10 on: April 26, 2021, 11:13:31 AM »
Vinegar works best on rust and mineral buildup.  For the injectors use a fuel system cleaner after doing a good external cleaning with brake cleaner. 

After the soak, blow some spray cleaner through them with one of these kits:

https://www.ebay.com/itm/352819192943?hash=item5225a9a46f:g:Gq4AAOSwsgtfplAY

Instead of a battery, I hooked my injectors up to an old Lionel train transformer, a doorbell transformer will also work.  The transformer is nice because it cycles the injector 60 times a second while you spray the cleaner through it.  Pull the filter screen out of the injector before you do the spray, but after you clean the exterior of the injector.

Soak the rail in vinegar for a couple days, flush it well and blow it out with compressed air.  Any crap in it will wind up in the injectors if you don't do a good job cleaning it.
  • 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 mcgyver74

  • Motobrick Curious
  • Posts: 24
Re: My K75 restoration
« Reply #11 on: April 26, 2021, 11:43:02 AM »
Thanks I will take a look. can I just use a battery to pulse the injectors? or is it important to cycle them as they would be on the bike?
  • Jersey City NJ
  • 1990 K75S
Jersey City NJ
1990 K75S

Offline The Mighty Gryphon

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  • Posts: 6683
Re: My K75 restoration
« Reply #12 on: April 26, 2021, 11:52:28 AM »
A 9v battery is the normal way.  The transformer is the way I go if they're stuck closed.
  • 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 stokester

  • ^ SuperNatural Motobricker
  • Posts: 815
Re: My K75 restoration
« Reply #13 on: April 26, 2021, 05:49:58 PM »
If necessary - I've had good success with Mr. Injector
https://www.mrinjector.us/
  • Yorktown Virginia
  • '94 K75S Dakar Yellow - '93 K75S Seiden Blau - '91 R100RT Bermuda Blue- '78 R100S Smoke Red
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Offline mcgyver74

  • Motobrick Curious
  • Posts: 24
Re: My K75 restoration
« Reply #14 on: April 26, 2021, 09:43:02 PM »
I got a deal on refurbished injectors from beemer boneyard,  figured even if I clean them they are 30 years old  :)
  • Jersey City NJ
  • 1990 K75S
Jersey City NJ
1990 K75S

Offline Laitch

  • Faster than a speeding pullet
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Re: My K75 restoration
« Reply #15 on: April 27, 2021, 05:27:55 PM »
I got a deal on refurbished injectors from beemer boneyard,  figured even if I clean them they are 30 years old  :)
They could be thirty-year-old injectors that have been refurbished.  icon_cheers
  • Along the Ridley in Vermont.
  • 1995 K75 89,000 miles

Offline mcgyver74

  • Motobrick Curious
  • Posts: 24
Re: My K75 restoration
« Reply #16 on: May 01, 2021, 10:32:06 PM »
Well, this was a productive week :)

Finally installed the new Fuel pump (Don't have pics of that) and the new fuel lines and filter

Next thing to tackle was the breather hose that always fails,  and mine was no different,  Man that is roached



Shiny new one installed



At this point, the new pump is in, the lines and breather are in, so I tried to fire it up again.   No dice. Confirmed I have compression and spark so guess what is lacking is fuel.  Time to change the 30 year old Injectors :)

The first one came out pretty hard..  Had to use a pick to get the cap and O ring out :(  and the O rings were hard as a rock :(



After a bit of a fight, I got all 3 out :)



Next was to blow out the fuel rail,  luckily it was pretty clean inside..


Test fitting all 3 new injectors, (Before I realized it was easier to put them on the fuel rail before installing LOL)




Finally buttoned it up and SHE RUNS!!! (Not sure how to post a video so sorry for the youtube link)


Still hesitates off idle, not sure what that's about. but now that I know she runs I can order the brake parts I need..  Stay tuned for the next installment :)







  • Jersey City NJ
  • 1990 K75S
Jersey City NJ
1990 K75S

Offline The Mighty Gryphon

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Re: My K75 restoration
« Reply #17 on: May 01, 2021, 11:17:06 PM »
Nice work! 

About the hesitation, I have noticed that for some reason(I suspect it may be the inertia in the air flow flapper causing a momentarily lean mixture) my K75 engines like to have the throttle rolled on as opposed snapped open.  This temporary lean mixture was the reason for the accelerator pump on carburetors.  Unfortunately, the early Jetronic systems weren't able to instantaneously enrich the mixture when the throttle is quickly opened.

Throttle response off of idle seems to be better on the K100's and the Motronic engines.  I think the extra cylinder also helps overcome the inertia of the crankshaft as well as yanking the air flow flapper open quicker.
  • 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 TriSpark

  • ^ Motobrick Curious
  • Posts: 65
Re: My K75 restoration
« Reply #18 on: May 04, 2021, 06:52:44 PM »
Nice to see you got it running - what a great feeling that is when you revive an old bike. I have an '87 that I bought back to life a few years back with help from the guys here, and now it runs like a charm. Looking forward to your next video when you are able to ride it.
  • Chattanooga TN
  • Red 1987 K75s

Offline natalena

  • ^ SuperNatural Motobricker
  • Posts: 628
Re: My K75 restoration
« Reply #19 on: May 12, 2021, 12:06:08 AM »
Awesome work getting the brick running again. Good luck on finding a good tank, and on the other hand, the time waiting for the tank can be spent relubing the drive, flushing brakes and forks, etc. Enjoy, these bricks are fun to work on.
  • MST
  • 1987 K75s #0919, '05 Sportster 1200C, '21 ARGO 8x8, '24 KLR650
Texas catheters ROCK!

