71 R75/5 dies when warmed up

[cvhd94]

Yes, I did get new non resistor plugs and wires, and new coils as well. Just tested and got about 19,300 ohms.

Yeah it’s a new paper filter, not K&N. It’s definitely clean and clear, blocked one end and blew on the other just to see if there was any resistance at all and it felt like there wasn’t even a filter there, so I don’t think that’s it.

 

[cvhd94]

Well, I don’t want to speak too soon, but I think I made some good progress again!

Took both carbs off again, and completely disassembled them for a fourth time, cleaned and blew out every passage and jet, and put it all back together. I installed a one step leaner needle jet and main jet while I was at it as well. Then put the carbs back on the bike and fired it up. It did still start without choke, but I did run it earlier in the evening.

But it ran great, no more mush at the low end when starting to apply throttle, and when it settled right back into an idle without acting like it was going to die. I was elated and wanted to take it for a spin to see if it was just a fluke.

I turned on my headlight and started backing out of the garage, when I looked forward again I saw smoke pouring from the headlight. I guess you can’t win them all. After quickly turning off the bike, disconnecting the battery and inspecting the damage and cursing the PO’s shoddy botch job that he called wiring. I made sure to insulate anything that got singed and put the headlight cover back on because damn it I was going for a ride, lights or not.

It ran great, I didn’t go very far, or for very long on account of not annoying my neighbors at 9:30pm. So I made it back to the garage and let it idle some more, turned it off, turned it back on. Then did it again to celebrate.

Will try my luck again tomorrow, fingers crossed it wasn’t a Guinness induced fever dream.

 

[kinterridge]

Great news on getting it running on the fuel side of things. If your harness is bad in the headlight, I recommend checking all the wiring and grounds. If the harness is beyond repair, Britts and Beemers Motorwerks makes harnesses up through /5 bikes. (He used to supply to Bench Mark Works their harnesses.)

 

[stevenrankin]

Considering

Well, you had a large list of stuff you did and for sure karma will stick a finger in and mess up one item on the list. But as you find, rechecking things and not giving up works in the end. Maybe in this case the needles were just in the wrong place.

As for the smoking headlight, yeah, if I recall, some of the early /5 bikes didn't have fuses which led to bad things. I am saying a prayer to the god of wiring things are minor in your case.

Kit, thanks for the link to Brits and Beemers, I know my shop owner friend will be interested. So far the only place we have found harnesses has been from EME and to be honest I don't know if they sell /5 harnesses or not. It is always good to have a second source.

Enjoy the riding. St.

 

[44006]

"Things I have done:

.......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)....."

71 R75/5 does not have large diameter push down spring on top of carb slide
Slide must drop by gravity with freefall and click when hits bottom
There are new diaphragms out there that are too stiff to work without pushdown spring
Impossible to tune bike if slides do not fall freely and sharply to bottom when throttle closed

Run bike without air tubs and confirm slides fall completely every time you blip throttle
Stiff diaphragm will hold slide up when you stop warm and not fall till bike cools

Will drive you nuts!

I did not read every post so forgive me if I missed something

 

[stevenrankin]

Again, don't forget to make sure your valves are adjusted. Tight valves can cause poor idle or stalling as well as poor performance. St,

 

[beemerguru]

The scattergun approach is always hit or miss.

Any airhead with over 30K miles will need a full carb rebuild

Before working on the carbs, first check the valve clearances.

Now the carbs.

Take the carb top off. Check the diaphragm for stiffness or small holes. If it is pliable and free of holes, you may reuse or replace it —your choice.

Hold the carb top in the light and use a magnifying glass to examine the needle. It might look like the surface of the moon, with tiny pits. If pits, replace.

Pay attention to how many clicks you hear/feel as you twist the needle and pull out of the top. Usually three. The new needle goes in the same number of clicks

The needle jet has had the needle bouncing around inside every time the needle goes up and down when you twist the throttle. The needle wears the needle jet, which changes shape.

Between the pits on the needle and the ovaled-out needle jet, the air/fuel mixtures move slowly away from the factory spec..and change the way the engine reacts to throttle changes.

A new needle and new needle jet will bring the carb back into its original function.

The O rings on the idle jet and air/fuel mixture screw will probably crack and fall apart when you try to remove them..or if someone used the wrong size O ring..they can be flattened against the side. You want to use the SMALLEST O rings in the kit for the idle jet and air/fuel mixture screw..

It's not that often that the butterfly shaft O rings need replacing. If you decide to change them, read up first on the disk orientation and how to peen the little screws.

Install a new bowl gasket and put the carbs back on the engine. Start with the air fuel mixture 3/4 of a turn out from seated.

Gas on, and start her up. Adjust the throttle screws so she doesn't die...and go for a potentially crappy 5-mile ride with stops, acceleration, and a decent long warm-up straight before getting home and the engine off. Have a screwdriver and 10mm, 8mm, and 7mm wrenches right there. If you have a Twin-Max or other way to measure the vacuum ...good. If not, you can usually get close enough by paying attention.

At home, bike on the center stand and check the free play on both choke and throttle cables. For the /5, move the choke lever down and watch if both choke levers move all the way up. Pull the choke lever all the way back up and check that both choke levers are actually all the way down by pressing on the lever with your finger or screwdriver.

Hook up the twin max or carb stix.

Now start the engine and slowly turn the air-fuel, mixture screw in until the engine slows down, then back out while the engine speeds up...keep going, and the engine should start slowing down. Find that happy place where the engine is at the highest speed. Now, do the same for the other side.

Now the throttle screws...probably idling at 2K+, so slowly back out the throttle screws a little at a time..may be going from one side to the other.. until the tach (if it's working) is around 1K rpm, - or watch the charging light when it comes on instead. Idle should make the charging light JUST go out.

