13 BMW 1983 R100RS Update Pulse Air System and Replace Oil Breather Hose

The 1983 R100RS has the BMW Pulse Air system installed. This 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 low CO emissions. 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 purchased a smog kit from Rubber Chicken Racing Garage that has all the parts needed to complete this upgrade, shown below.

Pulse Air Upgrade Parts

Pulse Air System Upgrade Parts

MAX BMW has a good exploded view diagram of the Pulse Air components in their parts fiche.

Remove the Air Intake Tubes

Filtered air is sucked from the air box into the exhaust ports in the heads via the air intake tubes, one for each cylinder, where it is used to burn any unburned fuel and to reduce CO in the exhaust. The air intake tube consists two metal tubes connected with a rubber hose about mid-way along it’s length. One metal tube connects to the air box next to the carburetor inlet and the other metal tube connects to a threaded port underneath the head behind the exhaust pipe nut.

Air Intake Manifold Connection at Air Box

Pulse Air Tube Connection at Air Box That Lets Filtered Air Get Sucked Into The Exhaust Port

Air Intake Manifold Connection at Exhaust Manifold

Air Intake Manifold Connection at Exhaust Manifold

I unscrew the nut at the air box to remove that end of the air intake tube.

Air Intake Manifold Detached From Airbox

Air Intake Manifold Detached From Air Box

Then I hold onto the air valve while I remove the nut holding it to the airbox. The air valves are the two bronze color cylinders inside the air box connected together with rubber hose as shown below.

Inside Air Box Showing Air Valves (Shiny Cylinders)

Inside Air Box Showing Air Valves (Shiny Cylinders)

When the air valve senses a high vacuum in the carburetor venturi, it opens to allow filtered air to be sucked down the air intake manifolds on each carburetor into the exhaust ports.

After removing the air intake pipe connections on both sides, I lift out the two air valves and the rubber hose connecting them.

Air Valves Removed

Air Valves Removed

I remove the other end of the air intake tube from the head by unscrewing the coupling nut.

Removing Air Intake Manifold From Head

Removing Air Intake Tube From Head

This exposes a fitting in the head that I need to remove with a 22 mm socket.

22mm Fitting in Head

22 mm Fitting in Head That Lets Air Enter The Exhaust Port

Mine unscrews very easily, but they can be stuck tight due to galling, and carbon build up in the exhaust manifold.

WARNING:
Read Bob Fleischer’s write-up. 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 Fitting with 22mm Socket

Removing Fitting with 22 mm Socket

Here is the air intake tube showing the two metal pipes, the rubber hose joining them in the middle, and the plug that goes into the head.

Air Intake Manifold and Head Fitting

Air Intake Tube Parts and Head Fitting

Remove Oil Breather Hoses

The oil breather hoses are also inside the air box. One of mine has split so I am replacing both hoses. If yours are in good condition, you don’t have to touch them to upgrade the Pulse Air system as the oil breather is not part of Pulse Air system.

Split Oil Breather Hose

Split Oil Breather Hose

Top-Damaged Hose: Bottom-New Oil Breather Hoses, Right and Left Sides

Top-Damaged Hose: Bottom-New Oil Breather Hoses, Right and Left Sides

Remove Carburetor Intake Venturi Vacuum Hoses

These hoses connect from the bottom of the carburetor and go into the airbox to a tee fitting. A single hose from the tee goes to the left side air valve. The carburetor venturi vacuum opens the air valves so filtered air can be pulled by the exhaust manifold vacuum into the exhaust manifold.

Vacuum Hose on Carburetor

Vacuum Hose on Carburetor

I pull the hoses back inside the top engine cover. When I rebuild the engine, I’ll pull the air box and completely remove them.

Pulling Vacuum Hose Into Top Engine Cover

Pulling Vacuum Hose Into Top Engine Cover

Storing Hose Under Top Cover

Tucking End of the Vacuum Hose Under The Top Engine Cover

Capping Off Carburetors and Vacuum Hoses

The small screws with fiber washers fit into the threads inside the vacuum port on the carburetor. They can be removed to use carburetor balancing sticks or gauges.

Carburetor Vacuum Port Screw with Fiber Washer

Carburetor Vacuum Port Screw with Fiber Washer

Installing Screw in Carburetor Vacuum Port

Installing Screw in Carburetor Vacuum Port

Capping Off Exhaust Manifold

The oil drain plug makes a perfect cap for the threaded hole in the exhaust manifold. I snugged this up and will check it again after I ride the bike to be sure it stays put.  Due to the high heat of the head near the exhaust valve, I don’t think using Loctite would do much good as the plastic will likely become liquid.

Oil Drain Plug with Washer

Oil Drain Plug with Washer

Oil Drain Plug Installed in Head

Oil Drain Plug Installed in Head

Capping Air Intake Tube Port in The Air Box

The timing port rubber plug fits nicely into the hole in the air box where the air intake tube was connected to it. I put a bit of silicone seal the plug to ensure it doesn’t pop out. That would let unfiltered air into the carburetor and the engine.

Timing Rubber Plug Installed in Air Box

Timing Rubber Plug Installed in Air Box

Install Air Filter on Top of Air Box

I install a new air filter on top of the air box. Note that the bottom of the filter has rounded and square corners which match those on the air box so it only goes one way.

Air Filter has Different Corners to Match Air Box

Air Filter has Different Corners to Match Air Box

Filter Installed On Top of Air Box

Filter Installed On Top of Air Box

Air Box Cover Slides on Top of Air Filter

Air Box Cover Slides on Top of Air Filter

The air box cover clips come off easily. One end hooks into the bracket on the air box and is easy to install by moving the top out of the way and then holding the clip it so it’s rotated toward the inside of the air box and pushing up on the clip. When it clears the bracket, rotate it towards you.

Airbox Cover Clip

Air Box Cover Clip

Inserting Clip in Airbox Bracket

Inserting Clip in Air Box Bracket

Clip Installed in Airbox Bracket

Clip Installed in Air Box Bracket

Air Box Clip Installed

Air Box Clip Installed

Revisions

2019-11-23  Edits and typos.

13 thoughts on “13 BMW 1983 R100RS Update Pulse Air System and Replace Oil Breather Hose

  1. Thanks for a very nice article; great photos. This is one easy ‘fix’ that I’ve been thinking about. Keep up the good work in helping to support fellow airheads.

  2. Question – Do the vacuum lines from the carbs that are stuffed in the upper engine area need to be capped off?

    Thanks for all the information

    • Hi Jay,

      They go nowhere so putting them inside the engine cover is okay, or they can be removed if you wish.

      I hope this helps.

      Best.
      Brook.

  3. For anyone doing this to an R65, use M16x1.5 bolts for the exhaust manifold capping. The oil drain plug (M18x1.5) is too large. Speaking from experience.

    Thanks again for this post, Brooks!

  4. Thanks, Brook! You, Snowbum and Tom Cutter sure save us amateur airheads a lot of headscratching, blind alleys and breaking stuff. I’ll get Tom’s kit and desmog my R80 RT.

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