K75S / 1988 Bringing back to life

[NomadZen]

Hi everyone, new member here.
I normally ride R NineT but was looking to work on a project and couldn't pass on a seemingly great deal and got myself BMW K75S 1988 as pictured:



Bike was sitting for 6 years and owner doesn't know the history, no keys, no battery, no documents (bike was abandoned by it's owner and sold by the property owner).
I was able to turn it on recently, after replacing alternator that was shorted to ground and did a regular maintenance (oil, spark plugs, lubed final drive spline, put a new tires, etc).

I haven't able to find a cause of particular issues with the engine yet, and there are two so far:
1. engine halts if I try to throttle fast enough
2. sometimes there's banging noise in the engine that concerns me, not sure if this is a problem or not

I made a video that demonstrates those issues and if someone have ideas,
I'd be grateful

.

Regards and keep the rubber down everyone!

 

[98lee]

Magomed,

Was the engine warmed up prior to shooting your video?

The idle sounds a little low. Noticed the tach is not working. You might want to check that. You want the hot idle between 1000 and 1050, Not the 950 that the book says.

If the engine was warm, than I would suspect a vacuum leak. Check these possible sources of vacuum leak: cracks in crankcase vent hose, cracks in rubber manifolds above and below throttlebodies, cracked or misseated large 90 degree hose between airflow meter and intake plenum, o-ring on oil fill cap, tank vent hose between tank and crankcase either cracked, not properly connected or capped.

Many other possible causes, but I would check these first.

 

[lee]

Lee, should he replace the fuel pump rubber damper, or check it before running the engine more?

Welcome to the site Mogomed.
Where are you located?

 

[98lee]

Lee, should he replace the fuel pump rubber damper, or check it before running the engine more?

Welcome to the site Mogomed.
Where are you located?

Lee,

Absolutely! I have a bad habit of assuming that the known things have already been checked. But, people new to Bricks don’t know the known things. Opps.

Mogomed,

If the bike has sat for a long period with fuel in the tank, odds are that the bad fuel has attacked the rubber fuel pump mounting collar. When that rubber breaks down, it settles to the bottom just below the fuel pump intake. Then, years later, someone comes along and decides they are going to try to start it. They throw in a battery and maybe put fresh gas in it. First thing that happens is the fuel pump sucks up the dissolved rubber into the pump, then the filter, and possibly past the filter and into the injectors.

Would be a standard procedure to pull the pump, inspect/clean inside of tank with extra attention to the well below the pump. Inspect/replace pump rubber mount (should have firm consistency like a tire and not leave any black on your fingers while the mount is still wet with fuel. Definitely replace filter! Possibly replace fuel hoses in tank (use SUBMERSIBLE FUEL INJECTION hose ONLY!!!). Probably replace pump pickup screen and screen vent hose (I’ve only found this hose from BMW). Possibly replace pump.

It would be a good idea to send out your injectors to Mr. Injector in Cours d’Alene Idaho and have them refurbished (very reasonably priced).

Once the fuel system is clean/functioning properly, TEE a pressure gage into the line at the rear of the fuel rail (must be tee’d in so that the pressure regulator is still in the circuit!). You should have 38psi while the engine is running.

If it doesn’t run right, check the vacuum stuff, then let us know.

 

[lee]

Thanks 98lee. I knew you would give better instructions then I could.

 

[NomadZen]

Thank you all, those are really good advice.
I have already done some - replaced fuel lines (including the one in the tank), fuel filter.
I didn't check the pump itself and going to do that.
If I have 38psi, can I assume that pump and fuel system is fine?

 

[pglaves]

Thank you all, those are really good advice.
I have already done some - replaced fuel lines (including the one in the tank), fuel filter.
I didn't check the pump itself and going to do that.
If I have 38psi, can I assume that pump and fuel system is fine?

Probably. The issue is the rubber damper that the pump mounts in. They dissolve in ethanol fuel. If it feels like a tire you are OK. If it feels like a marshmallow replace it. If it sticks to your finger when you poke it, it is really bad and needs to be removed immediately before the drippings clog everything.

