I just wanna ride 1970 BMW R50/5

Discussion in 'Airheads' started by crawler07, Jun 23, 2019.

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  1. crawler07

    crawler07 Been here awhile Supporter

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    Hi all,

    I found a Craigslist BMW R50/5 and thought I really need another bike in my life. I bought this bike knowing very little about BMW motorcycles I have worked on alot of motorcycle over the years Honda, Yamaha, Kawasaki, Suzuki,Triumph, A few HD's but this is the first BMW I have ever had my hands on.

    Met the seller and struck a deal, took the bike to my garage and started looking it over. When the guy started it up for me it was making a pretty loud clacking from the left side cylinder I thought it would either be Piston slap or need a valve adjustment (the seller said he just adjusted the valves) But he also said he cleaned the carbs and they were filthy on the outside and and inside the bike was very difficult to start and didnt want to idle.

    The bike also had no brakes front or rear, tires were dryrotted fork boots were torn, front forks were dry. I have rebuilt the forks, installed new brakes front and rear as well as new tires and cleaned the carbs which brings me here. Big surprise somone needing help with BMW carbs......

    I removed all jets, and soaked all components including the carb housings and float bowls in carb cleaner. As I was breaking the carbs down I noticed that the idle jets were different one carb was a 35 and the other carb was a 45. I ordered another 35 and installed it along with new floats, float needle and pins, new float bowl gasket. I set the floats to be level with the bowl seam. As I was cleaning the carbs I noticed that one carb has a blockoff plug (brass) in one of the ports on the cylinder side and the other has two open ports. One carb is marked as 1/26/114 and the other is 1/26/113. I can upload a pic if needed, so is this the way its supposed to be? With these carbs being so tough to tune and sync I would think they should be the same...

    I have reinstalled the carbs and still cant get it to idle properly it will idle up high then drops down and will die if I dont hit the throttle. I started out by setting the mixture screw at 2 out and the idle screw at 1/2 turn out.

    The previous owner had installed a dyna III elec ignition module, I was thinking maybe the advancer isnt working so I will take the front cover off and check it, but it shouldnt prevent idle should it? I have not checked timing but will I guess it could cause issues?

    Sorry for all the info, just didnt want to waist to much of your time by slow feeding the info.

    Oh I did do a comp check with carbs off, it was 135 on the right cyl and 140 on the left.

    I will also check the valves and replace, spark plugs and the throttle cables.

    If there is anything else I should look into please let me know any and all help is appreciated!
    #1
  2. Big Bamboo

    Big Bamboo Aircooled & Sunbaked

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    Make sure the timing is correct and valves adjusted before attempting to adjust the carbs, other than a base setting. Any adjustments to the carbs should be made after the bike is up to operating temp. Here's a list by Tom Cutter that I do to any new to me bike. It helps to establish a baseline. Steps #8 through #14 do not apply to your slide carbs, except the play in the cables.
    1) Change ALL oils.

    2) Torque cylinder heads (25 foot pounds, loosen each nut 1/2 turn,
    then torque, use crisscross pattern)., adjust rocker arm end play (zero
    play, no rotational binding), adjust valve clearances (cold engine) to
    .006" Intake, .008" Exhaust.

    3) Service auto advance unit (don't snap the thread off the end of the
    cam, tighten GENTLY!), grease point cam felt with a smear of grease.

    4) Set points gap to 0.016" (0.40 mm) using a good feeler gauge, or
    better yet a dwell meter, look for 39 degrees on the four cylinder
    scale (gives you 78 degrees on a two cylinder).

    5) Set ignition timing static setting to S mark on flywheel.

    6) Check full advance timing at 3200 RPM, the dot (or hole if the paint
    is gone) above the F mark should be steady in the center of the timing
    hole (or Z mark on later models) , aligned with the machined groove in the side of the hole.

    7) Service the air filter, i.e., put a new one. DO NOT blow out air
    filter with compressed air, do not leave a K&N filter in at all.

