92 k75s and a particularly dumb idea

[Kt88]

I’m a serial monogamist when it comes to motorcycles. I’ll only keep one at a time, and I’ll pour my myself into it, but when a new project catches my eye- well, the heart wants what the heart wants.

I’d just sold my 71 r75/5 after bringing it back from a circa 1980 slumber, having ridden it around for a year or so.

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Lo and behold, delivered to my eyes was my next obsession: a derelict k75 down in the Florida Keys.

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Now, other life occurrences meant I have a shoestring budget (good for a derelict k75), no truck (bad for a derelict k75), and about a day to make this all come together. Compounding my sense of urgency, this bike was priced as if it weren’t in South Florida, where there’s got to be some rust tax that adds 1k to every asking price for some reason I’ve yet to fathom.

So the plan, as dumb as it is, is to go down and rouse the machine and.. ride it back. It’s only 80 miles, what could go wrong?

My better half and pup go down with me and my trunk of tools. Upon arrival, I recognize that pictures were kind, and salt air isn’t. Everything is crusty and rubber is a flimsy concept rather than a pliable material. If it were easy, though, it’d not be an adventure, right? ..at least that’s what I told my wife as she watched this calamity unfold.

All told, major items that were kaput:
Fuel pump and filter (expected)
Sending unit (was hoping it wouldn’t have lost continuity but.. darn)
Front master cylinder (frozen dry and filled with powder)
Front tire (valve stem rotten)
Rear shock frozen upon first compression
All keyed cylinders frozen (one key only, better be gentle)

New battery, drained and flushed tank, but old fuel pump was unsalvageable. The auto parts stores down in the keys could get a Bosch pump that crossed over part numbers, but they.. forgot to put it on the truck when I ordered it. I cobbled together a pump, sock, and wiring from a Chevy application that had similar gph ratings and was on hand- I’ll go stock once I have parts in hand.  The sender unit solder had let go, so for the moment, I am powering the pump from the four pin connector to wires coming in through the gas cap. Very classy!


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Once the pump was pumping upon turnover, I verified we had spark (strong), and cranked. No dice yet. Pulled the fuel rail, sprayed off the ends of the injectors, then reassembled to a bunch of new little rail leaks from old o-rings. A couple washers on the rail to increase the pressure on the o-rings later, we have seals, and magically, we have engine life.

The rear brake bled out well, relatively speaking. The front MC will need complete rehab- at this point, it’s Sir Not Appearing In This Film. However, it’s worth noting that after a year of r75/5 riding, my braking distances mentally are measured in half miles anyway.

The front tire isn’t holding pressure. Upon examination, the valve stem is leaky around the seal. I’ll clearly get new tires, but to get home I use self sealing silicone tape around the stem. Probably one of the most willfully moronic things I’ve ever done, and surely I won’t repeat that choice.

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I replaced all the fuel lines, the overflow reservoir line, and hit the magic button. Off we went. Wife following me, we took our sweet time and turned an 80 mile trip into a 2.5 hour amble (then again, the Keys are generally 45 mph, so it wouldn’t have been terribly different under normal circumstances, either)

After exactly no real drama, other than some fueling misbehavior at the very end of the ride after an hour of freeway, the bike is in its new home, safe and sound. And the process of correcting hack mechanic work and the ravages of time begins.

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Now for the fun: disconnecting the 90s era alarm system (titan 3003), identifying another clear PCB accessory wired in with no brand name of any kind, returning stock functionality in all systems, and cosmetically freshening the bike up.

I’m not into modifying bikes these days- I’ll keep it stock as appropriate, with possible suspension upgrades.

One note, and maybe I’m preaching to the choir:
Coming from airheads (I’ve had about 35 or so), I’ve always been told a k75 is a great engined bike, but has no character. Riding back under very far from ideal circumstances last night, I didn’t feel that way at all. I would have screamed for joy for my R bikes to run as smoothly as this abandoned k75 did last night. I would have started threads on ADV detailing how I got there. I’d have written novels about the smooth tractability of the power. Do people just not like the K architecture as much? The frame felt great, and I had NO rear suspension. I can only imagine how much more I’ll love it with actual function.  Is this me having rose colored glasses on because I moved from a bike built in 71 to one built in 91?

Anyway. I’m currently in love and can’t wait to make the bike fully functional, safe, and a daily again.

[Chaos]

Great story, kudos for not trailering it or giving up.  I always thought the K75s had character, the smoking start ups, extreme side stand lean angle, stock windshield that basically just generates noise, mine even fouled a plug occasionally. Imagine if it were perfect how boring it would be.

