pajonk wrote:i wanted to ask you guys about how to check the impendances in the air-flow meter

Here you got it.

Inge K.

vielen dank!

Ordered a used AFM off of E-bay today. I will update once I get it installed.

thanks
Brad

pajonk wrote:vielen dank!

Bitte schön!

Brad one of the things not mentioned as yet is the normal ability of the K100 to backfire when the throtle is opened above 2000rpm on de-accelleration, due to the fi unit shutting off fuel till required by the ride with a throttle opening such as a blip before a down shift. So your concerns here may be missing that relevant detail. Aside from the possible airleak at the header to head gaskets,or header to muffler. Also you have not mentioned that you cleaned the right hand switch block with the starter and kill switch on it. They will contribute to poor electrical performance if not attended to. A response to the carb spray on the throttle bodies would help us thinkers on the side try to help resolve this issue. I would spend time on the electrical connections of the coils. In the beginning you mentioned the noise from the fan when it cut in, I have read of a tell tale sign, of inerference from the fan on the ignition signal in another post on another site. My shed pc may have it I will have to check tonight. regards keith

Thanks Keith,

Im having some backfires even with throttle closed, but typically with hard downshifts.

I'll double check with the carb cleaner at throttle bodies tomorrow, but in my last tentative attempt, it didn't seem to make any difference in the idle.

You make a good point about the starter switch. I will do that tomorrow as well

Best
Brad

OK, so the used AFM came in yesterday and I popped it in last night. First thing I noticed when I had both out was that the bypass screw on my original was screwed almost all the way down in comparison to the replacement which was probably near the top of the threads. Replaced the AFM and also popped in a new air filter just so I know it's good.

Things seem quite a bit better. Still hearing some strange sounds upon startup idle, but the throttle response is as good as it's been and the surging seems to be gone. I'm not sure if the fix was a different AFM or a different setting of the bypass or maybe a combo, but things seem to be significantly better. I think I'll ride her for a week and then see if I feel like delving any deeper to get her purring perfectly

thanks for the help all...
Brad

Since bike seems to be running better.... I sprung for some new rubber. Currently rear is 5 yrs old with good tread, front is 12 YRS OLD!! with good tread but that has got to be getting crumbly...

Anyhoo, have a set of Bridgestone Battlax BT-45s Sports on the way. Hopefully have em on by next week for a bit longer ride

B

sweet news brad ....



hay mate! now your up to that stage i would suggest a tune up by someone with a gas analizer and a good timing light ....



congrats ....



good idea for the rubber too ....enjoy

So, of course I decided to delve deeper. Was still feeling something not right. One day on the ride to work it felt kind of like it was running on only 3 cylinders... Power not quite what I expected unless I really wrung out the throttle and a slighty rough feel and sound from the engine. The night before I had tweaked the position of the TPS for less slop. I surmised that I had probably bumped the ignition wires connections at the coil and began to suspect bad wires. I had tested the resistance of the wires before and they seemed to look ok but intermittent cables can be deceptive. Ordered up a replacement set from euro-moto electrics. Yet to arrive.

Also was suspect that the throttle bodies needed resynced after all the interim activities so got a SyncPro this weekend and hooked her up. After calibrating it, I hooked up all 4 lines to the bike to find #1 significantly lower than 2,3 and 4. Check out a quick youtube video of a test below. Couldn't get things even close with the brass screws so I left things be for a bit.

After a bit of a think decided to check my valve clearances. I already know compression is good but hadn't checked the valves since purchasing. This was a first time project for me, so it was quite fun to get in there and get a bit of oil on my hands. After sacrificing a roll of paper towels and a spot free driveway, I came away to find my clearances seem to be looking pretty good. So I button her back up.

Then decided to poke around on those ignition wires a bit and see if I could find a weak spot. In the process of doing this I pull the wires off the bottom of the coils and peer up into them... hmmm, #1 looks different... Pull off the coils and find that the high voltage terminals on 2,3 and 4 are bright and shiny and #1 looks super dull and kind of dark ( see pic below). Ok, so I treat the terminal with DeOxit twice and and am able to clean off something but the terminal still looks very different. When I go to measure the resistance I am perplexed. I get the expected couple of ohms on the spade terminals but between the two hi voltage terminals... It reads as an open. In fact both coils are like this. I know that some K75 had gaps in the coils but did K100s?

Put the coils back on the bike she starts right up but still has the same vacuum issue on 1.

