BMW Question - Bing Carbs

[ohiorider]

At 128,000 miles, I had an excellent mechanic at my BMW dealer perform a 'top end' overhaul, which included Black Diamond valves, CC Products valve guides, and BMW valve spring replacement.  Also had rings replaced.  Retained stock pistons.  The bike initially exhibited a fair amount of vibration, which gradually grew less and less, to the point where I began using the bike as a daily rider again.

Now at approx 155,000 miles, the old gal has picked up another case of vibes (rpm, not speed related).

- I've balanced the carbs with an excellent balancing tool.
- timing is on the mark, and is now handled with an aftermarket solid state ignition that eliminates mechanical advance.
- tranny turns over smoothly with bike on center stand (so I don't expect tranny output shaft bearing failure)
- valves are adjusted to spec every 5000 miles
- plugs changed less than 1000 miles ago

I'm wondering if ..... it's time to rebuild the carbs again? And perhaps take an additional step.
- carbs were rebuilt at 110,000 miles (jets, needles, floats, o rings, diaphragms)

However ..... I got to thinking about the butterfly shafts and their bushings.  Maybe after all these years and miles, perhaps the bushings on these shafts are worn, and leaking air.  Anyone on here with Bing (or perhaps Dellorto) experience that can relate to this?

What's the best way to test for leaks?  I'm thinking spraying ether or starter fluid around the bushings to see if the bike idle changes when I do so.

[ohiorider]

Thanks for your thoughts on the topic, Kirb.  I'm thinking I'll contact Bing International and have them give me a quote on a complete carb rebuild.  I priced the parts on Max BMW site, and they're not outrageously priced (for BMW!)  Apparently, it's the o rings on the shaft that are often the issue, but to do those, it is necessary to deburr the screws (they're peened so they don't come undone) that hold the butterflies on the shafts.  The site showed new shafts and butterflies, and o-rings, but no metal bushings.  Apparently, there are none.

[arveno]

 http://vamotorrad.com/


Send them to Anton , very nice guy to deal with.
He’s  very knowledgeable on airhead BMW

[ohiorider]

http://vamotorrad.com/


Send them to Anton , very nice guy to deal with.
He�s  very knowledgeable on airhead BMW

Thanks for the reminder.  Anton has been working on airheads for quite a while.  It might be worthwhile for me to schedule a couple hours of shop time with him to look over the bike.  There's several items that could cause an old airhead to vibrate.  Would probably save me hours and $$ throwing money at the wrong problem.  Just checked GoogleMap ....... I could have a nice two lane ride most of the way over on old US 250 ..... approx 8 hours to his shop.  Think the old GS would be a kinder, gentler ride than my trip back from WV when I took delivery of my CB1100.  US 250 isn't in the best of shape due to the amount of heavy truck traffic supporting natural gas fracking.

[PeteS]

I had an '83 R100 and put 220k on it. I found in the later years that the ethonal gas was attacking the diaphrams. After a few years the slides would not rise in unison. I would swap them out before going further.
Early on I balanced the rods and pistons to within a few milligrams and also filled the handlebars with lead shot. All helped a lot.

Pete

[ohiorider]

I had an '83 R100 and put 220k on it. I found in the later years that the ethonal gas was attacking the diaphrams. After a few years the slides would not rise in unison. I would swap them out before going further.
Early on I balanced the rods and pistons to within a few milligrams and also filled the handlebars with lead shot. All helped a lot.

Pete

Pete. I don't know when the US started using a lot of 10% ethanol fuel.  I bought my R100GS in March 1991, and rode it for several years before having the carbs rebuilt (over 100k miles.)  But my early riding may have been before ethanol fuel was everywhere.  Funny thing is, this old GS was smooth as glass for years.  And many of them weren't.

Bob

[pressureangle]

A marginal lean condition will cause vibration too. See if shimming the needles up .020" helps at all.

[DAMMAG]

https://www.facebook.com/Boxerworks/videos/1998052913851333/

It's a Facebook video but it has some good tips.

[wirespokes]

The butterfly shafts don't run in bushings, just the carb casting. Rebuilding carbs isn't difficult, they're pretty simple devices really. It's possible to source the o-rings many places including McMaster Carr for considerably cheaper than Bing or BMW. It's criminal what they charge for those things! If you decide to rebuild I can help you find the sizes needed and where to order them. Mostly, a carb overhaul involves new o-rings, needle jet, jet needle, and perhaps diaphragms, besides all the cleaning. Only rarely have I needed to replace diaphragms or butterfly o-rings. In your case, I'd suspect o-rings first. 90% of the time that's all it is.

At what RPM range is it running rough?

Sometimes the cables can hang up, so don't discount that possibility.

Starting fluid or carb cleaner work well for finding leaks. Don't use brake clean - it can turn into a potent nerve gas when hot.

[rodekyll]

My kid had a lot of struggles with Bings on his R80/7.  He solved them with a pair of Mikunis.