Revs not returning on R65

[Hunsta]

OK have a small problem with my 1984 R65. After the bike is well and truely warmed up the  revs seem to stay very high and will only return to idle speed when the motor is laboured. It will also climb up to 2500-3000rpm`s by itself if the throttle is slightly touched.
 Now Ive had the diaphrams renewed,and the inlet rubbers renewed about 6 months ago. The hoses to the air box is aslo secured properly. The throttle is returning properly as well as the cables to the idle stops on the carbies and also the choke cables as well.
 Now Ive been told that it may be the weights in the beancan. However I dont think this model has those. Im not overly mechanical, so Im not sure what to do next. However Im not total backward with the spanners. Could it be the slides or the needles sticking or something like that. But what would make in increase revs on its own.
 Anyone have any ideas what the problem could be, as its really giving me the irrits
 Cheers
Craig

[Barry]

This is a regular topic on the forum so you will find lots of info from a search.

The beancan does have a mechanical advance mechanism and there are tales of it sticking and that would cause your symptoms but don't assume this is the problem until you have eliminated the simple things.

First off make sure the idle speed is set when fully warm.  This is the most likely cause of your problem.  

There are tests you can do to check if it's the advance mechanism sticking. Basically you need to check the ignition timing with a strobe to make sure it returns to the static setting of 6 deg BTDC at idle.

If you conclude its sticking The bean can mechanism can be lubricated with light oil by removing a small oval plate on the side.

  

[drewboid]

Yes - typical problem of sticky weights in the mechanical advance mech.  I have had success using the Omega electronic ignition modules that mounts to the crank.
there is also a new electronic beancan available.

Or you can try to lubricaate the weights - if the bearing parts are not badly worn that will restore proper action. YMMV - good luck!

[Bob_Roller]

Performing a carburetor synchronization, without the engine being up to operating temperature, can cause similar symptoms .

[nhmaf]

+1 to all of the above - try a re-synch of the carbs AFTER you 've taken the bike on a good ~ 25 minute ride and have it fully warmed up.   These symptoms do happen if the carbs weren't properly synched when the engine was fully warm.  Also, just check over your carb boots and make sure that there isn't a pinch or leak, especially between the carb and cylinder intake.  I would also just check the valve clearances before attempting to re-synch the carbs, as they have a big impact on the carb synch too.   If the above fails to correct the problem, then it is time to go in and consider the bean can.  

There is another test that sometimes works to check if it is the advance weights inthe bean can sticking - but isn't always definitive:   IF the engine revs up above idle to 2000 or 3000 rpms just sitting there and you ARE NOT TOUCHING the throttle, hit the kill switch on the right handldebar.    Then, return the kill switch to normal RUN position, and WITHOUT TOUCHING THE THROTTLE, press the starter to restart the engine.   If it immediately revs back up again to 2000-3000 RPM, then the weights are very likely sticking badly.  If it doesn't immediately go up to those RPMs, they still might be somewhat sticky, and the sudden decel of killing the engine brought them back to normal position, or there could be a carb issue still.

[montmil]

Confirm the throttle cables are properly routed and adjusted to spec per the manual. Cable tuning begins at the twist grip, not the carbs.

Monte

[Hunsta]

There is another test that sometimes works to check if it is the advance weights inthe bean can sticking - but isn't always definitive:   IF the engine revs up above idle to 2000 or 3000 rpms just sitting there and you ARE NOT TOUCHING the throttle, hit the kill switch on the right handldebar.    Then, return the kill switch to normal RUN position, and WITHOUT TOUCHING THE THROTTLE, press the starter to restart the engine.   If it immediately revs back up again to 2000-3000 RPM, then the weights are very likely sticking badly.  If it doesn't immediately go up to those RPMs, they still might be somewhat sticky, and the sudden decel of killing the engine brought them back to normal position, or there could be a carb issue still.

OK Ive tried this method yesterday after riding home from work(30min ride). It did start back up at normal idle speed, but the minute i slightly touched the throttle it started to climb again. Can anyone give me a rundown on how to get to and lubricate said weights. Will it require retuning after this? Better still is there a link to this work in this site?
 Cheers
Craig

[Bob_Roller]

There's a small oval shaped pressed sheet metal plate that you can pry off with a small screwdriver, then spray in the lubricant of your choice, then replace the metal cap .

[Hunsta]

There's a small oval shaped pressed sheet metal plate that you can pry off with a small screwdriver, then spray in the lubricant of your choice, then replace the metal cap .

OK now at the risk of sounding really dense here, Firstly lets establish that the ignition trigger is aka "the Beancan" right. This plate you speak of, is this the one screwed to the front of the can?
Secondly the weights which is being spoken about. I`ll just read what it says in my Haynes manual.

