Still Running Rough below 4000 Revs !

[Roger Chatterton]

Please, I am now struggling for a solution -on my Purple 100GS PD -1994.

Not made it to the Belgium Rally 'cos my Turquoise PD has a missing main bearing locator pin, and is with Mr Scriminger.

So, was planning on using my Purple PD , but oh no ....it's running like a kangaroo- very jerky on falling throttle below 4K revs; runs a treat above 4K.

So far -

checked timing -good
checked compression -good to excellent
replaced spark plugs, plug caps and HT leads
replaced carb diaphragms
squirted copious amounts of carb cleaner into carbs with engine running
Balanced carbs as best I could

Still running rough and jumpy.

However, one clue seems to be that plugs are really sooty/dry black, but this might be due to having to run at idle speed into road to my lock up ?

I am now going to check mixture settings again, and clean out the pilot jet with more cleaner.

Any suggestions please, as timing is fine, so unlikely to be bean can or hal sensor, and compression is good, so unlikely to be burnt exhaust valves, and bike runs great at higher speeds.

Two possibles though, as I am unsure as to what symptoms of a faulty Ignition Control Unit might be, and secondly, my bike still has the secondary air circulation system fitted, which I want to remove, but can't find a suitable "blanking - off" cap for the threaded outlet under the exhaust front pipes (16mm - 1.5 mm pitch ?).

So, sorry not to join with the guys in Belgium, and no Belgian beers for me then

 

[cookie]

choke stuck on?

 

[Roger Chatterton]

Replaced the choke return springs too, and choke
retracts just fine. So unless something inside the choke
mechanism can stick, then din't think it can
be choke sticking. Sufficient slack on cable at the carb as well!

 

[cookie]

i think my next step would be to strip the carbs and clean.

 

[Roger Chatterton]

Cookie,
never stripped carbs down before, and think I might screw it up a bit -isn't there someone on here who does ultrasonic cleaning ? Would like to get bike sorted asap, as I've not had much luck bikewise of late !
However I have just taken out the idle jets, and given those a good clean, but not really made much difference.
Next job will be to give the K&N filter a thorough wash - something has got to be making the plugs so black - not burning any oil, and not excessive smoke from the exhaust. Have adjusted mixture back to the stock setting of 1 full turn out, as a starting point, and still black plugs.

 

[NeilDD]

Roger
Give me a call tomorrow afternoon (after 1400) on 0 1 7 6 3 2 6 0 five nine 5
I've got a U/S cleaner and various solvent we can try

Neil

 

[Roger Chatterton]

Thanks Neil - will do ! Where abouts are you based ?

 

[NeilDD]

Melbourn

I'll be at the Silver Ball south of Royston on the A10 till about 2, so any time after that should be OK

Neil

 

[Roger Chatterton]

Well, there's a stroke of luck - I live in Cambridge ! Often go to Silver Ball for a breakfast.

 

[chriswilliams]

Ill be interested to see what you find as i have the same symptoms
Thanks
Chris

 

[FatAl]

How many miles has it done? I'm sure I read somewhere that a worn timing chain and tensioner can affect the smooth running of these engines.

 

[Roger Chatterton]

Hi Fatal,
as mentioned in my first post, timing has been checked and appears to be dead on.
Bike is low mileage, around 15K on German speedo or similar, and just 10K on English speedo.

 

[Roger Chatterton]

Ill be interested to see what you find as i have the same symptoms
Thanks
Chris

Hi Zednine,
don't be shy - what steps have you been through to try and cure the rough running problem ? Be interested to know as it might be of help to me or to anyone else on here with similar dilemma.
Roger

 

[chriswilliams]

Hi Zednine,
don't be shy - what steps have you been through to try and cure the rough running problem ? Be interested to know as it might be of help to me or to anyone else on here with similar dilemma.
Roger

Hi Roger

I have a Mystic which has been stood a while before bought it so I assumed the rough running was gummed up carbs .... 4 strip and cleans later and im pretty sure the carbs are spotless ... It starts 1st time and runs but feels rough and on runs it will soot up one plug
Air filter is fine and tappets and end floats are perfect ... Im a bit stumped
Chris

 

[Roger Chatterton]

Hi Roger

I have a Mystic which has been stood a while before bought it so I assumed the rough running was gummed up carbs .... 4 strip and cleans later and im pretty sure the carbs are spotless ... It starts 1st time and runs but feels rough and on runs it will soot up one plug
Air filter is fine and tappets and end floats are perfect ... Im a bit stumped
Chris

Hi Zednine
have you checked your plug leads and caps?- if it's just on one side, it could be a poor spark, or possibly the coil. My problem is on both plugs, and nothing I have done so far seems to have improved matters much.