[Kt88]

Ha, thanks. The to do list that beckons once I’m through with work today:

Replace front valve stem
(Maybe) boil front master cylinder to try and free it up?
(If there’s time) take rear shock off to see if I can make it, I dunno, move at all?
(Definitely not today, maybe tomorrow) go get new injector o-rings so I can stop using extra washers to seal the rail- as the extra washers that were on hand were in fact actually cabinet corner hardware and not even kind of inconspicuous.

[The Mighty Gryphon]

Great story!  Sounds like an episode of Roadworthy Rescues.  I have had two K75's an RT and an S like yours.

I think the problem with the Bricks is that the traditionalist airhead/boxer fans have spent nearly 40 years bad-mouthing them.  I have found mine to be super reliable, bulletproof and capable of running 85+mph smoothly for as many 800 mile days as I could handle.  They are great Iron Butt machines.  I have easily kept up with and even pushed guys riding 1000 and 1200cc machines on the interstate as well as the mountains.

They are cheap for what you get, easy to work on, and parts are still easy and not too expensive to find. 

[Kt88]

Replying while trying to re-seat a bead at home sans compressor on rock hard sidewalls:

I think there’s also some aversion amongst the airhead-only guys to really rev these. Despite being told for years that my type 247s could live just fine at 5k+, I tended to still cruise around 4500.  So for the most part the enjoyable bit of the engine was low speed torque.

Now keep in mind 90% of my riding with this is with a flat front tire (sweet lord I’m a moron), but my feeling is this will take mildly more clutch work and much more revs to find the happiest point for the drivetrain. I’m fine with that. I think I’ve definitely put enough time in on the R twins to have a good idea about the attractive parts to those bikes, and I’m mostly excited to figure out new things to love about these.

Now to check on the tire, suspended above a boiling master cylinder- hopefully it will become pliable enough to seat the bead with a ratchet strap and foot pump, as that’s what I’ve got.

[Laitch]

Coming from airheads (I’ve had about 35 or so), I’ve always been told a k75 is a great engined bike, but has no character. Riding back under very far from ideal circumstances last night, I didn’t feel that way at all. I would have screamed for joy for my R bikes to run as smoothly as this abandoned k75 did last night. I would have started threads on ADV detailing how I got there. I’d have written novels about the smooth tractability of the power. Do people just not like the K architecture as much? The frame felt great, and I had NO rear suspension. I can only imagine how much more I’ll love it with actual function.  Is this me having rose colored glasses on because I moved from a bike built in 71 to one built in 91?

Sounds like you're in the honeymoon phase. Keep up with the candy and flowers. 

Good luck with your Brick.

[The Mighty Gryphon]

Sounds like you're making progress on your brick.

Have you ever tried putting a little propane or starting ether in the tire and lighting it off with a bunch of soapy water on the beads?  Boom.

The 75 has a pretty decent power band with usable torque from about 2500rpm for city riding.  When I first got mine, I was constantly fishing around for 6th gear.  Then, after a year and 10,000 miles I found myself riding on the interstate at 65-70 in 4th gear.  The classic K engine loves to rev.  I have heard that it has been tested running at redline under full load for 24 hours.  That translates to around 2700 miles in one day.  I know that I was able to do 1500 miles in one day on a fully loaded K75RT that had 85,000 miles on it.

[caveman]

Kt88,
I got my 75s just to go on day rides. I felt like a moron riding a touring bike for a day or weekend ride. Long story short it is my go to outfit and has bin cross country several times. Please keep us posted on the progress with your bike.

[Laitch]

Have you ever tried putting a little propane or starting ether in the tire and lighting it off with a bunch of soapy water on the beads?  Boom.

Here's an educational video with a compelling soundtrack to clarify the process, Kt.

[Kt88]

Here's an educational video with a compelling soundtrack to clarify the process, Kt.

So you’re telling me I shouldn’t use a tractor/trailer rim setup? Pretty disappointed in that news.

In a previous life I was a tire tech (ah, the early 20s) and I still never did the old farmer’s trick of exploding a tire onto a rim. Working out of a big shared apartment garage I’ll probably try to keep the explosions inside the cylinder walls and wait until someone with a compressor is open around me , and try to seat it the old fashioned way. I’m only keeping this tire on long enough to have new ones mounted at a buddy’s shop- but that’s an hour and a half north of here.


In other news, three hours of boiling the master cylinder did.. nothing at all. So I’ll be sourcing a replacement, which is probably a better bet anyway.

In better news, the bike fires immediately on the center stand right now, no hesitation. That’s promising.
The water temp indicator is still illuminating while running, but I’ve not traced that circuit at all.

