Damn. Still dealing with high idle

[svejkovat]

Does my '83 R65 have an a mechanical advance under the beancan?

I've rebuilt the carbs and was sure that the problem had vanished.  I'd even put a few mid range trips in with no problem.   Yesterday I took the highway about 20mi out of town and when I reached the next city the idle would not return below 3000.  I can jog it down by bumping the clutch.

It will behave, it seems, all day long in city traffic.   10 minutes at 5500 rpm and when I stop for the next light it idles at 3000.   Takes a while to return to 1200 and is irritating to ride since it essentially has no downshifting brake and changes the feel of riding. 

Mechanical advance?   Lube the mechanism?  Replace the springs?   No mechanical advance on my bike?  What to check next then?

[mrclubike]

The mechanical advance is in the lower half  of the Bean Can

I don't think a sticking advance can cause a 3000 rpm idle
Easy enough to check the timing with a timing light

I would look at a sticking throttle plate in the carb
Did you replace the O rings on the throttle shafts

[Barry]

What hot idle speed do you have the carbs set at ?

If above 1000 RPM do a simple experiment:

Lower the idle speed by backing off the idle stop screws equally both sides and see if it has an impact on the problem.

[svejkovat]

Haven't been able to look into anything yet today.

I rebuilt the carbs a few hundred miles ago and it's been running like a top.  Very strange then that it's suddenly exhibiting similar to just before the rebuild.

I did not replace the butterfly orings.  The orings elsewhere were in very good shape and the engine is low mileage and has always been well stored.  I replaced all other orings.  I don't think this oring could be a culprit judging by the very conditional nature of the problem. Could do a simple test of this by supergluing an oring outside and snug to the body.

I wonder why, specifically, high idle is a problem only after spending five minutes or more at high rpm.  Can run around town all day long... no problem.  Take it out on the highway for a good fast 10 mile stretch.  Idle sticks at 3000.

What has me especially worried is if this indicates a way too lean condition happening when I'm at speed on the highway for some reason. 

I did find some chafing marks on the steel cylinder of one of the diaphragm carriers during the rebuild. This cylinder is aluminum and the shaft it slides on is stainless steel.  The chafing likely had a little aluminum build up that I honed off with scotchbright. 

I'll go back into the diaphragm carriers/dampers and see if it's reappeared.  If so this would make perfect sense of things.  If I have to reclean/rehone some chafing off again I'll look into adjusting the alignment of that diaphragm.

I may invest in a couple of mikunis some day after all

I'll report back in any case and thank you for the suggestions.

[mrclubike]

The problem with the throttle shaft Orings is they  swell and cause the throttle shaft to stick
You have to grind the peened over screw off of the throttle shaft  to remove them and refit new screws during reassembly 
That is why they never get replaced

Remember it takes very little throttle opening in neutral to get a higher idle

[Kelvin]

I'm wondering if one of the carburettor pistons is jamming open. You go out at high (engine) speed for a bit, the piston rises. You close the throttle and one of the pistons jams high. The intake sucks mixture from the idle circuit, but also from the main circuit, that would normally have the main needle blocking flow.

It's unlikely that this would happen in both carburettors simultaneously, so: 1) is it a rough idle, driven by one cylinder? And, 2) if you tap the carburettor body with a small hammer to un-jam the piston, does the problem rectify?

The lazy cylinder has noisier tappets, start by tapping the carb on the quiet side of the engine.

[Justin B.]

If the idle is too high after getting off the freeway, come to a stop, apply brake, then ease out the clutch and bog the engine down.  If the idle returns to normal then it's likely the advance mechanism is sticking. 

Yours are the exact symptoms our '80 had with a sticky advance.

[SoloLobo]

Check that your chokes are not sticking partially open.

When you experience a high idle, push down on each choke lever to see if it is bottomed out.  If not, that may be your problem.

[svejkovat]

If the idle is too high after getting off the freeway, come to a stop, apply brake, then ease out the clutch and bog the engine down.  If the idle returns to normal then it's likely the advance mechanism is sticking. 

Yours are the exact symptoms our '80 had with a sticky advance.

Sorry for such ignorance.  I thought I knew my bike better. But it's confirmed then that I have a mechanical advance?

I have yet to take off the 'bean can'.   I've been pretty busy.  I will tonight.  I've read alternately that one or both, sticking fly-weights and/or weak springs, may be the culprit.   

??

I'll go in and check, free things up, lightly lube, and report back.

[BPT]

In our range of years, the bean can was kind of a hybrid.  It has the electronic Hall sensor but still has the mechanical advance part spinning around in there.  That's where the things can get stuck or the springs stretched.  So maybe that can help with some of your confusion?

It's a pain to get the can completely apart.  You can see (kind of...) the parts talked about here through the little oval hole.  That cap isn't sealed but could be difficult to pop off if it hasn't been for a while (I slide a razor blade under the lip to get it started, the metal is a bit soft).
You have to be careful with lube here.  Some say don't, but guys here have said to use it very sparingly and use the proper stuff.  If you use the wrong kind or too much, it'll fling all over and cause more problems.  Through that little window though, you might be able to see if there is any obvious corrosion or something else causing them to stick.

