I bought this 1987 K75C off a mate as a restoration project and for this year's Scrapheap Adventure Ride. Non-goer of course, in fact nothing worked but it would turn over if the starter solenoid was shorted across the terminals.


Nothing seemed to be too far wrong so I set about disconnecting and reconnecting things. This worked, it turns over, has lights etc and spark. Radiator has a pinhole but I've got another one coming so all good there.

Next step was to get it to run. New el-cheapo injectors from our friends in China ($48 for a set of 6). Still wont go. Sit and have a look for a while. Aha - spark plug leads are the wrong way around. Fix that and it goes - sort of. Its running on about 2 1/2 cylinders. No. 1 sort of backfires to the point that I can see flame around the intake where the arrow is on the photo below. The rubber is split which probably doesnt help. I'm wondering if the intake valve on this cylinder is sticking a little and not closing fully. It seems to run ok at around 2000-5000 but that might be an illusion. Any suggestions??

Check valve clearance, normally it wears bery slowly but has to be adjusted every 100 000 kms...
It won't run smoothly if the intake rubbers are worn. Same thing for the S rubber pipe between intake and coils.

I should have mentioned - it has 85k km on the odo. Based on the general condition, I'd say that's about right. The plan is to dismantle the thing and do a resto so many things will get fixed or adjusted as I go, including the valve clearances.

jbt wrote:It won't run smoothly if the intake rubbers are worn. Same thing for the S rubber pipe between intake and coils.

jbt, excellent suggestion.

Rockman, you might ask why?
Our bricks are ageing, regardless if you run them /high mileage/or let them standing in a barn /low mileage/.
So does the rubber.

After 35 years, it is not too bad an idea to replace all the rubber parts on the intake side.
Everything is still available /afaik/.
Good luck and lots of success

Yet another one Phil   ? 

Good onya 
Hopefully will come together for you eh ?

charlie99 wrote:Yet another one Phil   ? 

Good onya 
Hopefully will come together for you eh ?

Yep, bad dose of K Pox as I've had over a dozen of them so far. This one will be ok in the end. Pull it apart, find out what isnt right, then put it back together. Simple..

It will never run right. You bought a bike that was designed and built in the northern hemisphere. The fuel molecules will always spin in the wrong direction (like your toilets) resulting in suboptimal performance.

duck wrote:It will never run right. You bought a bike that was designed and built in the northern hemisphere. The fuel molecules will always spin in the wrong direction (like your toilets) resulting in suboptimal performance.

I'll ride it backwards then . That'll fix up those counterspinning molecules.

Rockman wrote:

duck wrote:It will never run right. You bought a bike that was designed and built in the northern hemisphere. The fuel molecules will always spin in the wrong direction (like your toilets) resulting in suboptimal performance.

I'll ride it backwards then . That'll fix up those counterspinning molecules.

Since you guys ride on the wrong side of the road that might help too.

I'm changing the handlebars on my 75C from the S type to a mid height set meant for a R80, so I got hold of a cable for the K75RT.

This is too long (the inner is 114 cm and the outer 102 cm).

What I need to know is the lengths of the standard K75C throttle cable if anyone has one handy they can measure for me.

I'd estimate I need a cable about 96 cm for the outer and about 105 for the outer.

There's three 87 and later throttle cables for K75s/K100s.

32731457377-969 mm long:   K75S, K100RS
32731457376-1025 mm long: Plain K75 and K75C, Plain K100
32731457378-1142 mm long: K75RT, K100RT, K100LT

Those are not my measurements. They're from the BMW parts catalog.

duck wrote:There's three 87 and later throttle cables for K75s/K100s.

32731457377-969 mm long:   K75S, K100RS
32731457376-1025 mm long: Plain K75 and K75C, Plain K100
32731457378-1142 mm long: K75RT, K100RT, K100LT

Those are not my measurements. They're from the BMW parts catalog.

I'm assuming then that these are the overall lengths for the inner cable. If this is the case then the K75C/K75/K100 (...376) should be what I need. Thanks for the info.

Ready for rego except for new tyres, which are on order. Starts almost instantly, runs well but geez it blows a lot of smoke when it warms up. I half expect the fire brigade to show up looking for a grass fire. Since I've only run it up and down the back lane a couple of times I'm hopeful that the smog will clear after a good run.

Only thing I did notice was wear on the final drive splines so I'll be looking for a good one of those in due course.