 

[98lee]

I’ve started using Quantum pumps and install kits from highflowfuel.com https://www.highflowfuel.com/qfs-fu...ooter-efi-in-tank-oem-replacement-hfp-437-tf/

Everything looks good, great price and lifetime warranty!
No long term experience yet. Time (and miles) will tell.

 

[k547]

@98lee

Wow! I wasn't aware of Quantum's fuel products until I saw your post.
I looked and they have 7 various fuel pump "kits" for my '03 K1200RS with the most expensive/complete priced at $99.98!! (if it cost 2 cents more it would qualify for 10% discount).
Compare that to my favorite vendor in Colorado with a slightly more complete "kit" (I optioned it with new hose clamps and fuel float gasket) at $356.50.
That's a whopping $256.52 price difference (before tax and shipping of course, which I didn't factor in).
That's really tempting to just buy and put on the shelf for later... It just tortures me seeing such a good price like that.
I have this vision of taking the time and effort to install and then having an early failure and all just because of the low price, but in reality for all I know it could be better quality than the higher priced unit....or not.....
Sure is tempting....

 

[k547]

@NomadZen

I don't mean to hijack your post.
That looks like a really rewarding project and I look forward to following your progress here.
A close friend of a good friend of mine had a K75S that I wanted badly and I said several times I'd pay his asking price when he sold it.
But after a couple years he sold it to a stranger without telling me.
Something with these two, when they sell a bike (their bikes are all very high quality examples) they want it "to go away" and don't want to see or hear about it after the sale. IE no "friends" sales.
Very frustrating for me....

 

[98lee]

@98lee

Wow! I wasn't aware of Quantum's fuel products until I saw your post.
I looked and they have 7 various fuel pump "kits" for my '03 K1200RS with the most expensive/complete priced at $99.98!! (if it cost 2 cents more it would qualify for 10% discount).

I just added this to the order and ended up with a handy liquid filled fuel pressure gauge for less than $5.

QFS EFI Liquid Filled Fuel Pressure Gauge (Choose Style)

FREE SHIPPING, LIFETIME WARRANTY from the AUTHORITY on OEM replacement Fuel Pumps. SAVE up to 70% off on parts for your vehicle. Shop HFP-FPG-100,HFP-FPG-100-B,HFP-FPG-100-W

www.highflowfuel.com

The 0-100 white one is better suited to the range we need and it’s cheaper!

 

[NomadZen]

Hey all, just wanted to update on this, I did order some of the things, Quantum pump and their mano, cabrsync tool but haven't got to that part yet.
Rubber damper seems fine to me, it feels like a regular rubber, just a bit squishy -- will replace it anyways probably along with the fuel pump but want to confirm the issue first.

I measured fuel pressure and it seems fine to me at 36 PSI when running, also keeps up after bike is off so I assume pressure it's good.



That said, I see cracks in throttle bodies, so I suspect it's the main reason of issue:



I've got the throttle bodies from EME but haven't got clamps that are seems to be single use, will be looking for them and then will replace.

Another potential issue I'm looking at is one of the injectors seems to be in a worse condition comparing to others, it's yellowish near the contact:


Next things I'll be working on:
- change throttle bodies
- tune idle with carbsync
- check valves, I don't expect them to be out of specs as bike only has 19k miles

I looked into the my speedo and the board seems fried and rusty, probably water went inside, so I'm thinking to throw it away and install Acewell speedo + BEP3 instead.
Anyone have hints on how to measure idle RPMs without speedo?

 

[NomadZen]

@NomadZen

I don't mean to hijack your post.
That looks like a really rewarding project and I look forward to following your progress here.
A close friend of a good friend of mine had a K75S that I wanted badly and I said several times I'd pay his asking price when he sold it.
But after a couple years he sold it to a stranger without telling me.
Something with these two, when they sell a bike (their bikes are all very high quality examples) they want it "to go away" and don't want to see or hear about it after the sale. IE no "friends" sales.
Very frustrating for me....