    8) Drop carb float bowls and clean the tiny jet in the little well in
    the corner of the bowl using a single strand of wire from a wire brush,
    held with needle nose pliers. Make sure contact cleaner will spray
    through the jet into the bowl.

    9) Remove the main jet and jet holder (make a mental note of the depth
    of engagement of the jet holder), drop down the needle jet and emulsion
    tube, (keep your finger over the hole so they don't fall out and get
    lost.) Use some Gumout carb cleaner spray to clean the gunk that has
    accumulated above the jet holder. Spray the jets and emulsion tube
    clean, then reinstall the emulsion tube, needle jet and jet holder.
    Visually align the jets onto the needle carefully. As you screw the jet
    holder up in with your FINGERS, if it doesn't seat fully (remember the
    mental note?) then back it up about 1/32 of a turn and wiggle it as you
    screw it in gently (FINGERS ONLY!) You will feel when the emulsion tube
    finds its way up into the carb body hole. If you can't get it , remove
    the air tube from the air cleaner housing and visually see that the
    emulsion tube projects up into the venturi about 3-4 mm. You can wiggle
    the needle to help align it as you screw it up in with your FINGERS.

    10) Check the float level setting by lifting the float gently with your
    fingers. When the needle seats, BEFORE the spring loaded part begins to
    depress, the seam in the float should be parallel to the float bowl
    gasket surface. Reinstall the bowl carefully, making sure the gasket is
    fully seated in the groove all the way around.

    11) Check that the throttle cable has a tiny amount (1-2mm) free play
    when the throttle grip is all the way back. Get the two sides as close
    to the same free play as possible.

    12) Check that the choke cable fully seats the lever on the post when
    the lever is in the horizontal position. At half choke, the lever on
    the carb should be halfway between the posts. At FULL choke position of
    the hand lever, the choke lever should be all the way up to the top
    post.

    13) LIGHTLY screw the idle mixture screw IN gently until you just feel the screw
    seat. Now back the screw OUT by 3/4 turns (this setting varies for
    other models).

    14) Turn the idle SPEED screw OUT until it does not contact the
    butterfly lever at all. Now screw the screw IN until it JUST touches
    the lever, now turn it IN one FULL turn.

    These are the baseline settings. Now take the bike for a LONG test
    ride, at least five miles, to get it to FULL operating temperature.
    Riding around the block or starting and revving on the stand will NOT
    work.

    At this point you need to synchronize the carburetors. This is
    accomplished either by shorting one cylinder at a time (this takes some
    practice to get right, usually you need somebody to show you once) or
    using a vacuum gauge on the vacuum takeoff ports on the side of the
    carb. Set the idle mixture on each carb at the point that gives best
    running, usually between 1/2- 1-1/4 turn out. Balance the idle speed
    screws, then balance the cable pull off idle. Recheck to be sure that
    you still have a tiny bit of free play of the cables. If not, readjust
    the cables.

    This should get the bike running pretty well. Idle speed should be
    at 1000-1100 RPM. DO NOT set the idle for a super low "tick over", as
    this will severely reduce oil circulation in the engine and make the
    transmission rattle like a bag of rocks. (edited for spelling and Z mark comment)
    #2
  3. crawler07

    crawler07 Been here awhile Supporter

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    Wow great reply!!! I will indeed start with the Valves and Timing and advancer. Once I complete all these tasks I will set the idle screw up as suggested and turn the mixture screw out 3/4 at that point even if the bike wants to stumble and pop I should just take it for a 5 min ride without tuning first?
    I failed to mention that when I would get it to run, it would take throttle while in neutral but when in gear it would begin to accelerate then fall on its face and bog out no matter how I feathered the throttle and would not even pull me up my driveway (15% grade) Im assuming once I get the timing correct advancer working properly and the valves taken care of it shouldnt do any of this??
    #3
  4. Big Bamboo

    Big Bamboo Aircooled & Sunbaked

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    Yes, getting the timing advance unit functioning properly is critical for good running. Make sure you disconnect the ground cable before removing the front cover, or you risk shorting the diode board. It's a good idea to buy a strobe timing light. It's the only way to be sure the advance unit is functioning properly. He is describing different carbs than yours. They are not set the same way. Someone with more experience with slide carbs should chime in shortly. Do you have any manuals? Here is an online owners manual, with lots of good information: https://www.pbase.com/dwerbil/slash_5
    #4
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  5. chasbmw

    chasbmw Long timer

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    Some of these instructions are for the CV carbs on the bigger later bikes, the R50 uses slide carbs, won’t have vacuum take off ports as standard etc etc. Take a look at generic instructions for tuning slide carbs or seek advice from the /2 thread on this forum.

