CO screw adjustment question.

[Qwodracer]

So i bought my k75 with problems.. I think the previous owner was messing with things trying to make them work... I have tested everything electrical many many times. Ignition shows no faults on oscilloscope, cleaned all connections and grounds, have a fuel psi guage, and it stays steady 35+ even when running rough. Replaced fuel injectors, Coolant temp sensor, and many many sets of plugs. They just foul out, ive gone 200 miles on 5 sets of plugs.. Bosch x5dc and NGK bp7ea.


There is a screw that changes how much air bypasses the vane in the air sensor. So today i was running out of ideas because EVERYTHING always tests good, (air temp, vane voltage, coolant temp, tps, hes, signal at the coils..) i decided to pop the rubber grommet and see how far out the screw was.. it was about 1.75 turns out from bottomed out. So i went for a ride and just kept turning it, it seemed to be making the bike run better and better. Mind im still on fouled plug, but i got to 13 full turns out before i ran out of time to keep playing.. so if its 1mm pitch thread then thats 13 mm i have open for air to bypass the vane door. Idk... just seems odd to me, so i figured id ask.


I dont have a sniffer to properly test/adjust it, Sunday i will get some time to play a little more, and i have another set of non fouled NGK to throw in, really hoping this is my issue. Just that going from a carb where 1.5-2.5 turns is the recommended adjustment are, 13 turns seems excessive, i will do more if i must, but perhaps ive already gone too far, and should look for other reasons it is too rich?

[Qwodracer]

Also drained fuel and replaced filter and fresh fuel.

[Martin]

Look up lean drop method for adjusting mixture. The early 75's and 100's 2v models had a neat little hardly known feature. With the bike idling at 1000 Rpm push the green starter button ( this will not do any harm) if the mixture is right the revs should stay the same or rise slightly. If the revs rise a lot or drop you need to adjust the mixture.
Regards Martin.

[Qwodracer]

Look up lean drop method for adjusting mixture. The early 75's and 100's 2v models had a neat little hardly known feature. With the bike idling at 1000 Rpm push the green starter button ( this will not do any harm) if the mixture is right the revs should stay the same or rise slightly. If the revs rise a lot or drop you need to adjust the mixture.
Regards Martin.

Lol, well I have been doing this, not knowing it's an approved method 😎 I did know, It bypasses the temp sensor inputs and supplies a full 12v to the injectors,


So I'm just looking for verification that 13 turns out is normal?

[Martin]

What happens when you push the start button when the idle is set at 1000 Rpm.
Regards Martin.

[Laitch]

So I'm just looking for verification that 13 turns out is normal?

http://www.motobrick.com/index.php/topic,5202.msg43520.html#msg43520

[Qwodracer]

Thanks for the link. I foollowed the steps there and have it currently set at 8 turns, and just increasing 50-100 rpm


However bike is still running like poop.


Timing is at 0
Co adjustment set.
New injectors (previous ones were plugged)
New fuel filter
New plugs at .028gap
New coolant temp sensor
Watched the HES on an oscilloscope hot and cold.. no drops.
Cleaned motronic connector
Cleaned grounds.


Idles great, revs in neutral just fine, but release the clutch and there is no power.

[wally.fisher]

Thanks for the link. I foollowed the steps there and have it currently set at 8 turns, and just increasing 50-100 rpm


However bike is still running like poop.


Timing is at 0
Co adjustment set.
New injectors (previous ones were plugged)
New fuel filter
New plugs at .028gap
New coolant temp sensor
Watched the HES on an oscilloscope hot and cold.. no drops.
Cleaned motronic connector
Cleaned grounds.


Idles great, revs in neutral just fine, but release the clutch and there is no power.

Timing set at 0 ???, is that right?


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[Martin]

Unless you modify the plate, the timing is fixed on the Brick. There are posts on how to do this.
Regards Martin.

[wally.fisher]

Thanks for the link. I foollowed the steps there and have it currently set at 8 turns, and just increasing 50-100 rpm


However bike is still running like poop.


Timing is at 0
Co adjustment set.
New injectors (previous ones were plugged)
New fuel filter
New plugs at .028gap
New coolant temp sensor
Watched the HES on an oscilloscope hot and cold.. no drops.
Cleaned motronic connector
Cleaned grounds.


Idles great, revs in neutral just fine, but release the clutch and there is no power.

Head over to the K100 forum, or google timing for the k timing setting which I believe should be 6 deg btdc.


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[Martin]

How to modify the timing on your Brick.  http://skylands.ibmwr.org/tom/tech/k75_timing.html
Regards Martin.

[Qwodracer]

Unless you modify the plate, the timing is fixed on the Brick. There are posts on how to do this.
Regards Martin.

I don't know, didn't look modified... as I turned the plate the timing changed.