Smoky starts:
http://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/smokystart/smokystart.htm

Great news Phil......
Smoke  ... dont worry aboutit till you get a couple of hundred ks on it ...should burn off by then eh ?

Yes I expect it will clear up with a good run. I half suspect most of the oil is in the muffler because it doesnt smoke much at all when first started, its only after everything has heated up that I get smoke. I suppose I could take the muffler off and run it without. If its the muffler then it should be fairly clear - or maybe I'll just go for a ride next weekend

If it helps you feel better, just think of the smoke as mosquito fog and you are doing the neighborhood a service.

Rockman wrote:Yes I expect it will clear up with a good run. I half suspect most of the oil is in the muffler because it doesnt smoke much at all when first started, its only after everything has heated up that I get smoke. I suppose I could take the muffler off and run it without. If its the muffler then it should be fairly clear - or maybe I'll just go for a ride next weekend

Ride it....you will spend more time trying to get the muffler off and back on. It may well be that whoever laid it up put oil in the muffler like we use to do with our old Japanese bikes but they had steel and not stainless steel.

92KK 84WW Olaf wrote:

Ride it....you will spend more time trying to get the muffler off and back on. It may well be that whoever laid it up put oil in the muffler like we use to do with our old Japanese bikes but they had steel and not stainless steel.

K75 headers aren't like K100 headers with separate pipes going into the exhaust can. K75 headers are welded to a collector and much easier than a K100 to attach to the exhaust can. However, they do have a proprietary one use gasket (17) that usually needs to be replaced.

92KK 84WW Olaf wrote:

Rockman wrote:Yes I expect it will clear up with a good run. I half suspect most of the oil is in the muffler because it doesnt smoke much at all when first started, its only after everything has heated up that I get smoke. I suppose I could take the muffler off and run it without. If its the muffler then it should be fairly clear - or maybe I'll just go for a ride next weekend

Ride it....you will spend more time trying to get the muffler off and back on. It may well be that whoever laid it up put oil in the muffler like we use to do with our old Japanese bikes but they had steel and not stainless steel.

I doubt that it was "laid up". Just parked in the back of a shed and forgotten more like.

No I'm not going to touch the exhaust, just ride it and see what happens. It starts easily and runs well so I dont think there is anything wrong, and it has moved the mosquitos out of my shed, which is a good thing.

I finally got to take it for a run on friday after fitting new tyres. There was a big flat spot in the mid range like it was running too rich and bogging down. Maybe the chinese injectors aren't a match for the originals. I did a sort through my collection of injectors (14 in all) and found 3 original Bosch ones that worked. I've yet to take it for another run but "seems" to be better. Smoke haze is clearing.

And a question - I checked the brass screws on the throttle bodies. Two were set at 1 3/4 turns out and one at 1 1/4 turns. What is a good starting point for these? I set all 3 at 1 3/4 turns but haven't balanced them yet.

I usually put #1 at 1 1/4 to 1 1/2 turns out and then balance the other two to that. Doesn't hurt to take the brass screws all of the way out first to ensure that their tips are clean before balancing.

duck wrote:I usually put #1 at 1 1/4 to 1 1/2 turns out and then balance the other two to that. Doesn't hurt to take the brass screws all of the way out first to ensure that their tips are clean before balancing.

Thanks Duck. I'll clean them then set all at 1 1/2 and balance them from there. All after a good run to settle the "new" injectors and everything else in.

Hi Phil,  in addition to cleaning the needles ...  soak a pipe cleaner in carbi clean and push it through the jet into the throttle body  to clean off all the carbon that settles there , there is a lot of spitback that settles in that port

Just a heads up

If the flat spot persists , i could service the afm for you .
Cheers

charlie99 wrote:Hi Phil,  in addition to cleaning the needles ...  soak a pipe cleaner in carbi clean and push it through the jet into the throttle body  to clean off all the carbon that settles there , there is a lot of spitback that settles in that port

Just a heads up

If the flat spot persists , i could service the afm for you .
Cheers

Hi Charlie. A change of injectors back to OEM fixed the flat spot problem. I took it for a run yesterday and it ran clean at all speeds including a couple of bursts to 140 passing traffic so I'm happy with it as is. The headlight fairing is loose and the blinker unit is misbehaving but apart from that all is well. Smoke has gone too.

I did take the needles out. They were actually quite clean so I just gave them a wipe with a green scourer and put them back in set at 1 1/2 turns out. I'll do a proper balance one day.

great to hear 

ride well mate