    When running properly should be a very sweet smooth bike (but slow)
    #5
  6. crawler07

    crawler07 Been here awhile Supporter

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    Wow thanks for all the help fellas! Bamboo I really appreciate the owners manual link that will come in handy! Chasebmw I im not to interested in going fast any more, just want to cruise with the wife. I hear alot of people saying how slow these are but im sure it will have enough oomph to haul 2 people around right?
    (2 small people)
    #6
  7. tlub

    tlub Long timer Supporter

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    A couple of other things. The right and left are different numbers, 1 apart. Call Bing for what they are supposed to be. From what you saw I suspect the needle jets might be too lean. In the old days before oxygenated fuel they ran leaner. While you are on the phone get needle jets one size larger than stock (i.e. 2.68 if the stock is 2.66). Also be sure the spring loaded acceleration jets with the 3 hole, built into the main/needle jet assembly, is intact and clean. If you dumped the assembly into carb cleaner you probably need some new parts there too.
    If these are original/5 carbs they will have a tickler for starting (a knob to depress the float, temporarily flooding the bowl), not a choke (actually an enriched whis is a built in rich running mini carb for starting) If you're not familiar with both of these, meaning you didn't ride 1960s bikes regularly, you have a learning curve ahead of you.
    They both work fine when properly used by a knowledgeable person. A knowledgeable person is NOT one that has always thought fuel injection is 'normal' .
    If you have the enrichers rather than the ticklers, you have R60/6 carbs and they will work but need to be rejetted.
    If all this sounds like Greek to you, and you can afford it, I might suggest you have Bing rebuild them.
    #7
  8. Pokie

    Pokie Just plain Pokie.

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    If the bike starts readily, the timing is fine. Do a proper valve adjust (sounds like the previous owner didn't rotate the engine before setting the other side), check the oil then take it for a ride. From there do work as required, don't go looking for trouble, trouble is what you will find!
    #8
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  9. crawler07

    crawler07 Been here awhile Supporter

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    Bing will know what jetting I should run? Or whats stock for this year/model? I took apart the emulsion tube completely before soaking it cleaned all the debris out and reinstalled all parts according to the carb breakdown chart I found online. The only thing a little questionable was that the spring inside the acceleration jet was different lengths between the 2 carbs (maybe 3mm diff) Yes these have a tickler, I have used a tickler equiped carb before not on a motorcycle but a wood chipper I once owned that ran an old Tecumseh engine so not to intimidated by them. And I have never owned a fuel injected bike:nono
    #9
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  10. crawler07

    crawler07 Been here awhile Supporter

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    Pokie, Thanks for the reply Im with ya (don't go lookin) I was getting so wrapped up in all this BMW is a black art thing that my wife kept asking me whats wrong, whats wrong for days than out of nowhere said are you mad at me?? I said no just been thinking about this darn BMW
    #10
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  11. JGT

    JGT Been here awhile Supporter

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    I've got a R50/5 as well. Regarding two-up capacity, it can do it but not well. Pulling away from stop signs is slow, as is stopping at them again after you are going. I feel much more comfortable on the bike when just myself on it.

    All that said, if you practice and don't want to go too fast then it can work. Braking really is harder with the weight of two riders. And my bike is set up well, I think -- new brake shoes, everything adjusted correctly, etc.