Shopping list as of now (to be executed once there’s budget for it):
Front MC
Rear Shock
Sending unit (tempted by the 17$ two wire one I saw another inmate post about, even if it’s temporary)
Injector seals
Then just work through the rubber bits little by little.

When I have the rear wheel off for the new tire I’ll do my due diligence on the splines. I don’t think pulling this transmission looks any harder than an airhead transmission. 

[frankenduck]

Send the injectors to: https://www.mrinjector.us/

Metal valve stems: BikeMaster 151402

The K75's "character" is all above 4,500+ RPM. Run through the full range up to the rev limiter at 8,700 RPM. You'll have peak torque a little under 7,000 RPM. (Bouncing off of the rev limiter won't hurt it.)

[Kt88]

Send the injectors to: https://www.mrinjector.us/

Metal valve stems: BikeMaster 151402

The K75's "character" is all above 4,500+ RPM. Run through the full range up to the rev limiter at 8,700 RPM. You'll have peak torque a little under 7,000 RPM. (Bouncing off of the rev limiter won't hurt it.)

New valve stem in, just ancient rock hard rubber trying to bead seat with a foot pump isn’t likely.

Duck, to be honest, when building the fascination for the k75 in my head I ran across about a thousand posts of yours on ADV and they probably have a lot to do with pushing me over the edge to the point of purchase.  Thanks for that!

[frankenduck]

Here's my New to K Bikes web page: http://bit.ly/new2kbikes

And a bunch more K bike stuff: http://bit.ly/kbikemandm

[Kt88]

Master cylinder freed up after boiling and some percussive therapy. Getting some action at the abs modulator, but there’s a lot of dry line between there and the calipers up front. I think I’ll make a vacuum bleeder today to speed that up.

Front wheel is back on with the old rubber, just waiting until I can get fresh tires to put on it.

My luck may have run out with my for-retrieval-only fuel delivery situation. The bike will start but won’t take throttle at all, but I’m not actually upset at that. It’s time to dump all fluids and change all filters anyway, and the pump situation in the tank was always meant to be temporary. If anything, this will force me to get the rest of the braking situation settled before I get carried away with test rides. 

After a few days of penetrant soaking the bag locks are finally behaving like they should. Key is turning easier in ignition also. It’s almost like the bike really wants to be alive!

[ErikDK]

Riding my K75RT at low revs gives me some flashback to riding my 1981 R100RS in 1996. I do miss the torque, though.

A hi/lo lever like the Honda CB750 C would be awesome on the K75, or even better an electric operated under/overdrive

[Kt88]

Managed to re solder pump supply wires through the sender, so now nobody would be the wiser from the outside that the fuel delivery system has been hastily replaced.

The front master cylinder, while freely moving, is not holding pressure- or even generating it, for that matter, just bubbles- so I’m now shopping for one in usable shape or at the minimum worthy of a rebuild kit.

I’ve started replacing bulbs to get the bulb indicator light to relax a little upon startup. Those connections still seem pretty intact, but the PO’s alarm system is tied into almost every single part, including all the marker/blinkers. I’m a bit hesitant to just start pulling it since I imagine it’s protected against that method somehow, but I will absolutely do it before any big miles.

Once the front brakes are happy, then it’s time for new tires- open to recommendations there- full spline service, and flushing all fluids stem to stern.

Oh, and the plastic fairing support is cracked all the way through. It’s held together with tape at the moment. I’ll replace that, too.
 
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[frankenduck]

Radial tires are the way to go for 3-spoke wheels:
http://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/radials/radials.htm

[Kt88]

That’s an awesome write up. Thank you so much!

[stokester]

Great rescue story.

I like riding my Airheads and K75s as they both have their own character.

You've come to the right place for information and recommendations.

Keep us updated on your progress.

Nick

[Kt88]

All is humming along pleasantly on the low budget rehabilitation of the bike. An interesting thing is holding my attention right now: the temp sensor light is constantly lit, but the coolant seems to be circulating, the fan cycles what I believe to be normally (on and off in about 30 second to 1 minute bursts when in traffic after running the bike for a bit), and plugs/exhaust/running all seem pretty normal. Overflow tank has coolant about halfway up the line.

I’ve read a lot of threads about flickering or worry that the light doesn’t illuminate at all, but it’s been solidly on since the engine ran for the first time in my possession. If the key is on, the light is on.