Balance the carbs using the tool.

OR, if you pay attention...VERY slowly turn the throttle maybe 5mm...just enough to get it off idle. You can tell right then if the two sides are close or fighting each other..The engine is smooth or you can feel a vibration as one side pulls harder than the other.

If the engine is vibrating, hold the throttle at that position and gently pull up on each throttle cable one at a time. See what change made the engine smooth out. Either more or less throttle on one side usually does it.

Try the small throttle a few more times and you should be able to tell if you have a smooth engine...add a little more throttle and the feeling should stay smooth - or make SMALL adjustments to get it close. Now tighten the 10mm throttle nut and go for another ride.

You'll get better with experience..or if this doesn't make sense, find another airhead with the balancing equipment or attend an Airhead Tech Day and learn

 

[Lendog]

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!

going back to the carbs is likely the place to start, last year I tuned my Guzzi, had issues, I go back thru and find new condenser’s defective,
I went as far as removing a cylinder head considering valve issues, well worth the efforts you hopefully will feel later as I do every time I ride

 

[Lendog]

The scattergun approach is always hit or miss.

Any airhead with over 30K miles will need a full carb rebuild

Before working on the carbs, first check the valve clearances.

Now the carbs.

Take the carb top off. Check the diaphragm for stiffness or small holes. If it is pliable and free of holes, you may reuse or replace it —your choice.

Hold the carb top in the light and use a magnifying glass to examine the needle. It might look like the surface of the moon, with tiny pits. If pits, replace.

Pay attention to how many clicks you hear/feel as you twist the needle and pull out of the top. Usually three. The new needle goes in the same number of clicks

The needle jet has had the needle bouncing around inside every time the needle goes up and down when you twist the throttle. The needle wears the needle jet, which changes shape.

Between the pits on the needle and the ovaled-out needle jet, the air/fuel mixtures move slowly away from the factory spec..and change the way the engine reacts to throttle changes.

A new needle and new needle jet will bring the carb back into its original function.

The O rings on the idle jet and air/fuel mixture screw will probably crack and fall apart when you try to remove them..or if someone used the wrong size O ring..they can be flattened against the side. You want to use the SMALLEST O rings in the kit for the idle jet and air/fuel mixture screw..

It's not that often that the butterfly shaft O rings need replacing. If you decide to change them, read up first on the disk orientation and how to peen the little screws.

Install a new bowl gasket and put the carbs back on the engine. Start with the air fuel mixture 3/4 of a turn out from seated.

Gas on, and start her up. Adjust the throttle screws so she doesn't die...and go for a potentially crappy 5-mile ride with stops, acceleration, and a decent long warm-up straight before getting home and the engine off. Have a screwdriver and 10mm, 8mm, and 7mm wrenches right there. If you have a Twin-Max or other way to measure the vacuum ...good. If not, you can usually get close enough by paying attention.

At home, bike on the center stand and check the free play on both choke and throttle cables. For the /5, move the choke lever down and watch if both choke levers move all the way up. Pull the choke lever all the way back up and check that both choke levers are actually all the way down by pressing on the lever with your finger or screwdriver.

Hook up the twin max or carb stix.

Now start the engine and slowly turn the air-fuel, mixture screw in until the engine slows down, then back out while the engine speeds up...keep going, and the engine should start slowing down. Find that happy place where the engine is at the highest speed. Now, do the same for the other side.

Now the throttle screws...probably idling at 2K+, so slowly back out the throttle screws a little at a time..may be going from one side to the other.. until the tach (if it's working) is around 1K rpm, - or watch the charging light when it comes on instead. Idle should make the charging light JUST go out.

Balance the carbs using the tool.

OR, if you pay attention...VERY slowly turn the throttle maybe 5mm...just enough to get it off idle. You can tell right then if the two sides are close or fighting each other..The engine is smooth or you can feel a vibration as one side pulls harder than the other.

If the engine is vibrating, hold the throttle at that position and gently pull up on each throttle cable one at a time. See what change made the engine smooth out. Either more or less throttle on one side usually does it.

Try the small throttle a few more times and you should be able to tell if you have a smooth engine...add a little more throttle and the feeling should stay smooth - or make SMALL adjustments to get it close. Now tighten the 10mm throttle nut and go for another ride.

You'll get better with experience..or if this doesn't make sense, find another airhead with the balancing equipment or attend an Airhead Tech Day and learn

as a lifestyle no one touches my bikes (or tools) however, I would allow this guy the freedom

 

[olironrider]

… in regard to Post #45: the springs mentioned for helping return the slide to idle in the Type 64, 64/32/9-10 carburetors, are the ones installed in the Type 64-3, 64/32/357-358 carburetors: Part Number 60-306, surely available from BING Agency.

Not a particularly fast & easy fix as, in order to install them, you have to disconnect the throttle and enricher cables (don’t try to fully remove the nut on the clamping bolt of the enricher cable at the lever; only a enough turns off to free the enricher wire as the very end of that threaded bolt is crimped to prevent the nut from falling off… you’ll break the bolt !), then the carburetor top cover can be removed.

Of course, the springs go in above the diaphragm and under the top cover. If you are observant and careful during disassembly, noting the positions of the throttle and enricher adjusters, there might not be a need to reset them following assembly.

Those 60-306 springs made a world of difference on my 64/32/9-10s !

 

[98lee]

Bike starts cold and quits when warmed up - classic behavior for engine with little or no valve tappet clearance.

I agree that that is the classic symptom of valves being too tight. That was my first thought before I read the rest of his post.

Bike sat for many years - no mention of adjusting valve clearance since purchase.

Read post #1 by the OP under Troubleshooting. Line three. Well, there goes that idea.