Hesitant after diaphram change!!

[beemer]

I recently changed my carb diaphrams on my R65LS 83 model and now she just won't go past 60mph!!!feels almost like fuel starvation,plenty of fuel flow,checked valves clearance,plugs,ignition coil seems fine,i have a spare coil so changed over just incase,bike starts and idles fine,help and advice please,thanks.

[wilcom]

Take your finger and lift each slide and feel the suction/vacuum.  Do they feel the same? May have a leak on one of them. I had one tear on a trip and she wouldn't run at all, idled like a champ but wouldn't take any throttle at all.

Good luck

[Bob_Roller]

By chance did you purchase 'pattern' parts from Motobins ?

A few of the UK members on this forum installed them and the thickness of the diaphragm caused problems, can't quite remember what they were .

I'm sure they'll post a response tomorrow .

[nhmaf]

Yes, there are "non-Bing" replacement diaphragms that are the same overall shape but the rubber is definitely thicker and stiffer - these have caused issues with a number of folks.  Also, be sure that you have them properly oriented/seated with the small tab going into the indented are on the inside edge.

[beemer]

Yes these are the "non bing"type,can anything be done?or do i have to replace them?thanks.

[montmil]

Yes these are the "non bing"type,can anything be done?or do i have to replace them?thanks.

Perhaps ask Motobins for a full or partial credit with an exchange for the "real" Bing diaphragms. The thicker rubbers will likely be problematic for, oh, forever. Sometimes pattern parts work just fine.

Monte

[Lucky_Lou]

Yes these are the "non bing"type,can anything be done?or do i have to replace them?thanks.

I was one of the folk with trouble with these only fit Bing originals the generic ones are cr*p especially troublesome if you have the flat top carbs. Also check the rubber connector to the heads have been properly refitted.
Lou

[Barry]

On the one hand you have to wonder why Motobins and others continue to sell the generic diaphragms if they are so bad.

On the other hand you have to wonder why the thicker rubber makes so much difference when the old Stromberg and SU type CV carbs used to deliberately add damping with an oil dashpot.

Thankfully I've not had to replace mine yet.  

[nhmaf]

The Bing CV carbs works on substantially lower vacuum (pressure? or rather suction) than other CV designs from Mikuni, Keihin, etc.  The thicker rubber is certainly stiffer/ less pliable as has been demonstrated with testing deflection while applying specific weights.  The relative differences in overall carb vacuum is especially apparent when I am working on my Japanese motorbikes and my BMW airheads with my Morgan Carbtune (rotameter).  One has to stand the carbtune upside down and let gravity assist the steel slides' movement when working with the bings - this makes the rotameter's full scale reading approximately 20 mm/HG, whereas in its normal position full scale is closer to 200 mm/HG units, which is what I use with the Kawasaki's carbs.

Just get the bona-fide Bing rubbers and you'll be happier!

[Rob Valdez 79 R65]

Dome-tops also may or may not have a return-assist spring (#7).
If you have these in your carbs, try removing them and see what effect that has.


http://www.realoem.com/bmw/showparts.do?model=0364&mospid=51897&btnr=13_0462&hg=13&fg=05

I saw a pair of R100 dome-tops just this last weekend taken apart, and there were no springs in them.
The bike ran fine.  (Bing diaphragms)

[montmil]

On the one hand you have to wonder why Motobins and others continue to sell the generic diaphragms if they are so bad.

An old saying from P.T. Barnum, of circus promotion fame; "There's a sucker born every minute."

Prior to rebuilding the Bings on my 1981 R65, I did a lot –and I mean A LOT– of internet research on how to do it and how not to do it. The knock-off Bing diaphragms were noted as to be avoided like the plague.

Monte

[beemer]

Well according to them these are fine and they haven't had any problems with them!!so you have to take their word for it i guess,why doesn't it show up being hesitant when you just rev the bike?i guess it has to be under load,ie,when your on the move.

[beemer]

Dome-tops also may or may not have a return-assist spring (#7).
If you have these in your carbs, try removing them and see what effect that has.


http://www.realoem.com/bmw/showparts.do?model=0364&mospid=51897&btnr=13_0462&hg=13&fg=05

I saw a pair of R100 dome-tops just this last weekend taken apart, and there were no springs in them.
The bike ran fine.  (Bing diaphragms)

Thanks,i will try this.

[beemer]

Yes these are the "non bing"type,can anything be done?or do i have to replace them?thanks.

I was one of the folk with trouble with these only fit Bing originals the generic ones are cr*p especially troublesome if you have the flat top carbs. Also check the rubber connector to the heads have been properly refitted.
Lou

which rubber connector Lou?

[Rob Valdez 79 R65]

which rubber connector Lou?  

#3


http://www.realoem.com/bmw/showparts.do?model=0364&mospid=51897&btnr=13_0455&hg=13&fg=05

That HAS to be an air-tight seal.  It can be checked by spraying carb cleaner on them while the engine is running.  If the RPM's rise, you know you have a leak.
The rubber gets hard over time and can even crack.  Best to replace them every 10 years or so.