Figured I’d ask the brain trust here- it seems to me that if the sensor wasn’t functioning at all or was always in low resistance mode, I’d have light on/fan on constantly. The fan seemingly operating as it should is interesting. There’s always the possibility that the temp light has been futzed with and incorporated into the alarm system (non op, thankfully) and it’s representing that now, but I’d hope not.

[The Mighty Gryphon]

If everything temperature related is working properly, ie. the fan cycles properly, the cooling system isn't overheating and the engine isn't running on a bad mixture, then I would think the problem is in the temperature module, the instrument cluster, or possibly a wire with worn insulation shorting to a bare spot on the frame.

First thing I would do is pull the temperature module and see if the light goes out.  If the light stays on, the problem may be in the instrument cluster.  If it goes out I would suspect the temperature module.  Next thing would be to see if you can get a module to swap with the one on the bike for a positive test. 

[frankenduck]

If everything temperature related is working properly, ie. the fan cycles properly, the cooling system isn't overheating and the engine isn't running on a bad mixture, then I would think the problem is in the temperature module, the instrument cluster, or possibly a wire with worn insulation shorting to a bare spot on the frame.

First thing I would do is pull the temperature module and see if the light goes out.  If the light stays on, the problem may be in the instrument cluster.  If it goes out I would suspect the temperature module.  Next thing would be to see if you can get a module to swap with the one on the bike for a positive test.

Yeah, if it's running well and fan cycles as it should with the temp idiot light always on then I'd also suspect something funky with the thermo relay. (The white one on the right side of the relay box.)

Another possible cause for the temp idiot always on is that the VIO/BLK wire from the temp relay (Pin A3) is shorting to ground somewhere between the temp relay and cluster.

When you have the temp relay pulled the idiot light should come on if you ground the socket terminal for the A3 pin - with ignition turned on. (Pin layout is shown on the temp relay.)

[Kt88]

Finally had a little more time today. I’d previously gotten a used but nice master cylinder (actually, whole right control unit) for the front brakes sent to me but had yet to be in town to install it. After a quick wipe down the new MC was installed into the controls on the bars (no need to switch everything over yet, all else is functional) and rather immediately developed pressure my original one couldn’t muster. The ABS unit bled quickly and had strong pressure. I moved to the next bleeder valve, at the left front caliper next, and there was absolutely nothing happening of any kind. Over the next two hours I worked my way piece by piece back until I was at the hardline coming out of the ABS module- great pressure there, nothing once it went to the soft line that actually runs to the calipers. I investigated the line and felt it was likely blocked with old residue and not allowing any fluid to pass. A quick exploratory poke through the line with a clothes hangar snipped into a probe revealed I was right and gentle prodding cleared a bunch of rust colored trash out. After that the system bled very quickly and easily and let me tell you, dual brembos are a heck of a lot more potent than the r75/5 drum I’m used to. Nice! ABS unit pulsed nicely on lockup, bike stops very, very quickly in the parking lot. I am thrilled.

I also got my Mr. Injector kit in and refreshed the injectors and got the fuel rail seated happily. Bike is purring like a kitten.

Replaced bulbs out of their economy and to lay eyes on all the sockets. For the most part healthy, minus some dessicated o rings that seal up the socket areas in the fairing. I’ll replace those too.

At this point I have a few tasks ahead to feel great about the bike altogether:

Change rear pads
Change tires
Fork seals/general internal condition inspection
Rebuild works rear shock
Refresh engine cosmetics
Fit belly pan (previous owner found it after swearing he’d never seen it in his life)
Flush fluids and investigate splines, various bearings
Repair or replace central fairing support
Find source of bulb monitor light warning
Find source of temp warning
Clean up existing paintwork and refresh frame and control cosmetics
Replace control cables


Finally-
Ride it a whole lot

Enjoying the heck out of this whole process! Thanks for all the info and support. Once I’m not working in a dark corner of a parking garage I’ll share some progress pictures.

[Kt88]

One of the nicer bits about living in Miami is that I essentially have year-round riding. Does wonders for seasonal depression, but also does make every project a living one, as opposed to a winter disassembly as I’m used to.

Nevertheless, I’m persisting. It’s awfully rough on me, as you can probably tell.

Tags came in yesterday, and using the bike as my primary transport is now underway officially.

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I’ve got some more cosmetic cleanup to do on the old headlight glass (yellowed and foggy), the fairing attachment, and the glazed windshield. I may use this to justify buying a random orbital buffer.

[Laitch]

One of the nicer bits about living in Miami is that I essentially have year-round riding.

Riding through summer afternoon squalls from the Big Cypress rolling over South Dixie Highway in Kendall while dodging flying palm fronds, broken tree limbs and assorted leaf litter was especially nice.