- Install Air Box
- Install Carburetor Cables
- Install Carburetors And Air Horns
- What Done Looks Like
When I got the bike, it had no carburetors. I show how I remove the airbox in this write-up.
I found a useable set of used carburetors and I rebuilt the carburetors as shown here.
Since I replaced the right side handlebar controls, I have to replace the throttle cam that fits inside the throttle housing since the cam design changed in later years so it has a larger hole in the center.
|07 12 9 952 121||HOSE CLAMP – L=47-54MM||6|
|13 72 1 254 654||RUBBER GROMMET – D=52MM||2|
|07 12 9 952 123||HOSE CLAMP – L=53-60MM (from 09/78)||4|
|13 72 1 264 392||RUBBER GROMMET – D=60MM||2|
|13 72 1 337 229||PIPE, Airbox||2|
|13 72 1 337 162||RUBBER VALVE, Air Box||1|
|13 72 9 062 492||AIR FILTER ELEMENT, Mahle||1|
|13 72 1 337 342||HOSE CLAMP – SLS, Airbox Rebreather Hoses||2|
|13 72 1 337 511||VENT HOSE, LEFT, Airbox Rebreather||1|
|13 72 1 337 512||VENT HOSE, RIGHT, Airbox Rebreather||1|
|13 72 1 337 105||BOW,Airbox Cover||4|
|32 73 1 242 014||CABLE ADJUSTER||2|
|32 73 2 301 342||PROTECTION CAP, Cable Adjuster||2|
|32 73 1 242 125||ACCELERATOR BOWDEN CABLE – L=770MM, Handlebar||1|
|32 73 1 242 132||ACCELERATOR BOWDEN CABLE – L=487MM, Carburetor Right||1|
|32 73 2 302 232||ACCELERATOR BOWDEN CABLE – L=382MM, Carburetor Left||1|
|32 73 1 242 594||CHOKE CABLE – L=764MM, Handlebar||1|
|32 73 1 242 138||CHOKE CABLE, BOTTOM – L=487MM, Carburetor||2|
|32 72 1 457 080||CAM DISC – L=33MM (from 09/80)||1|
VIDEO: 1983 BMW R80ST Install Carburetors, Cables, Airbox
Install Air Box
I remove the pulse air system so I don’t install those components. I did a similar modification for the 1983 R100RS rebuild and I will borrow some of the content from that document in this one, as appropriate.
I previously installed the air box itself when I installed the transmission. You can see how I do that here.
Install Rubber Fittings
I use a kit supplied by Tom Cutter at Rubber Chicken Racing Garage to update the airbox when it isn’t using the pulse air system components. There are two timing hole rubber plugs that seal off the air lines that went to the exhaust valve pipes that I insert into the holes on the sides of the airbox.
I previously installed the rubber air valve on the rear of the air box when I mounted it during the transmission install. I install the rubber grommet that the tee fitting for the carburetor vacuum lines fit into, but I don’t install the plastic tee fitting. Instead, I put some silicone seal into the hole in the grommet to prevent unfiltered are from being pulled into the air box.
Install Air Horns Inside Airbox
I show how I do this in the 1983 R100RS document. Here is the link.
Here are some pictures from the 1983 R80ST.
Install Air Filter And Top Cover
I show how I do this in the 1983 R100RS document. Here is the link. On the 1983 R80ST, I don’t have coils interfering with installation of the top cover.
Here are some pictures from the 1983 R80ST.
Install Carburetor Cables
The 1983 R80ST has a single throttle and choke cable at the handlebar that attaches to a Bowden housing. The throttle and choke cables that come from the carburetors attach to the other side of the housing. Earlier model bikes have two throttle cables at the handlebar, each going to a carburetor, and a lever on the left side of the clam shell air filter box that actuates the chokes.
On the 1983 R80ST, the right side of the frame spine is consumed with electrical components, so both the throttle and choke cables from the handlebar route to the left side of the frame spine.