If you haven't already, search here or Google "bmw beancan disassembly" or something similar and you'll be able to see where all the parts are.

[tunnelrider]

I've read alternately that one or both, sticking fly-weights and/or weak springs, may be the culprit. 

??

I'll go in and check, free things up, lightly lube, and report back.

I think you're looking at the right spot, as Justin said with his '80 and I had with mine last year, same symptoms.  Playing around with the fly weight spring tension by pulling up the spring anchor maybe 1mm each spring, increasing the preload of the spring, worked for me.  You can actually do this through the oval inspection hole with the bean can off the bike if you know what you are looking at, would save having to take the bean can apart. Like BPT said, by looking at some pics of a disassembled bean can you can get familiar with the insides.

But reality is I took my bean can apart twice before I was familiar enough to make the right adjustments.  First time I put new springs on but ended up going in again, putting the old ones back on and increasing the preload a little. 8K km later it's still working OK.

Spraying some lube in at the fly weight pivots through the inspection hole should make some difference if sticky weights and/or weak springs are holding up the revs.  I used a liberal amount of CRC556 and light oil initially, then tried chain lube, all which made some difference to dropping the revs.  You can drain the excess by unscrewing the bottom Phillips screw on the outside of the case, on or off the bike. But this never made my high rev problem go away completely, I had to adjust the spring anchor posts.

[Justin B.]

In the case of the '80 they were rusty and nothing in the advance mechanism worked freely.  I had to disassemble, clean, polish pivots, lube, and reassemble.  Not really hard but "fiddly" as our Bros. across the pond might term it.

[nhmaf]

Indeed - you may want to do some of the disassembly in a clear plastic bag as there are a couple small parts that like to shoot out and get lost.   Somewhere around here I thought I had some instruction from an internet site (now apparently unreachable) about R&R for these things... will look some more for it...

[nhmaf]

In meantime, I've found some merged threads covering this topic from earlier forum discussions - has quite a bit of info and disassembly pics.  I cannot attach it here as it is too big (4MB).  I will see if I can put it on dropbox or something, or else PM me your email address and I can try to email it

[svejkovat]

Can you guys confirm that timing advance 'stickage' whether from weak springs or sticking weights can cause an increase of 2k? I've read elsewhere that it cannot.  I'd like to ascertain this before completely rebuilding the beancan.  Also, this is clearly associated with operating temperature and only AT full operating temperature.  How would this apply to the timing advance?  This is really driving me batty.

I removed that can's inspection plug and administered to all moving inhabitants with "CRC 2-26 precision electronic lubricant".   No noticeable improvement.  (just rebuild the damn can and quit pulling hair fercrissakes brad and then get back to us awreddy)

I've struck the diaphragm domes with a blunt object when it's at high idle.  No avail. 

I've closely inspected the linkages and cables at high idle.   Both choke and both throttle are pegged at zero.   No avail.

It was just suggested elsewhere that my intake valve clearances may be off.  But the fact that I can bump the idle down with the clutch would seem to belie this.  No?

The high idle is so smooth that it suggests both cylinders are in sync. So that likewise belies any problems originating with either one carb or valve.  (agin.... the timing advance... what do we have to do to convince you boy?)

This ONLY happens at operating temp.  Let the bike cool down.  Idles fine.  At operating temp I can come to a stop, clutch the idle down from 3.2 to 1.2K (where I have it set 'normally') and then blip the throttle back up to 4K and the idle 'sticks' again at 3.2k.  Let the engine rest/cool for 30 minutes and it idles fine.

This is ruining what is left of my summer riding.

...and my go-to fun ride, the 50cc '84 Puch is likewise driving me nuts.  Runs like a champ but is balking (again, only when warmed up) at high rpm.  No change in timing, carb cleaning, plug replacement, points replacement, condenser replacement,  main jet,  idle setting, coil replacement, decarbonization of ports and pipe, etc seems to fix it. Yeah, done it all. It occurred suddenly a while back so it's not likely to be cylinder or seal wear or gasket leakage.

I'm 57.  Anyone else here ever started to wonder if middle age has sapped a little of the fun out of tinkering to keep these vintage machines alive?  Or am I only in the middle of a bad spell of gremlins?   I realize that happens. But this time it's more than commonly demoralizing.

 I'm an accomplished enough mechanic that dropping a bike off at the dealership for 300 dollar repairs just seems about as much like giving in and giving up as selling off and getting a relatively hassle free 2018 model.  I can easily afford professional repair and/or new bikes in fact.  But till recently I've always put a very high value on, and been rewarded by, the bond established with these older machines through intimate knowledge and repair of them.

But I have to say it's flagging.

sorry for the massive, messy, sometimes meandering missive... and thanks for listening.