Thank you and no worries, I'm really looking forward to fix the bike. At this point I've spent on tools, parts and fees to register so much, I could have got properly running bike lol.
One thing is I can't make my mind to either strip it and customize vs restore to how it is with fairing.

 

[98lee]

Hey all, just wanted to update on this, I did order some of the things, Quantum pump and their mano, cabrsync tool but haven't got to that part yet.
Rubber damper seems fine to me, it feels like a regular rubber, just a bit squishy -- will replace it anyways probably along with the fuel pump but want to confirm the issue first.

I measured fuel pressure and it seems fine to me at 36 PSI when running, also keeps up after bike is off so I assume pressure it's good.

View attachment 96866

That said, I see cracks in throttle bodies, so I suspect it's the main reason of issue:

View attachment 96867

I've got the throttle bodies from EME but haven't got clamps that are seems to be single use, will be looking for them and then will replace.

Another potential issue I'm looking at is one of the injectors seems to be in a worse condition comparing to others, it's yellowish near the contact:
View attachment 96868

Next things I'll be working on:
- change throttle bodies
- tune idle with carbsync
- check valves, I don't expect them to be out of specs as bike only has 19k miles

I looked into the my speedo and the board seems fried and rusty, probably water went inside, so I'm thinking to throw it away and install Acewell speedo + BEP3 instead.
Anyone have hints on how to measure idle RPMs without speedo?

Nomad,

Damper should not be “squishy”. Damper that comes with Quantum pump kit is ethanol resistant.

Fuel tank is aluminum (don’t buy a magnetic tankbag ), so the inside should be bright silver. A brownish tinge indicates a dissolving damper.

A solid steady 36psi on the gauge is within the margin of error.

Yep, those rubber manifolds need replacing. https://www.euromotoelectrics.com/category-s/3238.htm
They have the clamps and the crimping tool too. If, like you implied, they are out of the clamps, you can order them from BMW for $25 for all 6.

Send your injectors to Mr Injector. https://www.mrinjector.us/ They’ll be back before you get the manifolds replaced. Don’t forget to blow all the sand and crap from around the base of the injectors BEFORE you remove them so it doesn’t get in the engine.

Do manifolds. Carefully inspect the large 90 degree rubber elbow between air filter box and intake plenum, replace crankcase vent hose, inspect/replace vacuum caps on #1 & #2 throttlebodies.

Check valves BEFORE balancing throttlebodies as valve adjust can greatly affect throttle balance.

Then balance throttlebodies. DO NOT MESS WITH THE HEADLESS SCREWS on the linkage between the throttlebodies. Only adjust the brass air bypass screws at the base of each throttlebody and the large head idle screw between #1 and #2 throttlebody. 1050 rpm..

 

[NomadZen]

Thank you! Those are all on my list, but you've got details I wouldn't think about Gotta write all down and go step by step.

Your link also has Airbox Manifold https://www.euromotoelectrics.com/product-p/manifold563.htm - I wonder if it normally needs replacement too?

 

[52184]

Necessary only if it’s cracked. Leaks between the air accumulator and the injector body will let in contamination but not directly affect mixture or running. The critical junctures are from injector bodies down to the head, plus the hoses and caps Lee has outlined for you.

In tanks that have the yellow-brown layer from dissolving rubber I’ve used a moderate-pressure washer to remove most of it, so it can’t go in suspension and create injector issues down the road.

Best,
DeVern

 

[98lee]

Nomad,

I strongly suggest that you do not use the Acewell speedometer.

Both people that I know that installed Acewells on their K75s went through all kinds of grief trying to get them working properly with their bikes.

You wil loose a bunch of functions going away from the factory dash incluning:

Self canceling turn indicators

Rear bulb monitoring (brake and tail)

Choke on light

Clock

Low fuel light

The gear indicator on the Acewell is poor because it calculates what gear you are in based on Rpm and speed. Entirely useless when you are stopped at a light and you want to be sure it’s in 1st before you take off.

