'86 K75S mission to accomplish better fuel consumption

[Laitch]

Are the wheel bolts tight? :giggles

It might bearing failure at the crown gear. Review this thread.

[daveson]

Maybe grab the wheel, check bearings for in out, up down, left right, forward back.

[szabgab]

Are the wheel bolts tight? :giggles

It might bearing failure at the crown gear. Review this thread.

Thanks Laitch,  wheel bolts are tightened to the specified torque values,  as I bought a new toy and done up everything to spec :)  I have checked again today,  and it is not loose.  Every time I do something to the rear of the bike (pun not intended) I do check for wobble,  but there is none,  and if I turn the wheel by hand, everything seems to be nice and smooth....

[szabgab]

Maybe grab the wheel, check bearings for in out, up down, left right, forward back.

I did that straight after doing the video... Wheel is nice and secure and there is no play in any direction. However one thing might correlate to our previous discussion, 3.20 is stamped on the FD housing, but RPM in 5th suggests other ratio... Could it be, the innards were swapped at some point and the spacers are not the correct thickness? I guess it is very hard to answer such a question though :)

[daveson]

Is the disc on tight, and centralised, or I spose it is warped.

Although adding confusion, the riders manual suggests 4,000 rpm at 100 km/h, but my k75 is like yours and at 4000 rpm does about 92 km/h.
From memory, your instrument cluster is not original, not sure if that is the reason.

So not as much of a drama as I thought, unless mine is out of whack also. Another thing wrong with mine, which i didn't notice except for a previous thread of yours, the fuel return spills onto the burrito. Good one, thanks for that, i think. :)

[Laitch]

Is this normal (even though I am sure, rattle of any kind is not healthy)? Could this be something, that is causing fuel consumption issues? What is this thing and did anybody come across something like this? Is it serviceable?

The rear wheel shouldn't be making noise as the wheel is rotated. If the replacement disc is wobbling similarly to its predecessor then the two discs need to be compared by a machinist side by side for thickness variation and runout. If the discs measure within spec and there is nothing defective about the surface onto which they are mounted, the caliper assembly might be faulty or a bearing in the final drive might be at fault.

Remove the brake pads and spin the wheel to determine if a noised develops. The engine sound masks the noise right now. Whether the condition is serviceable depends upon what is causing it. Determining that is likely to take disassembly.

[Laitch]

Another thing wrong with mine, which i didn't notice except for a previous thread of yours, the fuel return spills onto the burrito.

There is nothing wrong with that. In later models, the return line ends above the "burrito".

[daveson]

Hi Laitch,  right you are.

It's just that after pulling my triple out of storage, and with Gabe's previous thread in the back of my mind,  I looked and noticed it's the same. I thought,  that'd be right,  another problem I didn't know I had. luckily, in my case,  it's not noisy.

I spose it's like a mini reserve tank,  dumping fuel on the opposite side of the pump. On one of my first rides of my brick,  when the fuel gauge wasn't working, I couldn't get fuel in the second last town I went through. About five Kay's before the last one it was stumbling, I leaned the bike to the left,  and just skimped in.

[szabgab]

The rear wheel shouldn't be making noise as the wheel is rotated. If the replacement disc is wobbling similarly to its predecessor then the two discs need to be compared by a machinist side by side for thickness variation and runout. If the discs measure within spec and there is nothing defective about the surface onto which they are mounted, the caliper assembly might be faulty or a bearing in the final drive might be at fault.

Remove the brake pads and spin the wheel to determine if a noised develops. The engine sound masks the noise right now. Whether the condition is serviceable depends upon what is causing it. Determining that is likely to take disassembly.

OK, I will have to investigate the wobble of the disc, I guess for initial assessment a flat sheet of glass will do... Although the noise is coming from the FD and the rear wheel shakes and turns unevenly at every rattling noise I can not replicate that with only the wheel turning it has to be in gear and at slow wheel speed it to be noticeable. If I spin up the wheel in 5th whilst on centre stand and kill the engine with the clutch pulled, the wheel stops quickly, as the rear rotor wobble against the pads causes it to stop, but that strange rattle and unevenness is not manifesting itself. Funnily enough if I turn the wheel by hand the wheel rotates a lot easier and that underlines my earlier suspicion, that the drag at the rear wheel is more present at speed, or maybe only more noticeable.... I might be able to source a K100 FD, however I would have to disassemble it, as it is a 16T version and I have read at your link, the crown gear would have had to be re-shimmed which is way beyond my capabilities I guess. My pinion seal is slightly leaking too but the removal and replacement of a new seal is rather involved with a 36mm socket, special holding tool, fabricated castle nut wrench, silly torque values etc so I guess first I would have to check the crown gear bearing for notchiness. I just really hope, this is not some gear box trouble that is manifesting itself at the wheel (however with the wobble in the rear disc there is something strange, maybe the bike was dropped at speed or something, and the whole wheel assembly got a hit)

[daveson]

Maybe a FD and a drive shaft.  I think you said you shaft was worn anyway.

