Balancing slide carburettors

[JohnT]

On Bing slide carbs there is no Vacuum take off point to enable balancing and no convenient point to drill, tap and fit a take off point.
On the air cleaner side there is.
would a meaningful vacuum be available on that side?

[SteveD]

Driling, and using a manometer is the most precise way to sync carbs on the old bing units. But if you don't want to drill, this is a way do it , and it will be close enough. First make shure the valve clearence is correct, remove the air intake tubes, back the idle speed screws out so that the slides bottom, make shure you have alittle play in the cables, about 1mm, or .040, put your finger on one slide and watch the other while slightly turning the throttle, you will be able to see or feel if one slde moves before the other, adjust the cables acordingly. Start the engine and let it warm alittle, set the idle speed, then check the slides again too make shure they are lifting evenly. I have used this method for years. On many old multi cyclinder motorcycles this is the only way it could be done.

https://forums.bmwmoa.org/threads/bing- ... ort.30592/

[JohnT]

Yes that's how I used to set Triumph Bonneville carbs many years ago.
Am shortly taking on a running R50/5 project that has Chinese carbs fitted at present but would like to reinstate the correct slide type Bings and hopefully find space on the body to add a vacuum take off port. Time will tell.

[Rob Frankham]

Driling, and using a manometer is the most precise way to sync carbs on the old bing units. But if you don't want to drill, this is a way do it , and it will be close enough. First make shure the valve clearence is correct, remove the air intake tubes, back the idle speed screws out so that the slides bottom, make shure you have alittle play in the cables, about 1mm, or .040, put your finger on one slide and watch the other while slightly turning the throttle, you will be able to see or feel if one slde moves before the other, adjust the cables acordingly. Start the engine and let it warm alittle, set the idle speed, then check the slides again too make shure they are lifting evenly. I have used this method for years. On many old multi cyclinder motorcycles this is the only way it could be done.

https://forums.bmwmoa.org/threads/bing- ... ort.30592/

That's the old time way of doing it and is probably sufficient. A sensible variation is to use a rod of given thickness... a twist drill is ideal... to set a preliminary idle setting then adjust from there.

If you want to get a bit more 'scientific' then there are a couple of other options...

1) Gunson used to do a kit which had an adjustanble shutter to fit over the inlet of the carb. You would set up the shutter and adjust on carb with the engine just off idle then move the shutter to the other carb before adjusting it to match. Could be made to work but I'm not convinced that it was much more accurate than the 'throttle slide lift' method.

2) My R60/6 (original carbs) has the head side flangs of both drilled for a take off. This allows a normal pair of manometers or gauges to be used. The benefit of doing both carbs at the same time is that, then, you can be sure that the same variables apply to both.

Rob

[JohnT]

Hi Rob.
Point 2) you say flanges are drilled. Aren't your carbs clip mounted like R50/5?
Do you have a photograph?

[Rob Frankham]

Hi Rob.
Point 2) you say flanges are drilled. Aren't your carbs clip mounted like R50/5?
Do you have a photograph?

Apologies, my post was misleading. It's the heads that have been drilled and threaded (not by me but by a PO) Normally the resultant holes are blocked with a screw. I've had to make a pair of adaptors to connect vacuum gauges. Will try to get a photo later.

Rob

[Rob Frankham]

Image of the balance ports drilled in the underside of the ports on the head... 6mm tapped hole, the outside of the hole is face flat and the 6mm allen screw has a copper washer.Probablw wouldn't have done it myself but it works fine...

Rob

[JohnT]

Thanks Rob and a nice unobtrusive mod.
I now have the bike complete with Chinese Dellorto slide carbs. I was hoping to re fit the Bings but there condition is amazingly bad.
Severe corrosion and erosion of the aluminium, one float bowel rotted through from the outside!
Will persevere with the fake Dellorto's which require some jet changes to improve running and will drill and tap the carb. bodies close to the head connection to give a vacuum take off point.