One down, one to go (I hope!)

[boxer54]

It was lumpy and hesitant when I gently turned the throttle then would suddenly surge

Do you mean suddenly run healthily?

What happens when throttle backed off again?
What happens when throttle is increased past where the engine 'surges'?

I'll try to be more clear in what I meant by 'surge'.
When I gently twist the throttle, the bike would hesitate. There would be a increase in engine revs, but insignificant like a fuel starvation? timing? not sparking? But then after the hesitant, it would ignite/ spark/ suddenly catch and we'd be off running better. Past the surge the engine is still not running right.

When throttle backed off to lower RPM the 'struggle' returned.

I intend to do a timing check, a plug chop and ride more like a drunk mammal

[PITAPan]

It was lumpy and hesitant when I gently turned the throttle then would suddenly surge

Do you mean suddenly run healthily?

What happens when throttle backed off again?
What happens when throttle is increased past where the engine 'surges'?

I'll try to be more clear in what I meant by 'surge'.
When I gently twist the throttle, the bike would hesitate. There would be a increase in engine revs, but insignificant like a fuel starvation? timing? not sparking? But then after the hesitant, it would ignite/ spark/ suddenly catch and we'd be off running better. Past the surge the engine is still not running right.

When throttle backed off to lower RPM the 'struggle' returned.

I intend to do a timing check, a plug chop and ride more like a drunk mammal

Surge = you don't do much of anything and the bike surges ahead. Rare in airheads, common in later models.

Hesitation = you do a small something (throttle) and the bike hesitates then gathers itself together and goes. maybe a pretty tiny effect but noticeable. Not normal.

lag = yuo do a big something (whack it to half throttle) and the bike has some lag (lazy hesitation) in response. Normal with CV carbs.

Story telling example:

"So I'm riding down the street at about 2000rpm in first and when I just open the throttle the bike hesitates a moment then goes. I had set my timing to 3 degrees at idle (correct would be 6 degrees) to see what would happen. When I set it back to 6 degrees the hesitation went away."

True story BTW and I don't know what your timing is supposed to be set to.



What kind of emission plumbing do you have on this thing? (Hint: "I don't know" is wrong answer )



For plug chops I carry a big spark plug wrench and boot puller from the shop, a few sets of clean plugs and a pot holder from the kitchen (those things are HOT).

[chasbmw]

I suffered from poor low speed running and surging on my 90/6.

It was cured when I replaced the O rings on the throttle spindles. I had not done this when I had rebuilt the carbs earlier.

[boxer54]

A brief update...
I have been unable to get out on the bike over the last week due to work but tonight I got a chance to get a look.
It started easily and sounded fine, with no hesitancy etc. I decided to take it out and have a 'feel'. It ran sweetly and pulled sweetly. I gave it a blast and it seemed to be running fine; no misfire, no surging etc. I'll be taking it for a longer run tomo and intend to do a plug chop and will get back.
Cheers

[boxer54]

...So with a break in the weather over here I managed to spend some time with my toolbox and the Bike today.

The bike is still running rough intermittently but I am sure, it is NOT fuel or air related. I think it is electrical.
After extensive reading and re-reading and re-reading on this site on ABC and Snowbum's site, I am leaning toward two things. Either a faulty coil (I have two...dual plugged) or a dodgy ignition kill switch. http://bmwmotorcycletech.info/Ignition.htm

I did an ignition sensor test today (the 'bean can') but I am not 100% that the test was accurate (first time nerves) as I could not find the 3pin plug mentioned everywhere. Rather I have three individual wires, green, red and b n' w, trailing off toward the control Unit. After disconnectiong all three wires, I attached a spare piece of wire to the middle/ red wire, unscrewed and replugged and secured one spark plug the the cylinder head and with Ignition 'ON', I earthed the spare cable...Nothing. I am led to believe that, considering the test was accurate, it should spark. That it didn't spark means I have faulty coil(s) or ICU. I intend to test coils ASAP.

I will also be renewing my heat sink paste.

The reason I am leaning toward electrical rather than fuel is two fold.
1. The BMW specialist mechanic timed and tuned the bike and it was running fine for a while.
2. Snowbum's site describes my symptoms to the tee; "...typically will idle OK, but won't raise its rpm up properly. This problem acts somewhat similarly to a hole in the carburetor diaphragms. The actual problem is a poor ignition kill switch at the bars."

So, with new found eagerness, I attempted to have a look inside kill switch to see if I could establish, from my new found electrical experience, a way to bypass the kill switch to eliminate that problem...Without consulting the manual I soon realised I had opened the throttle cable canister rather than the switch. Things went 'ping' and a little chain went slack and the throttle grip nearly slid off the bar. Into the deep, the best way to learn. I managed to get it all back together but alas, as I silently suspected, when I started the machine, the revs were WAY UP So, any guidance here would be brilliant too (am I infiltrating my own thread with a different topic??)

To sum up for now....I understand there are often more than a few ways to say or call something related to mechanics, or anything for that matter, and I am looking about and learning; but some terminology as a newbie I can't understand....

'Emission plumbing': I'm leaning toward exhaust, right...??? If so, its stock...
'Carb circuits'/ 'low throttle circuits' : Are these an electrical wires controlling the carbs function somehow??

I feel so much closer to the machine
cheers

[Ken in Oklahoma]

There is a sort of easy way to handle that potential kill switch problem. Simply hot wire the battery positive to the positive side of the coils. That bypasses a bunch of wiring. If the bike runs fine that means something is wrong somewhere, but at least you know that the bike can run right. And that knowledge will help you devise better theories as to what can be wrong.

Editing: You would then have to kill the engine by putting the bike in a high gear, idling, and simply let out the clutch (with the front brake on so the "jump" will be minimized).

Be careful bench testing coils. A bench test can prove a coil bad, but it can't prove it good. At some point in your trouble shooting you might want to buy new coils. I know that is expensive, but some of us, including me, keep a couple new coils in stock. The chances are, sooner or later, you are going to need new coils anyhow.

Ken

[Major Softie]

Ya, coils deteriorate with age. They are not a "work or don't work" kind of part. Old coils never work as well as new coils.

[jagarra]

Coils can be a PIA to diagnose. Had a bad one in a car that would start to fail and make it misfire after about 25 minutes into use. Started and ran perfect until that point. Sometimes you have to just change an item to eliminate it as a potential problem, because it never fails completely to provide a solid fault.

[Major Softie]

Coils can be a PIA to diagnose. Had a bad one in a car that would start to fail and make it misfire after about 25 minutes into use. Started and ran perfect until that point. Sometimes you have to just change an item to eliminate it as a potential problem, because it never fails completely to provide a solid fault.

I always assume that behavior is a failing coil if it happens on a carbureted bike with points ignition. It's harder on more electronic bikes (or cars) because there are more components that can heat fail that way.