"The igintion system fitted to all BMW models from 1981 onwardss is a transistor-controlled type which contains no mechanical components other than a centrifugal advance and retard unit mounted in the trigger assembly." As Ive already stated its a 1984 model.

This "centrifugal advance and retard unit" is this the part that need lubrication.
 Sorry for sounding like a complete mechanical dumbass, but I dont want to start taking the wrong bits apart.
 cheers
Craig

[Barry]

The advance mechanism is located right at the bottom of the bean can so the small oval plate is on the side of the bean can towards the back.

It is possible to dismantle the beancan but it is not for the faint hearted and can be seriously expensive to repair or replace. You really need to be sure this is the problem before delving in here.

Have you tried to reduce the idle speed a little yet ? It takes seconds costs nothing and there is no risk.

[montmil]

Hunsta, Might you be related to my college-days Italian bike riding buddy from Germany, Aprillia the Hunsta? Likely not...

Anyway. Yes, the "bean can" is the Ignition Trigger Unit located under the engine's front cover. Do remove the negative battery cable before pulling the cover as it is possible to short out the diode board, thereby causing more problems than you already have.

Removing the bean can is easy. Disconnect the wire harness at the plastic plug, remove two Allen screws and lift off the ITU. It refits only one way due to the offset drive dogs so no worries about refit.

There is an oval-shaped metal cap/plug on the side of the can's body. Pry this off with a tiny flat blade screwdriver. Do not let it fly across the garage as finding it will be a chore.  

Peeking into the can's interior, you'll see the advance mechanism as you rotate the drive shaft. See the small, nylon "feet" that slide across the metal "floor"? Spot the small pins that the advance arms rotate on? This is the oft times problem area.

I use something like WD40 to rinse out the area. Drain this kerosene-like material out. An aerosol, non-drying, industrial lubricant (I use LPS-2) will keep everything sliding properly. Drain off any excess. All ignition components in the can are solid-state and you won't harm them during the lube process.

I have rebuilt several bean cans. It's a fiddly process but doable, with care.

You'll need to reset the ignition timing after replacing the can.

Monte

[nhmaf]

Yes, if you remove the bean can, make a reference mark on the edge of the can and on the engine case so you can get it very close to the original alignment to begin with.  Then it is minute amounts of rotation to fine tune if necessary.

[Hunsta]

Have you tried to reduce the idle speed a little yet ? It takes seconds costs nothing and there is no risk.

OK sprayed a little WD 40 last night and then took her for a ride this morning. No change, so I tried reducing the idle speed alittle and hey presto. Problem somewhat solved. It was on about 950rpm`s and I dropped it to 800rpm`s. This seems to have stopped the rev climb and it now returns to idle if not somewhat slowly. But it does return now.
 So now tell me. Why would having the idle speed up just alittle too high do this? (probably a stupid question to some) I run my DR650`s idle up high as this stops stalling in some  difficult conditions, but does nothing to the way the carbie preforms. Or is this just a Bing thing?
 Your in complete mechanical blondeness,
 Craig
ps just for the record. This is my first airhead.
 Ive had a R1100R and a R1200GS in my posession before. Its just the bing carbies are new to me.

[Barry]

The theory goes like this.  If ignition advance is increased the idle speed will also increase. (The stock 6 Deg BTDC is a compromise between easy starting and smooth idle).  

Say the idle speed is set at 950 RPM when the engine is not fully warmed up.  It will rise further with a hot engine and if it gets close enough to the point where the ignition advance kicks in you get this positive feedback effect which makes the idle speed rise even further. I'm only guessing here but Bing CV's may be more prone to this effect than others if the increased airflow also causes the carb to come up off its idle circuit.
 
Having said all that I wouldn't have expected this to happen with such a low idle speed as 950 RPM normally the advance mechanism doesn't kick in until around 1300 RPM although I guess this will vary a little.

I can only say that when I was new to BMW's I made the mistake of setting the idle on a warm but not fully hot engine and got the same symptoms as you.  For me a hot idle speed of approx. 1200 RPM was enough for this effect to kick in. After reading various forums  I then proceeded to dismantle clean and lubricate the Bean can. There was nothing wrong with it and the symptoms persisted.  I reduced the idle a touch and hey presto problem solved.

Now you can see why I keep pushing the "lower the idle speed first" mantra.

[Hunsta]

Now you can see why I keep pushing the "lower the idle speed first" mantra.

Well I can safely say that this is a mantra that I will keep well alive. And your theory on the subject sounds fairly sound as well.
 
 Cheers
Craig