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funkamongus
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Joined: 06/25/2009
Posts: 8

Hi! Ive only posted once so far,, trying to source those nice louvered side covers Ive seen. The only other thing at this point is syncing the carbs.. I have synchronized other carbs but dont see any vacuum ports.. Can anyone clue me in??? Im thinking she runs great but theres a bit more in her.. Thank you !!!

schrader7032
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VBMWMO #7032
San Antonio, TX
Joined: 10/27/2006
Posts: 6597
New to me R75/5, carb sync'ing

I'm not sure if the early /5 carbs had vacuum ports. If they didn't, Bing sells kits and instructions on adding them. My /7 has ports that are on the outside of each carb...they might be in a different location on other carbs.

But you really don't need vacuum ports to synch the carbs. As you can imagine, this was done for years without that. Check out Snowbum's website page on the subject:

http://bmwmotorcycletech.info/synchcarbs.htm

This is a great amount of detail. But some of the basics:

- be sure the bike is warmed up
- have some spark plug extenders made. These will connect to the top of the plug and allow the cap to be attached in such a way that exposes a portion of the extender rod. This is used to short the cylinder out.
- it's important not to pull a plug wire off of a running cylinder, especially if you have an electronic ignition. It's perfectly fine to use a long plastic or wooden handle screwdrive to temporarily provide a path to ground for the spark energy.
- as an alternative to the shorting, I've heard people mention the idea of turning the mixture screw enough so as to effectively "kill" the cylinder. Then you just turn the screw back to its original position and continue with the other cylinder.
- the idle mix and idle speed is an iterative process, back and forth to get the best combination of speed and smoothness.
- the last part is ensuring that each carb cable is pulling the same amount so that each carb contributes equally to power and smoothness. The best place to do that testing is just off idle, around 1500-1700 RPM where small changes in vacuum are felt more. Once the throttle opens the butterflies up to mid range or so, it's hard to determine a difference.

Anyway, check out 'bum's article and think about the process. It's pretty straightforward, even without a vacuum port or gage.

Kurt in S.A.

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

funkamongus
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Joined: 06/25/2009
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New to me R75/5, carb sync'ing

Thank you very much for the reply!! Exactly what I was looking for..

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