13 BMW 1983 R80ST Remove Air Box & Pulse Air System

The air box is secured to the top of the transmission. Inside are components for the crankcase rebreather system and for the Pulse Air System which is a passive system designed to reduce emissions to meet the US standards in the early to mid-1980’s.

Air Box With Pulse Air And Crankcase Rebreather Components-And Some Leaves

Air Box With Pulse Air And Crankcase Rebreather Components-And Some Leaves

NOTE:
The picture was taken when I first saw the bike and the air box cover was missing. Leaves are not part of the crankcase rebreather or pulse air system inside the air box. 🙂

I don’t show how to remove the carburetors and air box cover as mine were already off the bike with I got it. But you can see all the details from the 1983 R100RS project.

Pulse Air System Description

The Pulse Air System is a passive system with no active motors or moving parts. It sucks filtered air into the exhaust manifold in the heads to help burn any gasoline and to ensure CO emissions are converted to CO2. That said, according to Bob Fleischer’s information on the Pulse Air system, this increases the exhaust gas temperature and likely exacerbates wear of the valves and seats and could contribute to warped heads. The original valves and seats in 1983 had problems with valve recession due to excessive wear from the metallurgy BMW used to try and compensate for unleaded fuel.

For these reasons, I’m going to update the Pulse Air system and modify the air box so the valve train stays nice and cool. I will purchase a smog kit from Rubber Chicken Racing Garage that has all the parts needed to complete this upgrade.

Video

Here is a short video summarizing how I remove the air box and the Pulse Air System.

VIDEO: 1983 BMW R80ST Remove Air Box & Pulse Air System

Remove Crankcase Rebreather Components

On bikes with the rectangular air box on top of the transmission, the crankcase rebreather routes gases from the crankcase to both carburetors. The earlier version used with the aluminum clam shell housing for the air cleaner routed all the vapor to the right carburetor. The rebreather hose from the rebreather valve under the top engine cover enters the air box and has a plastic tee that connects to hoses that go to the left and right air horns the carburetor intake attaches to.

Crankcase Rebreather Hose Attaches To Plastic Tee With Wire Clip

Crankcase Rebreather Hose Attaches To Plastic Tee With Wire Clip

The hoses are secured to the plastic tee with wire clips. I remove the clips and pull the hoses off the tee.

Crankcase Rebreather Hose Clip Detail

Crankcase Rebreather Hose Clip Detail

The other end of the rebreather hose connects to the side of the air horn and is attached to a plastic pipe that sits in the center of the air horn.

Crankcase Rebreather Hose Attaches To Side Of Air Horn

Crankcase Rebreather Hose Attaches To Side Of Air Horn

Crankcase Rebreather Pipe Centered In Airhorn That The Rebreather Hose Attaches To

Crankcase Rebreather Pipe Centered In Airhorn That The Rebreather Hose Attaches To

I pull the hose out of the air horn with the plastic pipe attached and then carefully remove the plastic pipe from the hose. I pull the plastic pipe out from the outside of the air horn as it has three fragile plastic legs that center the pipe inside the air horn and I don’t want to break them.

Pulling Crankcase Rebreather Hose And Plastic Distribution Pipe Out Of Air Horn To Remove It From Plastic Pipe

Pulling Crankcase Rebreather Hose And Plastic Distribution Pipe Out Of Air Horn To Remove It From Plastic Pipe

Crankcase Rebreather Plastic Pipe Is Centered Inside Air Horn By Three Fragile Plastic Legs

Crankcase Rebreather Plastic Pipe Is Centered Inside Air Horn By Three Fragile Plastic Legs

Crankcase Rebreather Hose Attaches To Plastic Pipe

Crankcase Rebreather Hose Attaches To Plastic Pipe

Now I remove the metal sleeve in the side of the air box that the carburetor intake pipe attaches to. It also secures the air horn in the hole on the side of the air box. Then I push the rubber air horn into the inside of the air box to remove it.

Metal Sleeve Secures Air Horn To Air Box And Attaches To Carburetor Intake Tube

Metal Sleeve Secures Air Horn To Air Box And Attaches To Carburetor Intake Tube

Air Box Carburetor Airhorn Removed

Air Box Carburetor Airhorn Removed

Air Box Carburetor Air Horn With Crankcase Rebreather Hose And Fittings

Air Box Carburetor Air Horn With Crankcase Rebreather Hose And Fittings

Remove Pulse Air System Components

The pulse air system has a metal pipe that exits the air box. There is a rubber section in the middle and then another metal pipe that attaches to a fitting underneath the exhaust port in the cylinder head. The pipe supplies air to the exhaust port to burn any unburned fuel and to ensure any CO is converted to CO2. I remove this pipe from the air box. It is secured with a nut on the end of the metal pipe.

NOTE:
You will see leaves inside the airbox that were on the bottom of the box under the components. The bike was outside without the air box cover when I got it. Needless to say, these are not part of the internal air box components. 🙂

Pulse Air Line From Air Valve Attaches To Fitting On Side Of Air Box

Pulse Air Line From Air Valve Attaches To Fitting On Side Of Air Box

Removing Pulse Air Line From Air Box

Removing Pulse Air Line From Air Box

Pulse Air Line Fitting Hardware Detail

Pulse Air Line Fitting Hardware Detail

Then I remove the retaining nut that secures the pulse air valve to the side of the airbox. I pull the rubber vacuum hose off the nipple on the top of the pulse air valve. Then I remove the wire clip and remove the air hose from the pulse air valve so I can remove the valve from the air box.

