Grey/brown vacuum lines on 83 R80

[bearsfolks]

Looking through my Clymer manual and looking at the bike, I see two small tubes exiting the airbox, but just hanging beside the engine. From what I have read, these are vacuum lines that attach to the carburetors somewhere? I can't see where. The link about removing the air injectors that everyone refers to is currently down, so I can't see the photos . I have removed the air injector lines and used ball bearing to close the connections. Where do these vacuum lines connect to the carbs? Thanks

[PGlaves]

There should be a short stub pipe sticking down on the bottom of each carburetor. Same place you would attach Carb Stix or other manometer to synch the carbs. If the hoses are off the take-off ports (stubs) need to be capped or plugged.

[20774]

I'm not aware of any vacuum lines that connect to the carbs, not on a stock bike, for running conditions. Maybe for dealing with balancing, as Paul suggests. What's the other terminus of these lines?

I'm guessing it's some kind of PO mod. I don't think that the '83 models had any fuel control valve that is supposed to shut off fuel to the carbs when the ignition is off.

I'm thinking you're referring to plastic/rubber lines....maybe you mean steel tubes.
The steel tubes would be part of the pulse air system, one end goes to the airbox, the other end goes to the head. Is this the webpage that you were referring to:

http://bmwmotorcycletech.info/pulseair.htm

[PGlaves]

I'm not aware of any vacuum lines that connect to the carbs, not on a stock bike, for running conditions. Maybe for dealing with balancing, as Paul suggests. What's the other terminus of these lines?

I'm guessing it's some kind of PO mod. I don't think that the '83 models had any fuel control valve that is supposed to shut off fuel to the carbs when the ignition is off.

I'm thinking you're referring to plastic/rubber lines....maybe you mean steel tubes.
The steel tubes would be part of the pulse air system, one end goes to the airbox, the other end goes to the head. Is this the webpage that you were referring to:

http://bmwmotorcycletech.info/pulseair.htm

The lines - in stock configuration - go from the take of ports on the carbs to air valves inside the air box, which are part of the air tube system that routes filtered air to the exhaust ports. Those part metal/part rubber lines that connect on the bottom of the heads. If you take off the air filter the valves are visible inside the air box.

[flash412]

PGlaves is exactly right. When the cylinder is on the intake stroke, those small lines provide a pulse to the fart-sucker device inside the airbox (one per cylinder). Said pulse moves a diaphragm. On the other side of the diaphragm, a pulse of fresh air is sent via the metal (then rubber, then metal) tube to be injected into the exhaust flow as it exits the head. The intent is that the pulse of fresh air allows any HOT unburned hydrocarbons a second chance to combust, lowering emissions.

A pair of rubber flywheel plugs fill the holes in the airbox nicely, held with some epoxy. A 3/8" x 16 tpi flat head cap screw will fill the fittings that are in the heads quite nicely after you remove and tap them for said bolt. I forget what metric screw fits the carb ****. But again, a flat head screw of the right thread will screw in quite nicely and plug those holes, too.

[20774]

I've never been around these systems, so I was not aware of some of the connections. I was familiar with the hard lines that plug into the heads. After reading Haynes, it says the rubber lines to the carbs are to use the vacuum created in the carbs to shut off the air supply to the exhaust ports when the throttle is closed under deceleration. I think this was supposed to help with the popping sounds...

[bearsfolks]

I found the nipple where the vacuum hoses attach to the carbs, right where you fine people said they:wave would be. The carbs were overhauled about a year ago, and it appears the shop never reconnected the vacuum lines. This should improve the rough idle. Thanks again.

[PGlaves]

I found the nipple where the vacuum hoses attach to the carbs, right where you fine people said they:wave would be. The carbs were overhauled about a year ago, and it appears the shop never reconnected the vacuum lines. This should improve the rough idle. Thanks again.

Now that you don't have a vacuum leak it would be a good idea to reset the idle mixture using the idle mixture screws. Or have the shop or other experienced tuner do it.