Offline frankenduck

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Re: My K75 restoration
« Reply #20 on: May 12, 2021, 12:31:53 AM »
Still hesitates off idle, not sure what that's about. but now that I know she runs I can order the brake parts I need..  Stay tuned for the next installment :)

I set the idle at 1150-1200ish on my K75s so that there's less hesitation when starting from a dead stop.
Once I had a Collie pup. Dug a hole and covered him up. Now I sit there by the hour. Waiting for a Collie-flower.
New to K bikes? Click here.
K Bike Maintenance & Mods: Click here.
Buy parts here.

Offline mcgyver74

  • Motobrick Curious
  • Posts: 24
Re: My K75 restoration
« Reply #21 on: June 07, 2021, 09:53:56 AM »
Sorry for the delay folks, was away for a while.   Got some work done over the weekend but it will still be a bit before she rolls down the road :).


This weekend was a slow weekend,  due to the heat, it was difficult to get a lot done but I did manage to replace all the front brake lines and flush some nice new brake fluid into the system.

Replaced all 3 front brake hoses with a kit from Speigler.  The job is not too bad but make sure you use a line wrench and not a regular wrench.

Once all 3 lines were replaced I bled the brakes, and this is where some oddness occurred... Was wondering if y'all encountered this before..

My process was as follows:

  • Sucked out the old cruddy fluid from the MC with a vac pump
  • Removed and reinstalled all 3 brake lines
  • Cleaned MC reservoir out with a towel to get most of the nasty out
  • Filled Res with new clean fluid
  • Cracked both bleeders and let it gravity bleed for a bit until new fluid was dribbling out of the bleeders
  • Closed left bleeder,  put vac pump on right bleeder and pulled fluid through until no bubbles were seen
  • Closed Right bleeder and repeated this process on left side


The VERY odd part was I had NO brake handle at all, I pulled almost a quart of fresh clean brake fluid through and had NO brake at all..(Yes the handle seemed fine prior to the work)  No air bubbles were present but it just would not firm up (had ZERO feel).

I finally got frustrated and needed some cold drinks, so I put the res cap back on and went to lunch, when I got back the handle felt normal again  :johnny  it literally went from nothing at all to normal feel on it's own.  this is making me VERY nervous...

Anybody ever see this before?

Sorry for the photos, it was hot as hell in the garage and I wasn't taking as many photos...








Next week I plan to tackle the following (Time and heat dependent)
  • Rear brake lines
  • Intake Manifolds and air boots
  • Gas Cap rebuild




  • Jersey City NJ
  • 1990 K75S
Jersey City NJ
1990 K75S

Offline frankenduck

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Re: My K75 restoration
« Reply #22 on: June 07, 2021, 10:12:49 AM »
"Gravity bleeding" (whatever the heck that is) does not do anything to get air out of the system.

When refilling the brake lines:

Turn the handlebars to full lock left.

SLOWLY squeeze the brake lever repeatedly while topping off the master cylinder reservoir as needed. You will see tiny air bubbles coming up as you do this. When the air bubbles stop you've gotten all of the air out of the lines.

Then bleed off any remaining air bubbles down at the calipers.

Remember to pump the lever a few times before going for a test ride.
Once I had a Collie pup. Dug a hole and covered him up. Now I sit there by the hour. Waiting for a Collie-flower.
New to K bikes? Click here.
K Bike Maintenance & Mods: Click here.
Buy parts here.

Offline Laitch

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Re: My K75 restoration
« Reply #23 on: June 07, 2021, 10:25:40 AM »
. . . it literally went from nothing at all to normal feel on it's own.  this is making me VERY nervous...
Anybody ever see this before?
Yes. Pressure can be lost when a closed system is opened.

My most fun example is when I was conveying myself in a '92 Honda 4x4 station wagon loaded with chainsaws, peaveys, log tongs and other esoteric material to help some friends whose home was covered in downed trees and debris in Miami three days after Hurricane Andrew. I was on the Cross-Bronx Expressway on the Friday of Memorial Day weekend in traffic that was alternating between 50mph and Omph when my brake pedal went to the floor. I hauled up on the emergency brake between the seats then used it to brake and shift with one hand, and steer with the other hand for a few exciting miles, crossing the GW Bridge and final exiting in a New Jersey rest stop. I left the vehicle and had a cup of coffee and a piece of pie in the restaurant while I considered my options.

My option was to find help on a holiday weekend in the Capital Region of Grift or do something else. I decided I'd make it to Miami using the hand brake and get there one way or the other. After I finished eating, I went to the car, opened the hood and there was the master brake cylinder's cap just resting on the threads of its reservoir. I bought some fluid to top up the level, screwed on the cap tightly, started the engine, took a deep breath then stepped on the peddle. It went down about halfway and came up to normal when I pressed it again.

The brakes worked well for years after that; it was the body rust from highway snow removal that wrecked the car.
  • Along the Ridley in Vermont.
  • 1995 K75 89,000 miles

Offline mcgyver74

  • Motobrick Curious
  • Posts: 24
Re: My K75 restoration
« Reply #24 on: June 07, 2021, 10:30:56 AM »
"Gravity bleeding" (whatever the heck that is) does not do anything to get air out of the system.


Yeah, that does not get rid of the air totally, but it actually does speed up the bleeding process, it lets fluid make its way down the lines so that when you do a normal bleeding procedure it 's a lot less air to pull out.

I've bled brakes using the pump method before, works well, but I switched to a vacuum pump method years ago since I am lazy :)
  • Jersey City NJ
  • 1990 K75S
Jersey City NJ
1990 K75S

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