[szabgab]

Maybe a FD and a drive shaft.  I think you said you shaft was worn anyway.

No, driveshaft is fine-ish, the previous one was worn beyond acceptable level, so I bought a 'new' one from this forum (albeit u joint is notchy, so that might be of some concern)

[Laitch]

albeit u joint is notchy . . .

:grimreaper:

[daveson]

What is the FD ratio of this FD you can get? How many teeth on your drive shaft now?  It's probably also 16. You might be able to kill two birds with one stone here,  it will probably improve your fuel economy, although going too far sometimes has the opposite effect.

[szabgab]

:grimreaper:

Uh, that sounds reassuring :S

[szabgab]

What is the FD ratio of this FD you can get? How many teeth on your drive shaft now?  It's probably also 16. You might be able to kill two birds with one stone here,  it will probably improve your fuel economy, although going too far sometimes has the opposite effect.

I am not sure, the guy selling it will look up the ratio over the weekend, just as the teeth count. Mine is standard K75, so 20 teeth. On my old Honda I went into great length to replace a perfectly good chainset to a closer ratio, it did nothing to my fuel consumption...

[daveson]

Hi Gabe,

Just read on Soggz' mega thread you like your idle at 1200, and that at 850 the battery light glows. The riders book says set it to 950, that should improve your fuel economy.

Anyway, how's the final drive drama going.

[The Mighty Gryphon]

Hi Gabe,

Just read on Soggz' mega thread you like your idle at 1200, and that at 850 the battery light glows. The riders book says set it to 950, that should improve your fuel economy.

Beat me to it.

[szabgab]

Hi Gabe,

Just read on Soggz' mega thread you like your idle at 1200, and that at 850 the battery light glows. The riders book says set it to 950, that should improve your fuel economy.

Anyway, how's the final drive drama going.

Dave, Gryph, thanks, and sorry for the hiatus, I have been off the grid for a while :) I have thought the same thing, when I wrote the RPM thing on Soggz' thread, that surely that is a problem, but unless it highlights a problem (which I am sure it does), I spend probably 1/1000th of my time riding at idle, so that alone would probably not cause fuel economy issues. Also there is an another thing, that bugs me since the good weather is upon us, namely the need for a choke... If I leave the bike for more than 15-20 minutes, even in this very nice +20-25C weather, I need to engage the choke on half a setting for a bit, otherwise the bike wants to stall on me. I am sure, these things are somewhat connected (and pointing towards some mixture ailment, even if my plugs are nice and tan)...

[daveson]

Hi Gabe,

Masking an idle problem by increasing the revs,  is a good way to forget you have a problem. I don't remember, did you do Martin's air/fuel ratio test, warm,  1000rpm,  press starter?

I was surprised when I did the maths on what was my typical ride (regarding idle/total ride time ratio)  Half hour start to stop,  two minute warm up, four, one minute traffic stops. I would have guessed that at one percent, but it's twenty. 

[szabgab]

Hi Gabe,

Masking an idle problem by increasing the revs,  is a good way to forget you have a problem. I don't remember, did you do Martin's air/fuel ratio test, warm,  1000rpm,  press starter?

I was surprised when I did the maths on what was my typical ride (regarding idle/total ride time ratio)  Half hour start to stop,  two minute warm up, four, one minute traffic stops. I would have guessed that at one percent, but it's twenty.

Hi Dave,

Yeah, I know.... Sticking my head in sand won't make the problems go away :D

So just to recap, where we are now - idle is high - 1100-1200RPM, and I can not get it any lower, I have tried today, I am at the end of the adjustment. Whenever I am lower, the engine is cold and maybe that makes it stuttery

Bike needs choke, whenever colder than piping hot - e.g. driving for 15 miles in 20C I can restart it immediately without the need of choke. If left for 15-20 minutes, some choke is needed, otherwise bike stumbles or it is hardish to start

Rear disc is getting hot even without using the rear brake. In comparison the dual discs up front will not get as hot even though they have been used properly. By hot I mean hot as to be able to hold the rotor, so I'd guess 50-60C. The wobbly disc, I have showed in the videos were replaced by a straight one bought of a member of a local BMW club, no change, even though the rear wheel rotates a lot more freely. FD, DS I did not touch as of yet, so they are the same old ones.

