Hey there! I picked up a ‘71 R75/5 a couple weeks ago and have been working on getting it on the road. I have gotten to a point where I no longer know what to do next.
It ran when I bought it, but poorly and hadn’t been on the road since 2008.
Symptoms
Bike starts almost instantly without choke when “cold” runs well and consistent but with some white/black smoke. Once it comes up to temp (maybe 3-5 min of idling) the idle slows down and eventually it completely dies. After letting it cool down for 5-10 min it will start back up no problem. And then die again when warm. If I try to restart it immediately I can get it to kind of “run” on one cylinder with the throttle about halfway open or more.
Things I have done:
Ignition - New points, condenser, cleaned advance and installed new springs, new coils, spark plug cables, and spark plugs. Oil and filter change.
Fuel - Rebuilt both carbs (cleaned/blew out all passageways, all new o rings, new idle jet, float needle, float, diaphragm and needle, and new gaskets)
New fuel lines, filters and cleaned out petcocks. New throttle cable and choke cables
Air - New air filter, new rubber carb to cylinder head coupler.
Troubleshooting
Immediately after dying turned off fuel taps and check carb bowls for fuel, both have fuel, and float levels have been set to the proper level.
Immediately after dying pulled plugs and checked for spark. Both cylinders have good spark. Spark plugs are quite sooty and seem to be running rich.
Checked/ adjusted valves and re-torqued heads.
Set points gap and using timing light I see “s” is in the window at idle and the advanced mark is showing when revved to 3000 and above.
Validated chokes are truly off when intended and installed correctly.
Adjusted carb to base settings then adjusted for best running, which seems to be mixture screw almost completely in. Also moved carb needles from position 2 to position 1 (longest) in effort to lean out mixture and that did seem help to cut down on smoke and improve running slightly but it still dies.
Adding choke while it’s running immediately kills it.
Validated idle jets are 45s and both main jets are 140s.
Carbs are Bing 32MM 64/32 - 3/4
At this point I’m just going back though everything I did again, but am only increasing my frustration because with each thing I check I’m validating that it should be running fine.
Any help or insight would be very appreciated, this is my first BMW Airhead so there’s a lot I have still to learn. But I am familiar with VW airheads and basic mechanics in general.
Thanks!
It ran when I bought it, but poorly and hadn’t been on the road since 2008.
Symptoms
Bike starts almost instantly without choke when “cold” runs well and consistent but with some white/black smoke. Once it comes up to temp (maybe 3-5 min of idling) the idle slows down and eventually it completely dies. After letting it cool down for 5-10 min it will start back up no problem. And then die again when warm. If I try to restart it immediately I can get it to kind of “run” on one cylinder with the throttle about halfway open or more.
Things I have done:
Ignition - New points, condenser, cleaned advance and installed new springs, new coils, spark plug cables, and spark plugs. Oil and filter change.
Fuel - Rebuilt both carbs (cleaned/blew out all passageways, all new o rings, new idle jet, float needle, float, diaphragm and needle, and new gaskets)
New fuel lines, filters and cleaned out petcocks. New throttle cable and choke cables
Air - New air filter, new rubber carb to cylinder head coupler.
Troubleshooting
Immediately after dying turned off fuel taps and check carb bowls for fuel, both have fuel, and float levels have been set to the proper level.
Immediately after dying pulled plugs and checked for spark. Both cylinders have good spark. Spark plugs are quite sooty and seem to be running rich.
Checked/ adjusted valves and re-torqued heads.
Set points gap and using timing light I see “s” is in the window at idle and the advanced mark is showing when revved to 3000 and above.
Validated chokes are truly off when intended and installed correctly.
Adjusted carb to base settings then adjusted for best running, which seems to be mixture screw almost completely in. Also moved carb needles from position 2 to position 1 (longest) in effort to lean out mixture and that did seem help to cut down on smoke and improve running slightly but it still dies.
Adding choke while it’s running immediately kills it.
Validated idle jets are 45s and both main jets are 140s.
Carbs are Bing 32MM 64/32 - 3/4
At this point I’m just going back though everything I did again, but am only increasing my frustration because with each thing I check I’m validating that it should be running fine.
Any help or insight would be very appreciated, this is my first BMW Airhead so there’s a lot I have still to learn. But I am familiar with VW airheads and basic mechanics in general.
Thanks!