Bing Flat Top

[BooG]

Never seen this type of Bing before. Anyone run with these? I'm about to rebuild them and try them out.

[Lucky_Lou]

They are the 79/80 model as fitted to mine they seem ok to me once they are set up. everything seems the same except the spring assist on the diaphragm.
Lou

[Barry]

I Have flat tops on my 79 except they have  truly "flat tops" not having that slight depression in your picture. Lou I think yours have that slight depression too. I doubt the difference is of any significance.

Flat tops were only used for 2 years which suggests they were a failed attempt at cost cutting and yet like Lou I have no problems at all with them once set up correctly. As Lou says they have no return spring for the slide which might have ruled them out for aviation use. Perhaps Bing decided to rationalise on the dome top design. Only other difference is the diaphragm is held on with a snap on plastic ring which is reusable with care.  I've read comments that they are inferior in some way but this may just be myth as nobody actually explained in what way they were inferior.

I like them if only because they provide an easy bit of alloy to polish.

[Lucky_Lou]

I like them if only because they provide an easy bit of alloy to polish.

Impresive photo Barry .....you can come and polish mine anytime.
Lou

[Rob Valdez 79 R65]

I've read comments that they are inferior in some way but this may just be myth as nobody actually explained in what way they were inferior.  

Only that the plastic ring will enlarge over several r/r's.  

Bing initially didn't offer the plastic ring as a replacement part - for replacing the diaphragm on a flat-top, one had to buy the complete slide assembly!

Finally, the rings became available.

We have just been talking about this in these two threads:

http://www.bmwr65.org/cgi-bin/yabb2/YaBB.pl?num=1279674119

http://www.bmwr65.org/cgi-bin/yabb2/YaBB.pl?num=1279405995

[Barry]

I agree the plastic ring issue is documented well enough on this and other forums. What I spent a long time looking for and found nothing concrete is some evidence that the flat top carbs are inferior in performance terms. Some have said they are but offer no technical explanation of why that should be.

The lack of a spring may mean the slide is more prone to stick in the bores and hang up if the clearances are not correct but that's about it and would be easily resolved.

The only other thing I can think of is that in relation to airheads in general carbs with springs had two different spring rates over the years and I've read that the stronger spring was beneficial in some respects. It may be that the piston has a tendency to oscillate in tune with the intake pulses. This is getting a bit esoteric though. In general flat tops seem to perform just fine as far as I can tell.

[BooG]

How do you get alloy looking that Bling!?!
The carbs haven't been stripped yet, but the needle pistons seem to be seized. Apparently they have not been used for a while?! There seems to be a nut missing from the enrichener shaft also. What size might that be?

[Barry]

How do you get alloy looking that Bling!?!

Flash photography tends to add to the Bling !

The 2 flat tops are the only bits of polished alloy on the bike I just use solvol autosol polish occasionally. it takes 2 mins. I'm not obsessive honest although I have also been known to buff the alloy dipstick knob as well.   8-)

That enricher nut could be a special. I measure it 11mm across flats which does make it a bit odd ball as the shaft seems to be 8mm.  If you get lucky the thread might be standard M8 (thread pitch 1.25mm) or M8 fine (thread pitch 1.0mm).

[Rob Valdez 79 R65]

Darn!  None of the microfiche descriptions gives the dimensions!

If the other carb has the nut, remove it and take it to the hardware store.

[BooG]

One of the threads off one side of the Allen screw hole that secure the flat top to the carb body is stripped. A bolt thru may solve but won't look great. Any worthwhile fixes out there? :-?

[Dizerens5]

Motorworks here sells a "choke cable clamp on carb arm pre-1980" is this what you may be looking for? Cost about $5.

[Rob Valdez 79 R65]

One of the threads off one side of the Allen screw hole that secure the flat top to the carb body is stripped. A bolt thru may solve but won't look great. Any worthwhile fixes out there? :-?

Heli-Coil or the like?

[montmil]

Might a very slightly larger SAE thread machine screw self-tap itself and remain stock looking? Might need to set up a drill press to open up the chamfered hole for the screw head a tiny bit.

I have used a modelmaker's file set to "notch" three equidistant cuts in a screw to help it believe it's actually a tap. Think fine thread aircraft hardware.

Monte