I have not checked the plugs after a short ride as Gryph suggested, will do that next, as they are the same perfect colour after a day's ride.

The Martin / Lentini method does nothing to my idle, pressing the starter button, whilst bike is running makes no difference.

I checked again today, I have NO detectable air leaks anywhere. Spark plugs - correct range, correct gap, valve clearances correct, TB's synced, TPS set. People driving the same type of a bike in similar circumstances report some 20-30% lower consumption.

Maybe I need to

a) stop obsessing and drive the bloody thing (driving it is not a problem, not obsessing, well that's another story)

b) take the bike for a proper CO, fuel pressure, etc analysis and stop obsessing.

c) do nothing to the bike but visit a psychologist, who could help with my OCD :)

[The Mighty Gryphon]

How far are the idle air screws on the throttle bodies backed out?   

I stumbled across a reference not long ago in a BMW tech bulletin that said they should be between 3/4 and 1 full turn out from lightly bottomed.   I ask because, first of all, you have what sounds like too much air at idle.   Also, my four valve K100RS had a high idle of about 1050 rpm, and I found the idle air screws were out between 1 3/4 and just over 2 full turns.  Bringing them in to about 3/4 turn brought the idle down to around 900 rpm.

I don't know if the idle air setting or idle speed affects the fuel injection, but it wouldn't hurt to get it down to the 900-1000 rpm range.

[szabgab]

How far are the idle air screws on the throttle bodies backed out?   

I stumbled across a reference not long ago in a BMW tech bulletin that said they should be between 3/4 and 1 full turn out from lightly bottomed.   I ask because, first of all, you have what sounds like too much air at idle.   Also, my four valve K100RS had a high idle of about 1050 rpm, and I found the idle air screws were out between 1 3/4 and just over 2 full turns.  Bringing them in to about 3/4 turn brought the idle down to around 900 rpm.

I don't know if the idle air setting or idle speed affects the fuel injection, but it wouldn't hurt to get it down to the 900-1000 rpm range.

Gryph, I have done, what was described in the TB balancing thread, backed them out 1 1/5 turns as an initial setting, but that resulted in too high idle even in the lowest setting of the idle speed screw, something like 1500RPM. So I adjusted the first TB lower, which dropped the idle speed and set the other two accordingly, so it is all in balance. I might just set the first screw even lower, however I did not want to do that before, as I would have to more or less close the bypass. I think, the butterflies are out of sync, as the first one (closest to the front of the bike) needs 3/4 to 1 turn of a different setting, as the other two, but I am not touching the blue screws :) Also my TPS is bottoming out, so I will have to get it balanced, whilst juggling multiple things at the same time but I will try my best :))

[szabgab]

OK, so I keep coming back on this. Final drive I have left alone for now, as the guy selling it locally thinks it is worth approximately 3-4 times as much, what they are sold on the bay (looking at the dream-on buy it now prices does not help :) ) However I had to dig in my tank yet again, as the cicadas dampening solution became dislodged from the return pipe. During this I have removed the fuel filter, even though I have replaced it not 1000 miles ago. It is hard to blow through it, even if I let it dry for +/- 1 hour, but bike runs the same with or without. There is a discussion over at K100 how a partially blocked filter can affect the cold start / idle routine, but I would have thought a fuel pressure problem manifests itself more on the high revs, also there is PLENTY of fuel streaming back. Unfortunately I have thrown away the old filter, so I can not check, what resistance that has after a few months of drying. What is your experience on the blow through test? Thanks!

[daveson]

I would think so too.

Installing a new one would show if there is a difference, but unlikely, I think.

Idle speed adjustment screw o rings? Suggestions not tried yet?

[szabgab]

I would think so too.

Installing a new one would show if there is a difference, but unlikely, I think.

Idle speed adjustment screw o rings? Suggestions not tried yet?

The o-rings are fine Dave, as are the other rubber bits, I have liberally sprayed the whole area multiple times with starting fluid to check for leaks with no change in idle speed. I have even taken the MAF off again, sprayed the temp sensor with contact spray, taken the top off and sprayed the carbon track with contact spray - no change. Everything works as it should but something is amiss...