So, not quite sure where to go next...

-Look for vacuum leak? Intake boots are new but it could be the air box to throttle body rubber. Tried to do the carb cleaner test a while back and couldn't tell a difference on any of them. Maybe I'll try that again and focus on 1.

-ignition? New wires should be here soon. How would/could ignition issues affect vacuum? New wires are on the way, not sure what to think about the testing I did on the coils.

-is there some Bavarian war dance I need to perform before I ride every day?

Thanks all
Brad

Throttle sync video

purk ....you have found one of your problems ......i have found that the high voltage terminals discolour quite significantly ...if there is an open circuit in the coil...

the measurements i have found are 10 k round abouts between the high voltage outputs ....a question ? did you move the meter to an appropriate range ....if you were on a low ohms range ...it might look like they are open circuit ...you would need to have the meter set to 100.000 or anything more than 20,000 ohms for this test .....or something like it ...if its an auto range meter ...no worries .

i would be looking for a new coil to replace the one with the blackened terminal at least ...and remeasuring again in any case ...deoxit on the primarys terminals (should measure 1.8- 2.4 ohms from memory ) dont forget the earth (quite important )

i think what happens is the coil develops a hot spot around the high voltage terminals internal to the insulated casing ....the wire from the coil is welded to the terminal at that point (and i think becomes a weakened state over the years. i would imagine that running with high resistance cables would amplify the voltages till they build up enough to "jump over " the gap ...every time this happens the gap progressivly increases as the copper turns to carbon ...you may still have an effective spark developing but my theory is that it will be weaker than a good one anyhow ...

look on ebay for replacements ....then ask the seller to mesure the secondarys ...before bidding ....ask me how i know ..

re the vacume difference ....check your butterfly journals (the bit that holds butterfly on the shaft that goes through the throttle body )and see if they have movement around the bushes that hold them in place .....

other than that they linkages might just need tweeking ....but its a sensative job and not for the faint hearted to get it right ....there are threads in most places about the adjustment .



hope this helps

The chicken bone dance helps. But you have to turn three times round for a K75 and, of course, four for the vier zylinder K100. These techniques are never scientific and a fair bit of art is required, but if you get the rhythm right then Bob's yer uncle.

Thanks Charlie99. I have a few multimeters, all auto ranging. Tried measuring on 2 different flukes and even set one to manual but I get infinite resistance on both coils on both meters. Curious thing is that I found a good looking pair on eBay, asked the seller to test and he came back with the same results. Ordered them anyway as he had a money back guarantee.

Regarding the vacuum issue. I checked the throttle bodies at the spots you suggested and something does look a bit different. Attached is a pic and my observations. It does look like these inter throttle body screws have been monkeyed with before. Thoughts?

Thanks!
Brad

In a word, NO! Unless you have the required tools and knowledge. You can only adjust the TB syncro via the airscrews for idle and just off idle. See the many posts here about this. You need to be able to measure the large volume of air passing through with accuracy. It is not the same as a bank of carbies on a Japanese litre bike from the '80s.

certainly looks that way to me ....but im no expert at the dark arts of finessing vacumes

i guess what you are trying to do is adjust the number 1 closed a little more (more vacume) the real test is when you open up the throttles to a steady rev a fair bit higher than idle ...and compare them then ..but as i said its a thing i would be playing with without backup from a workshop that could reset them properlly .

gee they look clean though ....nice

a point worth making ...our old friend og ,,,had replaced his rubbers and had to remount them as his first attempt didnt work just right .....food for thought ...as leaks in the rubbers could also be giving a funny reading



btw ...is that another take off tube attached to the tb .....or just a piece of hose at number 1 ? dont think ive seen that before .

hmmm did you clean out the jets in each tb .....those adjusting screws hide a needle and seat (jet)at the bottom of the thread ....i noticed when twb had his apart that an awfull lot of crud had accumulated in there ....

if your buying open circuit coils your just delaying the thing breaking down....they will go west.... in time

just a thought

Well, despite warnings from tinkerers far more experienced and wise that myself (thanks nonetheless, TWB), I decided to have a go at adjusting the linkage or #1. There are stop nots on there which seem to be welded (maybe JB weld or something) in place, so there is no tightening those screws without replacing them. Luckily that wasn't the way I needed to go... I needed to loosen the screw which would in turn further close the butterfly. Did so with the SyncPro hooked up and saw immediate and dramatic reaction on the gauge. Loosening the screw (closing the butterfly) increased vacuum. Matched up the cylinders and then tried increasing throttle to about 3k RPM. Cylinders were fairly mismatched up there so I tweaked for a bit and was able to adjust it so that the brass screws are within a turn or two of each other at most and all cylinders are pretty well matched at both idle and 2500-3000 RPM. They are still a bit off at the higher RPMS, but "close enough for rock and roll" as we say at work.