I will try setting it back at 6, that's where it was originally, so I do t think that will change anything.


I will also add I did a ful voltage sweep on the vane and owned out all the sensors, everything appears fine...  I have been able to go 250 miles on like 3 almost 4 tanks now so it's definitely fresh gas and 2 fresh filters.

[Qwodracer]

Just wanted to update everyone. 3 years later… the bike was sitting, I replaced the pvc vent elbow hose, starter brushes and new injectors, and found water in the tank after sitting outside 2 years, the fuel pump ended up seized due to rust, so that’s all new and the bike runs again :) it’s possible the pump was on the way out or the starter was shorting out 🤷‍♂️ Not sure which it was but the bike is running good, have the CO screw about 6.5 turns out right now and the bike runs great.

[Laitch]

Just wanted to update everyone. 3 years later…

Thanks for the update. Did you balance the throttle bodies before the CO adjustment? How many miles have you logged since you made it run well? It must be a good feeling to finally get on the road with your Brick. 

[Qwodracer]

Thanks for the update. Did you balance the throttle bodies before the CO adjustment? How many miles have you logged since you made it run well? It must be a good feeling to finally get on the road with your Brick. 

I really need to get some carb sticks so I can. I did not, but I never messed with them so I would think they are still set from the last time the bike ran well. So I haven’t logged any miles really just running up and down the road to the gas station while tweaking the CO screw to the butt dyno.

The bike fell over in a snow storm, and broke the two right side turn signals, so I haven’t fixed them yet, it also needs some love from sitting outside for 2 years. It’s also not currently registered, inspected, or insured. I sold my project car a month ago and ordered everything I needed to fix this bike up this far. So planing on getting the legals done and then I can ride free :)

[The Mighty Gryphon]

No need for a fancy balancer, a lot of us get by quite nicely with a couple bottles, corks and some tubing.  I built my balancer for under $20 and got to drink two bottles of Snapple. 


Throttle Body Balancer 003.JPG (55.15 kB . 768x576 - viewed 1922 times)

You set the idle air on the last cylinder(the one that connects to the fuel pressure regulator) to about 1 1/2 turns out and then adjust the others to equal the vacuum on that one.

The principle of balance is that you are trying to adjust the idle screw on the throttle body you are matching to the last one so that there is no fluid going from one bottle to the other.  When the level in the bottles stops changing the vacuum in the second throttle body is exactly the same as in the reference one.

[Qwodracer]

New update:

Bike is now registered insured and passed state inspection. Getting ridden frequently. It does run rich still. Stalls after long idles and does load up under some load conditions on the road and bigs down.

I also picked up a vacuum gauge balancer so I was able to balance the throttle bodies at 4-5inches, but, the center throttle body is completely screwed tight and the other 2 tb adjustments are about 2 turns out

From what I read here I want to be about a turn and half out to start, and on my gauge that’s like 6-7 inches? Does this mean I have a Vaccuum leak or possibly bad intake valve?

[Laitch]

For a throttle body balance to be effective a few tasks need to preceded it.
The air filter needs to be clean—not new—just clean.
The valve clearances need to be checked, and adjusted if necessary.
The fuel filter needs to be in good condition.
The spark plugs need to be in good condition.
The manifolds to the throttle bodies need to be checked for leakage using propane or, if carefully applied, volatile carb cleaner and replaced if necessary.
The z-tube needs to be in good condition. You've checked that.

After all that is completed then balance the throttle bodies. The scale reading doesn't matter; they just need to align at the same level.
After the balance, set the CO level.

You've been random in your tasks. This order might help.

[Qwodracer]

For a throttle body balance to be effective a few tasks need to preceded it.
The air filter needs to be clean—not new—just clean.
The valve clearances need to be checked, and adjusted if necessary.
The fuel filter needs to be in good condition.
The spark plugs need to be in good condition.
The manifolds to the throttle bodies need to be checked for leakage using propane or, if carefully applied, volatile carb cleaner and replaced if necessary.
The z-tube needs to be in good condition. You've checked that.

After all that is completed then balance the throttle bodies. The scale reading doesn't matter; they just need to align at the same level.
After the balance, set the CO level.

You've been random in your tasks. This order might help.

All that is new and installed by me. He spark plugs have been fouling out and I’m 3 days old on the newest set. Valves were checked when I had given up on it and was within spec,  I do not remember what they were. I even just used a kn cleaning kit on the kn air filter. Carb cleaner on the boots and throttle body does not affect the idle. Not sure how to do propane testing…

So is it not a problem that the center throttle body adjustment is bottomed out?
They are balanced now.. it does idle smooth and pushing the start button does change the idle slightly

But it still loads up and backfires when decel

[Laitch]

It's a problem. Review what you have done.

[Qwodracer]

Considering it was an issue with the bike when I bought it, and I have yet to correct it, and have only rode the bike 300 miles in 4 years, I highly doubt it’s anything I did, or looked at yet.

