Greetings,
The bike in question is a 1986 R65, which I recently acquired. Strangely, it has a hose connecting the vacuum ports (the ones with the screw where you would mount a carb balancer) - presumably the work of the PO (who is no longer around to ask). My general intuition is to remove it and put new screws in where they're supposed to be. But, just to make sure, this isn't something that BMW did, is it?
I kind of see where someone might have thought this was a good idea, but I don't think it actually does what they thought it did, since the vacuum on the two carbs doesn't take place at the same time. So rather than some kind of balancer, all it is is a vacuum leak in both carbs (and not even an equal one, if they aren't already balanced).
Or, am I all wrong and this is an innovation that took place in 1986, only to be discarded on my later 1988 R100RS? Or a stroke of brilliance by the PO? Any insight?
Just for reference, the engine runs very smoothly, but maybe that's pure coincidence.
On your bike, that hose was part of the air injection system or secondary air injection system, BMW installed around 81 or so. It tied into a bunch of plumbing in the air filter housing.
Take a look at Max BMW's microfiche for a better idea of what was involved.
If the hose just connects the two carbs, it has been modified by the previous owner. St.
Beware! I do not suffer fools gladly! St.
Thank you Steven, very interesting. I had assumed it was the PO but it looked slightly "official", which is why I asked. I had looked at the fiche, and it showed the screw for that model, but I didn't think to dig deeper. I'll know more when I take it all apart. I appreciate your valuable insight.
Looking further, thanks to your clues, I see it on the fiche as a California modification, and I found an article on it (called the "Pulse Air" system) on Snobum's site.
Again, thank you for pointing me in the right direction.
Scott
Lots of dual carb bikes use a balance tube. I had a late 80's R100 with that tube on it and it didn't seem to hurt or help. I left mine in-place mainly because I was too busy repairing other bits to buy the 2 screws. In my mind it's a non-issue.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Max BMW's microfiche shows a diagram of the secondary air injection system that most likely would be on your bike from the factory. At least for USA and California models. European bikes most likely didn't have this system.
I am surprised you don't have this system on your RS? My limited understanding is that newer bikes had even more "plumbing" to meet air standards.
Regardless, the balance tube between the carbs is not a bad thing, but doesn't do much in the grand scheme of things. As long as the hose is in good condition and not leaking, save the money on the screws, LOL, BMW probably wants an arm and leg for them. St.
Beware! I do not suffer fools gladly! St.
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