This bike came without any carburetors. I found a set of used 32 mm BING carburetors (64/32/323-324) after searching through a box of used carburetor’s in one of Clem Cykowski’s storage rooms that I can use . The date stamps on them indicate the 323 was manufactured in 11/1982 and the 324 was manufactured in 10/1982.
The BING manual indicates the set of used carburetors I got were used on the R80 engine. But I learned from Bud Provin that the 1978 R100/7T also used this carburetor model. The BING manual does not show the R100 used this model. Oh well, with that many changes in R80 carburetors it’s likely BING doesn’t show them all in their manual.
According to the MAX BMW parts fiche, the R80ST originally had the 64/32/351-352 model carburetors. However, MAX lists two other models that can be used with the R80ST. Parts fiche typically list what is still in stock and will work, not necessarily what was originally used. Tom Cutter at Rubber Chicken Racing Garage told me that the 351-352 carburetor model was the original carburetor used on the two year production run (1983-1984 model years) of the R80ST. He also mentioned that the first 12 R80ST used the same carburetors installed on the R80 G/S.
- 64/32/351-352 (to 10/1984)
- 64/32/321-322 (to 03/1985)
- 64/32/357-358 (from 11/1984)
According the the BING carburetor manual, these are the jets used in these carburetors.
|Model||Slide||Main Jet||Need. Jet||Jet Need.||Atomizer||Idle Jet|
The BMW part numbers for the jet needles are:
BING # BMW Part #
251 13 11 1 337 692
241 13 11 1 255 840
The BING manual shows 7 different carburetor models used on bikes with the R80 engine. That’s a lot of changes. I learned from Bob Fleischer that BMW made a lot of carburetor changes in the 1980’s, particularly with the R80 engine. They were trying to meet emissions requirements and to correct reports of low mileage for the R80 engines. So that explains the large number of BING manual entries.
Based on input from Lloyd Provin, and the fact all the MAX identified carburetors used with the R80ST engine had “45” idle jets, and the fact BMW was trying to lean out the motors to meet emission standards, I’m going to use a “45” idle jet when I rebuild the carburetors. I’ll use the same main jet (150), needle jet (2.66) and jet needle (241) that the 323-324 carbs came with. Then as I do my shake down riding of 1,000 miles or so, I’ll adjust the carburetor jetting if required.
Bob Fleisher provides a link about two service bulletins BMW published regarding changes to the R80ST carburetors and the low fuel mileage situation.
There was a change made in August 1984 to the top of the air box so that the two snorkels are different lengths (part# 13 72 1 337 675). I’ll consider this modification if I have issues with low fuel mileage, but for now, I plan to use the original cover with equal length snorkels (part# 13 72 1 337 228).
Reuse Of 1983 R100RS Documentation
These 32 mm carburetors are very similar to the 40 mm carburetors used on my 1983 R100RS rebuild, and both are constant velocity carburetors. So I will reuse that documentation as appropriate. The 64/32/321-322 carburetors I’m using on the R80ST use the handlebar chock lever as is the case with the 94/40/114-113 used on the 1983 R100RS. So the details of the carburetors are the same with the exception that the 1983 R80ST carburetors I am using are 32 mm instead of the 40 mm ones used on the 1983 R100RS.
Here is a link to the theory of operation of the Bing Constant Velocity type of carburetor:
Bob Fleischer has a lot of information about various types of Bing carburetors on his web site:
- Bing CV Carburetors and Overhaul-Part 1 of 2 Parts
- Bing CV Carburetors, Part 2-Notes, Tuning … and Overhaul Items
The exploded view diagrams for these two types are the same as shown below, even though some of the parts are different on the two types.
I bought more parts than are required to rebuild the carburetors since parts were missing and damaged on these carburetors. Below is the carburetor rebuild parts list and the missing-damaged parts list. All were contributed by Euro Motoelectrics in support of my goal to auction the bike and donate all proceeds to the Motorcycle Relief Project.