I am going to get my carbs Ultra cleaned, thanks to a kind offer from a fellow tosser. Will see if that nails the problem !

 

[jimish]

You say you have checked the timing, but have you checked that the automatic advance is operating correctly i.e. advancing fully which it probably is because it runs fine at 4000rpm but is it returning when the engine speed reduces? The advance weights can stick and should be lubed periodically

Also check that you haven't got any air leaks between the carbs and the inlet manifolds.

Might be wrong, but just a couple of thoughts. Good luck with it, and let us know what fixes it please.

 

[cristhemuso]

Hi. I suggest check for induction leak. Spray wd40 or "easy start" around carb rubbers. If there is a leak engine will race. Also whip off the float bowls, remove main jet and emulsion tube and check the jet holder is not all gunked up with rusty crap from the inside of the tank. My old GS needed cleaning out regularly. Filters dont seem to help. Main symptom is rough low speed engine. I have plastic PD tank now and no problems. Take care putting main jet back in. You might have to take top of carb off and extract needle. Whole job will take half hour max.

 

[Roger Chatterton]

Hi. I suggest check for induction leak. Spray wd40 or "easy start" around carb rubbers. If there is a leak engine will race. Also whip off the float bowls, remove main jet and emulsion tube and check the jet holder is not all gunked up with rusty crap from the inside of the tank. My old GS needed cleaning out regularly. Filters dont seem to help. Main symptom is rough low speed engine. I have plastic PD tank now and no problems. Take care putting main jet back in. You might have to take top of carb off and extract needle. Whole job will take half hour max.

Hi Chris,
thanks for the reply, but I emphasise again, that problem is NOT too much air in mixture, it is black sooty plugs, which indicates one of two things;
either -
insufficient air,
or
very weak spark/fuel burn

As also mentioned, I replaced the carb diaphragms, and removed float bowls - they were immaculately clean ! I also have the plastic tank.Have cleaned idle jets, which are far more likely to be the problem as bike is jerky BELOW 3-4000 revs- above this it runs like a rocket ! Idle jets control running at lower revs.

My conclusions are now veering away from carb/fuel related, and in the direction of my alternative conclusion, namely -weak spark.

Removed the coil, ( and had to spoil the new plug leads I just made as the brass cup type retainers into coil were stuck).

Coil readings are not as they should be, if I have understood Haynes and Clymer properly, on the "Dual" coil ( 2 coils in one unit type) -

Primary = 0.8 Ohms
Secondary = 12.5 Ohms.

So, does this mean my coil is on the way out ( ie giving a weak spark at lower revs) ? Or could it be the ICU (ignition control unit) ?

My ICU is the Telefunken version ( with a BMW logo on it !!!
Ref No 12.14.1244.477

Any conclusions ....please ?

Finally - where can I get hold of the brass "cup" bits that solder onto the HT leads at the coil end of the leads ?

Very finally - if I get hold of an early K100 coil, which is suitable replacement apparently, does it involve much buggering about to fit in existing location on the frame - I do not have mains power in lock up to enable drilling frame etc -

 

[cristhemuso]

I sense your frustration Roger. If coil is grey original type then look very very closely. They all fail eventually with a hairline crack. Take it off to find the crack. When the weather gets damp the ignition gets really bad with misfires. The replacement I bought was completely different design and fine afterwards. (might have been K series not sure rings a bell) Check you are using exactly the correct temperature grade plugs. Best to check everything now. You need to take the main jet and tube out to find the crap. Float bowls can be clear with a load of dirt in the taper seat. (Dirt means poor mixing of fuel and air at all revs). Check needles are correct taper and on correct clip. I have tried making up plug leads and caps in the past. Never satisfactory. I strongly suggest you buy the proper moulded ones from bmw/MW (cheap). I think there is some voodoo resistor in them. When I used OEM it was much better. NGK caps never worked correctly.
Thats all for now. Good luck.

 

[Rob Farmer]

Roger,

I'll be very surprised if it is your ignition module but if you want to check it out I can either lend you one or test yours out with my module tester.

Have a look down into the carb from the air filter end and make sure the slide sits right down on the bottom of the cutouts. I had a similar issue where the I rings at the top of the slide had swelled up, presumably with the effect of modern fuel. Mine had swelled so much the taper on the needle was exposed, felt like I was on choke all the time. New o rings cured the problem.