This “project bike” came with it’s original gas tank. There was a small dent in the tank near the front and scraps and gashes in the paint. The inside red tank lining was in good condition. I refurbished the gas cap, put on new BMW roundels, replaced the rear bracket that secures the tank to the spine tube and installed new fuel lines.

Here are some before and after pictures of the gas tank.

Parts

I got all the parts from Euro MotoElectrics who graciously provided parts for this project at no cost.

Part #	Description	Qty
16 12 1 233 557	FUEL COCK KARCOMA R26-/5/6/7	1
16 12 1 233 368	STRAINER	1
46 63 7 686 746	BADGE – D=70MM, Includes Rear Fender Decal	3
16 11 1 240 159	HOLDER. Tank Latch	1
16 11 1 237 553	SUPPORT RIGHT	1
16 11 1 237 552	SUPPORT LEFT	1
51 25 1 453 148	GASKET, Gas Cap	1
13 11 1 254 083	DISTRIBUTION PIECE, Fuel Hose Fitting	1
16 11 2 307 360	RING, Gas Cap	1
16 13 2 307 010	HOSE – 1330MM	1
13 11 1 338 115	BULK MATERIAL, FUEL HOSE – 6X11 (meter)	1

Video

This is a video showing a summary of how I do this work.

VIDEO: 1983 BMW R80ST Assemble & Install Gas Tank

Refurbish Gas Cap

There is a rain cover and rubber gasket on the gas cap. I replaced them. I used a screwdriver to pry the rain cover over the top of the gas gap. I removed the rubber gasket that fits between the bottom of the cap and the top of the tank by rolling it down the threads of the gas cap. I installed the new rain cover from the top of the gas cap pushing it down with my fingers as far as I could. Then I used a small blade screwdriver to carefully lever the edge of the rain cover over the top edge of the gas cap.

Mount Gas Tank

The gas tank mounts on a rubber bumper on the front of the frame. There are two “L” shaped rubber bumpers that fit over the rear frame tubes between the gas tank and the frame. The left and right rear bumpers are different. The bumpers have a thick leg and a thin leg. The thick leg goes between the bottom of the gas tank and the top of the frame tube and the thin leg goes between the side of the gas tank and the side of the frame tube.

There is a bracket with rubber tube on the rear of the gas tank. It fits over the end of the spine tube. I replaced it with a new one. I used some pliers to pull apart the legs of the bracket so I can remove it from the bracket is slides into on the bottom of the gas tank. Then I pried apart the legs of the new bracket and inserted through the bracket on the bottom of the tank and then used the pliers to squeeze the legs closed again.

NOTE:
The thick leg of the rear rubber bumper was a bit too thick to allow the rear bracket to easily fit over the spine tube. So I used a razor blade the remove some of the rubber from the thick part of the legs.

Install BMW Roundel

After I mounted the tank, I applied the BMW roundels to each side of the gas tank. I remove the paper backing from the sticky side of the roundel. I carefully hold it above the cutout on the gas tank for the roundel and carefully centered it in the cutout and then pressed it down.

Install Petcock & New Fuel Lines

The R80ST gas tank has only one petcock. I install the new petcock on the threaded fitting on the left side of the gas tank. The petcock has a fiber washer that fits between the gas tank fitting and the bottom of the petcock nut.

I loosened the airbox mounting hardware so I can tilt it up to allow me to push the new fuel line through the cutouts in the front of the airbox and underneath the airbox.

I start on the right side. I insert the fuel line all the way onto the right carburetor spigot. Then I push the rest of the line through the right-side hole between the airbox and engine housing and pull it through on the left side. I leave some slack in the fuel line going to the right carburetor.

I use the new tee fitting and place on the left end of the fuel line so the top leg of the tee is close to the petcock spigot and the bottom leg is close to the left carburetor spigot. I make a mark in the fuel line so it will fit all the way to the shoulder on the horizontal leg of the tee and cut the fuel line with a razor blade and insert it onto the horizontal leg of the tee.

Then I attach the end of the fuel line onto the plastic spigot of the petcock and again make a mark on the fuel line next to the shoulder of the vertical leg of the tee. I leave some slack in the fuel line so it will fit between the throttle and choke cables of the left carburetor.

Then I attach the fuel line all the way onto the left carburetor spigot and measure it so it fits up against the shoulder on the lower leg of the tee.

Then I remove the gas tank and install the overflow line onto the spigot in the middle of the left side of the gas tank and reinstall the gas tank and fuel line onto the petcock. I route the overflow hose over to the right side of the bike at the rear of the gas tank and route it down near the rear brake master cylinder so if any fuel comes out it won’t end up on the exhaust pipes.

Here is what done looks like.