Reseting the trip odometer while riding in areas where you need to pay attention to traffic or the road is not simple.

It is smaller than your speedometer or your tachometer with a bunch of info on it so it is not easy to just glance down and easily get all the info like you can on the factory dash



The right side of your bike appears in good condition. If the other side doesn't have any/much damage, that paint will polish (NOT rubbing compound) up really nice. I have a really good product for that. The paint on your bike is a high solid Glasurit single stage (no clear) so it takes a bit of polishing every few years to get rid of the oxidation, but it comes back like new.

The fairing on the S is a good compromise between too much protection (K75RT) that is uncomfortably hot in the summer and a naked bike that puts so much wind on your chest that you spend energy trying not to get blown back in the saddle with a death grip on the bars as you near (or pass) the century mark.

My suggestion would be get it running properly, clean it up and ride it for a season, get to know it, and THEN decide what you really want to do.

As far as the instrument cluster, there is currently one on ebay for IIRC $85 with a cracked lens. You have a good lens, so buy it and swap the cover. 9 screws to loosen the cover, pull the reset knob out (about 1/4”) to compress the spring and the cover comes off. Swap covers, plug it back in and go.

There are a couple clusters that are cheaper advertised for parts (they don’t work fully). Some have needles that aren’t pointing to zero. You don’t want those.

You don’t want the ones from Canada. KPH vs MPH

You don’t want one that has the gas pump emblem next to BOTH lights under the speedo, onlythe right hand one.

You do want one that has the choke symbol next to the yellow light below the tachometer.

You do not want one that has white horizontal lines across the lower half of the tach and speedo.

You want one that suggests it works. That way you can return it if it doesn’t.

That one for $85 in Santa Barbara looked like a good deal since you have a good cover/ lens.


Just saw this other one from the same seller on Ebay without a cracked lens. So just install and go.

BMW Instrument Cluster K75 K100, K100LT, K100RT, K100RS, K75 62112305252 | eBay

Here for purchase is a used Instrument Cluster for the BMW K-bike series. Part number is 62 11 2 305 252. All electronics believed to be working. Mileage unknown. This fits 1985-on K100,K100LT, K100RS, K100RT and will fit K75 models up to 07-1993. <br>

www.ebay.com

It is also the newer version with the Gortex vents on the back.

 

[98lee]

Necessary only if it’s cracked. Leaks between the air accumulator and the injector body will let in contamination but not directly affect mixture or running. The critical junctures are from injector bodies down to the head, plus the hoses and caps Lee has outlined for you.



Best,
DeVern

DeVern,

On the 2v K100 and the K75 that is not the case. The air flow meter is in the air cleaner box, upstream of that hose. ANY air that is introduced downstream of the airflow meter is not seen by the computer. There is no O2 sensor to allow for compensating for that extra air so it runs lean and it doesn’t know it. That is why ANY air/vacuum leaks on early Ks will make them run poorly or not at all.

 

[52184]

DeVern,

On the 2v K100 and the K75 that is not the case. The air flow meter is in the air cleaner box, upstream of that hose. ANY air that is introduced downstream of the airflow meter is not seen by the computer. There is no O2 sensor to allow for compensating for that extra air so it runs lean and it doesn’t know it. That is why ANY air/vacuum leaks on early Ks will make them run poorly or not at all.

Lee;
Thank you for the correction! I forgot about the MAF and I shouldn’t have as sticky ones were a problem on the early 2v K bikes. My bad!

Best,
DeVern

 

[98lee]

Lee;
Thank you for the correction! I forgot about the MAF and I shouldn’t have as sticky ones were a problem on the early 2v K bikes. My bad!

Best,
DeVern

DeVern,


You mean you don’t remember EVERYTHING???

I remember everything I ever learned about….. about…..uhh… what were we talking about??