Carburetor Rebuild Parts
|13 11 1 258 051||SET: GASKET SET CARBURETTOR||1|
|13 11 1 255 840||NOZZLE NEEDLE (to 05/83), Jet Needle||2|
|13 11 1 261 702||JET – 2,66, Needle Jet||2|
|13 11 1 254 766||FLOAT||2|
|13 11 1 254 768||PIN, Float||2|
|13 11 1 254 738||CSK.FILLISTER HEAD SREW, Throttle Plate||4|
|13 11 1 260 972||MAIN JET – 150 (to 05/83)||2|
Missing-Damaged Carburetor Parts
|13 11 1 335 600||VENTURI, Main & Needle Jet Holder||1|
|13 11 1 254 760||NUT||4|
|13 11 1 254 759||WAVE WASHER||2|
|13 11 1 337 368||LEVER, Choke||1|
|13 11 1 337 369||LEVER, Choke||1|
|13 11 1 336 924||IDLING JET – 45 (from 05/83)||2|
|13 11 1 335 302||IDLING MIXTURE SCREW||2|
|13 11 1 254 736||SPRING, Idle Mixture||2|
|13 11 1 260 973||PRE-ATOMIZER||1|
|13 11 1 254 732||WASHER||2|
|13 11 1 337 359||FILLISTER-HEAD SCREW, Slide Ring||8|
|13 11 1 335 306||SPRING WASHER, Slide Ring, Throttle Bracket||12|
|13 11 1 335 606||TENSION SPRING, Throttle Return||2|
|13 11 1 259 869||FILLISTER HEAD SCREW, Vacuum Port||2|
|13 11 1 259 870||GASKET RING, Vacuum Port||2|
|13 11 1 337 370||TENSION SPRING, Choke Return||2|
|13 11 1 335 318||FLOAT NEEDLE, Rubber Seal||2|
|13 11 1 335 320||CLAMPING SPRING, Float Needle||2|
|13 11 1 335 324||SPRING (to 10/84), Slide||1|
|13 11 1 337 358||SUPPORTING RING, Slide||1|
Since parts are missing on my carburetors, I didn’t have to remove all the parts. Here is how I disassembled the 1983 R100RS carburetors which is put together the same as the 1983 R80ST carburetors I am using.
Here are some pictures of the R80ST disassembled carburetor. Not all the parts are there.
Cleaning and Polishing
I start by soaking the carburetors in Chem Tool carburetor cleaner over night. To restore the finish on the carburetors takes a lot of elbow grease and patience, but the result is worth the time. This section from my rebuild of my 1973 R75/5 carburetors provides the details of how I do this for carburetors.
Here are some before and after pictures of the R80ST carburetors.
Rebuild Kit Parts
EME supplies a carburetor rebuild kit. I added new floats, float needles, float pins, main jets, needle jets and jet needles as well. Here is a description of the kit from the 1983 R100RS 40 mm carburetors which has the same types of parts as the 32 mm R80ST carburetors, but the diaphragms are different since the R100RS has 40 mm carburetors.
The assembly procedure for the 1983 R80ST carburetors is the same as for the 1983 R100RS carburetors.
Here are the jet sizes, needle clip position and idle mixture screw turns I am starting with.
- Main Jet: 150
- Needle Jet: 2.66
- Jet Needle: 241
- Idle Jet: 45
- Needle Pstn: #3
- Idle Mixture: 0.5 Turns
Here are some pictures from the assembly of the R80ST carburetors
Repaint Carburetor Emblems
The white paint was gone on one of the carburetor emblems and was faded and missing is some spots on the other carburetor. So I repaint the emblems. I use pinstripe white paint. I make a stamp out of small piece of balsa wood. I paint one side of the balsa wood and then press the painted side on the emblem to apply paint to the raised part of the emblem. There are some nicks in the emblem and low spots. I use a round tooth pick to fill those in with the with paint. And, some small spots of paint ended up on the black emblem, so I used a razor blade to scrape them off.
When the paint had dried over night, I used some Forever Black to touch up the black areas of the emblems. If I get some on the white paint, it can be cleaned off with a clean blue shop towel before it dries.
What Done Looks Like
Here is the rebuilt and refinished carburetors.
2022-10-30 Corrected info about the carburetor model used on all R80ST US bikes.
2022-11-03 Correct Missing-Damaged parts list.
Thank you Brook for another very detailed explanation/teaching of these carburetors! Your videos of this very important project are amazing too! Again thank you for taking the time and work to show us how to work on our own beloved Airheads.