Remove Nut Securing Pulse Air Valve To Air Box

Remove Nut Securing Pulse Air Valve To Air Box

Pulse Air Valve Vacuum Line

Pulse Air Valve Vacuum Line

Pulse Air Valve Vacuum Line Pulls Off Nipple At Top Of Valve

Pulse Air Valve Vacuum Line Pulls Off Nipple At Top Of Valve

Clip On Air Hose To Left Pulse Air Valve

Clip On Air Hose To Left Pulse Air Valve

Left Pulse Air Valve Removed

Left Pulse Air Valve Removed

Left Pulse Air Valve Hardware Detail

Left Pulse Air Valve Hardware Detail

Then I remove the right side pulse air valve in the same way. The left and right pulse air valves are different and the right valve does not have the vacuum line nipple. The left valve opens using the carburetor vacuum and sends air to the right valve via the large rubber hose.

Pulse Air Valves and Hardware Detail

Pulse Air Valves and Hardware Detail

Next I finish removing the air pipe from the fitting underneath the exhaust port and the fitting from the cylinder head. The fitting in the cylinder head can be hard to remove, but mine came out easily.

WARNING:
Read Bob Fleischer’s write-up in the “Pulse Air Description” section above. This fitting often won’t budge and you can damage the aluminum threads in the head if it’s really stuck. Follow Bob’s other ways of upgrading the Pulse Air system if your fitting won’t come out easily.

Removing Pulse Air Line From Cylinder Head Fitting

Removing Pulse Air Line From Cylinder Head Fitting

Cylinder Head Pulse Air Fitting

Cylinder Head Pulse Air Fitting

Removing Cylinder Head Pulse Air Fitting With 22 mm Socket

Removing Cylinder Head Pulse Air Fitting With 22 mm Socket

Cylinder Head Pulse Air Fitting Hardware Detail

Cylinder Head Pulse Air Fitting Hardware Detail

Pulse Air System Air Line With Rubber Hose Section In The Middle

Pulse Air System Air Line With Rubber Hose Section In The Middle

Remove Air Box

Now all the components inside the air box are removed, I can access the air box mounting hardware. The top left bolt and top right nut inside the air box secure it to the transmission and also secure the transmission to the engine block. There are two bottom bolts on the transmission that secure it to the engine block as well. The middle bolt inside the air box only secures the box to the transmission.

Bolts *Left and Middle) And Nut (Right) That Secure Air Box To Top Of Transmission

Bolts *Left and Middle) And Nut (Right) That Secure Air Box To Top Of Transmission

Before I remove the bolts and nut, I remove the crankcase rebreather plastic tee and then push the rebreather rubber grommet back through the air box with a screwdriver.

Pulling Rebreather Hose Tee Out Of The Rebreather Hose

Pulling Rebreather Hose Tee Out Of The Rebreather Hose

I remove the bolts and nuts. Each has a thick flat washer. I use a wrench on the left bolt, a box end ratchet on the right nut and a socket on the center bolt.

Removing Air Box/Transmission Left Bolt

Removing Air Box/Transmission Left Bolt

Air Box/Transmission Left Bolt & Thick Washer

Air Box/Transmission Left Bolt & Thick Washer

Removing Air Box/Transmission Right Nut

Removing Air Box/Transmission Right Nut

Air Box/Transmission Right Nut & Thick Washer

Air Box/Transmission Right Nut & Thick Washer

Removing Air Box Center Bolt

Removing Air Box Center Bolt

Air Box Center Bolt & Thick Washer

Air Box Center Bolt & Thick Washer

I pull the vacuum hose off the nipple. The two hoses that go to the carburetors are connected to the nipple tee on the back of the air box. After I remove the air box off the transmission I remove the hoses from the tee, push it into the air box and then use a screw drive the push the grommet out of the air box.

Pulse Air Valve Vacuum Hose Pulls Off Nipple Of Tee

Pulse Air Valve Vacuum Hose Pulls Off Nipple Of Tee

Carburetor Vacuum Lines With Tee Entering Back Of Air Box

Carburetor Vacuum Lines With Tee Entering Back Of Air Box

Pulse Air Valve Vacuum Tee, Grommet & Carburetor Hoses

Pulse Air Valve Vacuum Tee, Grommet & Carburetor Hoses

Here is the crankcase rebreather rubber hose that comes from the rebreather valve underneath the top engine cover. You can see the rebreather housing that is the rectangular box on the right side of the top engine cover

Crankcase Rebreather Hose-Rebreather Valve Housing On Right Under Top Engine Cover

Crankcase Rebreather Hose-Rebreather Valve Housing On Right Under Top Engine Cover

You can see where the air box mounting bolts and the nut fit on the transmission.

Top Of Transmission With Air Box Removed

Top Of Transmission With Air Box Removed

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