Technically I’ve done nothing to the throttle bodies. Having the bypass screw adjusted fully tight means air is getting in and not needing the bypass. Also if I loosen the screw, the vacuum doesn’t change, I’ve gone 5 turns out and it still doesn’t rise, Could something be holding the throttle plate open inside the bore ?

How do you take the clamps off the throttle bodies? They appear to have a special crimp on them. Is there a tool to take them off and put them back on?


Things I did in 2017: (first 200 miles)
New tires
Greased the spline
New fuel filter
New Maf
New oe coolant temp sensor
New Hal sensor
2 oil changes (there were saturated with gas)
Compression test (about 150-160 psi with cylinder walls washed down by excessive fuel)
Measureed valve tappit clearance
Removed and cleaned all grounds also added more grounding straps
Cleaned starter
New spark wires
Several sets of spark plugs in this time.
Deoxit on every connector.
Installed fuel pressure gauge. Runs at ~35psi all the time

The bike sat for 3 years 2 of which were outside in covered in snow and rain.

Then everything I’ve done since may 2021 mostly before driving the last 100miles

Flushed brake fluids and cleaned the masters
New crankcase elbow
New fuel pump (water was in tank from sitting outside and rusted the pump)
New fuel filter
New fuel injectors
Cleaned the tank
New gas + heet
Rebuilt starter with new brushes
Cleaned and oiled air filter
Replaced turn signals
Fixed hazard switch
Registered insured and state inspected.

And then yesterday I double checked for vacuum leaks using carb cleaner and used my new vacuum gauges to “balance” the throttle bodies. Set idle, and tried to find the sweet spot in the co screw. But still hesitating 2-4K and loading up at stop lights which is exactly the problem it has when I bought it and was trying to fix all along.

Things I have yet to do: leaky valve cover, leaky crank cover and the orings on the bolts on both. both will leave the occasional 2 inch oil puddle.

[Laitch]

Considering it was an issue with the bike when I bought it, and I have yet to correct it, and have only rode the bike 300 miles in 4 years, I highly doubt it’s anything I did, or looked at yet. 

You're not the first to think that. 

Riding the moto only 75 miles per year also contributes to the problem. Have you followed the steps in the troubleshooting guide in the Repair Guidance section, or is that also something you've already done but not indicated yet?

Use cutters to remove the oetiker clamps on the throttle bodies. They are one-use-only clamps. They're out there for sale or can be replaced with screw clamps that have the correct width of band. Perforated hose clamps are not as secure.

[Qwodracer]

Riding the moto only 75 miles per year also contributes to the problem. Have you followed the steps in the troubleshooting guide in the Repair Guidance section, or is that also something you've already done but not indicated yet?

The guides seem nice but whatever I’m chasing is not all the time. I only have issues sometimes when I stop at stoplights or encounter traffic and cant keep the rev over 5k, but sometimes it’s fine. Everytime I read the guide I come up with something else to replace and it never fixes the issue. 🤷‍♂️ The problem had gotten so bad that the bike wouldn’t even run, hence why I gave up and didn’t even touch the thing for 3 years.

I’ve had BMW cars and never had this much of an issue with them, I’ve done headgaskets, setting the vanos, and diag the electronics on the cars. for some reason all makes more sense to me than this bike does. I’ve never had a bike before, still don’t even have my license everytime I was supposed to do my road test this bike would not work, so I’ve had to cancel. I’m legit scared to drive this bike outside of walking distance from my house.

I want to get it sorted so I can get my road test scheduled.

[Laitch]

The guides seem nice. Everytime I read the guide I come up with something else to replace and it never fixes the issue. 🤷‍♂️

What do you mean by the guide is nice? Have you verified the function of both the fuel injection control unit and the ignition control unit by checking their outputs according to the test data? Have you reviewed BMW's K Model troubleshooting guide on the site and tried to develop data on your units from them?

The purpose of the guides is to provide tests that verify the function of components, not inspire shopping. 

[Qwodracer]

What do you mean by the guide is nice? Have you verified the function of both the fuel injection control unit and the ignition control unit by checking their outputs according to the test data? Have you reviewed BMW's K Model troubleshooting guide on the site and tried to develop data on your units from them?

The purpose of the guides is to provide tests that verify the function of components, not inspire shopping. 

The modules tested fine in 2017. I even bought a second ignition module used to test as well, same results. The guides aren’t helpful one bit when it comes to an intermittent drivability issue.


So I just now
Cut the clamps and removed the TBs

There was dirt under the flange on the center one, so cleaning everything up and I ordered new screw clamps from some euro bike website. Hopefully that was the issue of why the screw was not adjusting the vacuum. Have a parts cleaner at work so the TBs will be getting dunked in there.