Test ride and.... the bike is considerably smoother. Woohoo! Still something lingering, but I am hoping that the coils that are on the way should help to solve that. May still be getting a bit of a weak spark in 1 due to that bad coil. Hopefully those will arrive this week and I'll know for sure.

In the long run this all only took me about 35 minutes (including the test drive) so, I am pretty happy with the results. Now, with that said, I can imagine that trying to adjust the linkages for all the throttle bodes would be a pain in the booty, so I'm not sure I'd suggest other people go there right away, but in my case it seemed like a risk worth taking.

BTW - Charlie99, that other hose is a connection to the vacuum switch that was removed in mid 85.

No, I didn't clean the jets Charlie. Maybe next weekend

ah ! that explains it then ,,,thanks ..i think if it was not being used plug it like the others ?

My K is early 85 so it has the vacuum switch. It's mounted on the back of the throttle bodies. Just reading up a bit more now and it sounds like it was supposed to advance timing once steady vacuum was attained at speed. In a thread elsewhere I read that BMW deleted it since it never quite worked right and caused surging at speed. Hey, sounds familiar. Sounds like I should remove this switch and cap the vac port.

You can if you want. just another potential source of a vacuum leak.

If you have decided to tinker with the throttle body connecting screws (against all advise) as you think the previous owner couldn't leave well alone as well a few tips:

Original setting is being done by BMW over a special rig that measures air flow. There is no way that we can try to achieve that level of synchronisation with our 'hobby' tools. Having said that, there are ways to get pretty close.



One is to take the bodies off the bike and, taking the body where the gas cable operates directly on as a base setting (!!) and having it slightly opened (3mm drill bit/feelers at .3 mm??), verify that the others open to the same extend - if not adjust.

On the bike - (after having verified that the valve clearances are OK, bypass screws clean with good O-rings, etc) close the bypass screws. Open the gas a bit by putting a ring or else underneath the part where the throttle cable attaches and start the bike. Hopefully your filler part is of such a thickness that the bike idles at about 1500 rpm. Then use the vacuum stuff to compare. You are now comparing the throttle plates with each other. If you can't withstand the urge (or there is a serious mismatch) adjust the throttle plate screws to achieve calibration. You can try to see if it is the same at 1500 and 2000/3000 rpm (if not airleak or valve clearances??). If Ok you stop the engine, remove the filler and open up all the bypass screws about 1-1.5 turns. Start the bike again and check synchronisation as normal. Some bikes need to have their idle adjusted with the screws, others with the set-screw. Idle is 950 (+/- 50).

Off course the above only works if you don't have any air leaks!

Minor update....

I rode her in to work this morning (15 mile commute mostly on the freeway) and she is running as smooth and strong as she ever has. Darn near a new bike. I'm really glad I took the plunge and tried adjusting that linkage screw. I'll likely leave it as is for now, but will plan to take the throttle bodies off at some point in the future so I can get a look at how the butterflies actually sit at idle.

New plugs wires and coils should be here this week and I'm excited to see what difference those might make. This bike is getting more and more fun to ride!!!

Brad

Good on you for trying and improving, as I have said elsewhere the problem is those screws look waaaay too inviting to previous owners who cannot resist a twiddle so if the lacquer is already broken it is clear they are likely to be out of adjustment and doing the adjustment with the correct tools as you did is almost certain to bring about an improvement. If the locking lacquer is unbroken then as TWB say leave them alone.
Regards,
K-BIKE

Thanks K-bike, I'm pretty proud of the results especially considering my shade tree pedigree.

I received the new plug wires and replacement coils (used) yesterday and installed them last night. Test ride today and things are even smoother and more responsive. I think she finally starting to feel like a real k bike. Seems I had multiple issues which were all combining to cause my poor performance. Thanks to all for the good advice and encouragement to get me where I am today.... a happy rider!

Brad

Well done Brad what an excellent result! Good on you for diagnosing the issues one by one.
Regards,
K-BIKE

Great stuff mate, another one back on the road running good!

nice result brad ...good riding to ya !!!!

Great result Brad!