Assemble Bowden Connectors
The throttle cables and the choke cables use a separate Bowden connector. The Bowden connector has a plug inside that the three carburetor cables connect to. The two cables that go to the carburetors come through the screw-on cap and fit into the wide slots on the sides. The cable from the handlebar comes into the other end of the connector housing and slips through the narrow slot in the side of the plug. There is a rubber cover the fits over the end of the handlebar cable with the adjuster screw and lock nut. I remove the lock nut from the threaded cable adjuster. I use some Ruglide tire mounting spray to make it easier to push the cover over the screw threads and the end of the adjuster. Then I install the handlebar cable into the narrow slot and then put the plug inside the Bowden connector housing and screw on the cover with the two carburetor cables.
Install Choke Cables And Adjust Choke
The two choke cables from the Bowden connector to the carburetors are the same length. I install the carburetor choke cables into the carburetor by putting the round cylinder on the end of the cable into the hole on the choke lever arm and then screws in the cable adjuster all the way into the top of the carburetor. I adjust the handlebar cable adjuster on the Bowden housing until the choke lever touches the bottom pin when the choke is off for both carburetors. I use the carburetor cable adjuster on each carburetor to get the choke lever to touch the top pin when the handlebar choke lever is in the full on position on both carburetors. When have the chokes on both carburetors working correctly I tighten the lock nuts on the carburetor choke adjusters.
I place the carburetors on top of the cylinders while I adjust the cables so it’s easy to work on them.
Install Throttle Cables And Adjust Carburetors
The R80ST throttle cables are different lengths. The left side carburetor uses the shorter cable since it’s closer to the Bowden connector than the right side carburetor. I need to set the throttle stop screw and idle screws to initial static settings that will let me start the engine. Later I’ll dynamically just the carburetors while the motor is running to get the carburetors balanced and to ensure both throttle plates are opening at the same time.
I use a piece of paper to adjust both throttle stop screws so they are just contacting the throttle arm. I slide the paper between the face of the screw and the contact tab on the throttle arm. I adjust the stop screw until it is tight enough that I can’t easily extract the paper. This ensures both carburetor butterfly plates will be in just about the same position. Then I turn the throttle stop screw one full turn inward which should let me start the engine.
I screw in the idle mixture screw gently until it’s just seated. Then I back out the screw 3/4 of a turn which should let me start the engine at the first engine start and keep it idling.
I route both the choke and throttle cables on the left side of the frame spine tube. I’ll use some cable ties to secure the Bowden connectors to the frame later.
Install Carburetors And Air Horns
Some of the pictures in this section are taken from the 1983 R100RS rebuild.
The outlet side (end with the throttle plate visible) of the carburetor mounts on the intake port of the head into a rubber bushing secured with two large hose clamps. The intake side (end with the slide visible) mounts to the air box using a plastic air horn that has a large rubber sleeve on the air box end of the air horn and is secured with three large hose clamps; two on the air box aluminum sleeve in the air box air horn and one on the carburetor. The 1983 R80ST air horns are the same length.
The MAX parts fiche shows the same size hose clamps (part# 07 12 9 952 121; 47-54 mm) for all fittings on the carburetors. This is in error. The two hose clamps for each carburetor that secure the rubber sleeve onto the aluminum spigot of the air box have to be bigger and are part# 07 12 9 952 123; 53-60mm.
I slide the rubber bushing over the intake spigot and put two hose clamps over it, but I leave them loose for now. Then I push the carburetor into the sleeve.
The carburetor air horn has a rubber sleeve that goes over the aluminum sleeve inside the air box air horn. I push the sleeve down the carburetor air horn until it’s flush with the end of the tube. I put the smaller hose clamp on the other end and push it over the intake side of the carburetor. I put the two larger hose clamps on the end with the rubber sleeve.
I align the carburetor air horn with the aluminum sleeve and push the rubber sleeve on the carburetor air horn over the aluminum sleeve in the air box. I orient the rubber sleeve so it’s flush with the side of the air box and then tighten the two hose clamps. Then I tighten the hose clamp on the carburetor intake and then the two clamps on the rubber sleeve on the intake spigot in the head.
What Done Looks Like
Here’s how it looks with the airbox, carburetors and cables installed.