    But the R50/5 is rare! Resist the urge to "upgrade" it to larger cylinders -- better to just sell it and buy a R75/5 if that ends up being what you truly need. (Although the brakes on the R75/5 are the same...)
    #11
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  12. crawler07

    crawler07 Been here awhile Supporter

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    IMG_2870
    IMG_2869
    IMG_2824

    Well here she is in all her glory! Looks like every other R50 but this one is mine....

    The 2 carb pics show how one has an extry port, wondering if that is correct? Seems like it could make it a little more difficult to tune...
    #12
  13. crawler07

    crawler07 Been here awhile Supporter

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    I guess I will just have to give it a go once its up and running properly (Need to get that front brake adjusted properly first) and see what it feels like. I have a Honda CB350 that hauls us around pretty decent so we will see. Oh I didnt mention I live in the hills of WV so that may not help matters:D
    #13
  14. tlub

    tlub Long timer Supporter

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    Yes, Bing should know. They are pretty helpful on the phone. I would guess 3mm is not a big deal, but you may want to freshen that up as well. These 'accelerator pumps' are not so much pumps as dribblers, but they do get more fuel in the throat, and the air stream atomizes it, so it does work. You may need to have it thoroughly warm to not stumble if they aren't working, and even then patience is a virtue when it comes to speed of throttle opening. One way to test is tickle them to near flooding and then try getting up the drive. If that fixes it, its the pumps, the needle jets, or it just was not warmed up enough. The difference between the chipper and the bike is that the bike throttle is manipulated by you; the chipped probably has a slower opening rate and may not be so critical on mixture.
    Plus, all these need a slightly richer mix if you are running an oxygenated fuel (10% ethanol).
    One more thing to check is if the fuel levels actually are the same, and where they should be. If the floats or float needles/seats are in slightly different shape, the resultant levels may not be identical. It doesn't take much to make a difference.
    Were the needle jets the same side to side? If the idle jets were not, I wonder about the others.
    Good luck!
    #14
  15. robtg

    robtg Long timer

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    The R50 will be a bit more comfortable for 2 up but don't expect any more power. If the CB worked for you the R50 should be fine.
    #15
  16. PaulBarton

    PaulBarton Long timer Supporter

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    Just to be clear...NOONE buys an R50/5 to go fast.
    #16
  17. 2WheelTraveler

    2WheelTraveler backinthesaddleagain Supporter

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    Regarding the performance of the /5 in particular the R50 its not a screamer, but it is a fun bike especially the SWB . With the 4-speed transmission the steps between gears are pretty big. I've found installing a final drive with lower gearing helpful, at least for a town bike. You loose a little off the top, but it gets you off the line quicker and up the hills easier. It's a relatively easy swap and the lower geared final drives are available and inexpensive.
    #17
  18. PaulBarton

    PaulBarton Long timer Supporter

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    I have a SWB R75/5 and it is a fun bike. The thing to remember with a rear drive swap is that the speedo is mated to the rear drive. You need to swap the speedo (or have it modified) for the correct ratio to keep it "accurate". I thought the R50/5 came with the 37/11 rear drive...
    #18
  19. Big Bamboo

    Big Bamboo Aircooled & Sunbaked

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    Your pics are not showing for me. Instead of hosting them on another site, use the "Upload Pic" tab at the bottom of the post, and you can pull them directly off your computer.
    #19
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  20. bpeckm

    bpeckm Grin! Supporter

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    The two carb numbers are because they are different L&R. According to the MAX fiche, you do have the right carbs. I had the tickler carbs some time ago, I do remember that the idle mixture for the slide carbs does the opposite of the diaphragm carbs (one does air, one does fuel but don't remember which is which!). Regardless, the principle is the same: adjust to the fastest it will go and then back off a quarter turn. They are very simple carbs and should be easy to adjust reasonably well even without the vacuum ports of the diaphragm carbs.

    The Bing "bible" book is a worthwhile investment, especially once you've had a couple of different models....

    ...and as to riding two up, hey some folks do it on 49cc scooters....it's all in what you expect to do. For bimbling about the countryside, the 500 will do just fine. The 500 is a sweet and smooth engine. It does take getting used to if you're used to rocket-riding, though!

    :D
    #20
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