Electric starter problem

Discussion in 'Airheads' started by d_mpls, Jun 2, 2012.

  1. d_mpls

    d_mpls Adventurer

    Apr 8, 2012
    44°59′N 93°16′W
    Hello everyone, the bike in question is a 1973 R75/5

    Primary symptoms / observations:
    Electric starter not working 8 out of 10 times
    - electric starter more likely to work if the bike is hot, after a short pause for example.
    - upon pushing the starter button, no under tank sound from the relay, everything is completely silent
    - all lights and horn working with ignition on
    - kick starter works and starts the bike, the bike runs well otherwise.

    Secondary symptoms / observations
    - headlight sometimes is dim
    - with the headlight on, on two occasions (not always), i have smelled burnt plastic/rubber coming from the engine block/under tank area. I'm not using the headlight at the moment for precaution.
    - a while ago, i had a major electric failure, all lights out, brought the bike to a mechanic that fixed everything. He said the issue was improper wiring in the headlight bucket.

    Done so far:
    - Checked battery: good voltage at idle and at higher rpm.
    - Removed tank and inspected wires: no damaged wire found, no corroded wires found, no disconnected wires found.
    - Cleaned all connections of the starter relay sockets. No corrosion on the wire themselves, some white dust on the bottom of the relay.
    - Checked inside the headlight bucket: no damaged or disconnected wires
    - Removed starter button cover: found a spider nest from 1979, cleaned it and put it back together, all the wires seemed fine.

    Research done.
    I have read this http://bmwmotorcycletech.info/startingprobs.htm a few times, and point number 9 describes my situation. My problem is that i have zero knowledge of electricity and i cannot really perform the test unless someone guides me step by step.

    Question for you guys:
    - If you think that there is anything else i should check other than the relay, please let me know
    - Could you guide me in the testing of the starter relay, and in general in the testing of other parts, like for example the starter button? I need pretty literal directions, consider that i have never used a multimeter before, so please be as specific as possible. I know how to get to the relay, i need guidance in the testing part.

    Today I have purchased a multimeter, I have a clymer manual with electric diagrams in color, i have time and i want to learn. Worst case scenario I want to be able to bring the bike to a mechanic and tell him what i have done and possible save some money.

    Sorry for the super-long post.
  2. Houseoffubar

    Houseoffubar HoFmetalworks.com

    Dec 4, 2010
    Bothell, Washington
    $10 says, pull the starter, clean the armature, check the brushes, and grease the bushings a bit, and she will work like a champ!
  3. oldroadie

    oldroadie Two wheel addict

    Feb 28, 2010
    North Alabama mountains
    I had a sluggish, intermittent starter on my 72 R75/5. After installing new bushings (the brushes still had plenty of meat) it still did not perform well. Turned out to be the solenoid, the copper contactor plate was severely pitted and needed dressing with a file. If you're not good with electrical you won't be good at unsoldering the solenoid...

    So, do you get a big click or a little click when the starter fails? That will clue you as to which (relay or solenoid) component is failing. If you don't get the big click the relay is likely at fault. Big click and no starter implies the solenoid. A 73 starter is going to need new bushes, the kit with bushes and brushes isn't much money but you do have to solder to install it. You need a friend who's handy with a multimeter and a soldering iron.
  4. Wirespokes

    Wirespokes Beemerholics Anonymous

    Jul 26, 2002
    Jackson's Bottom Oregon
    With no click at all, it's either that the starter relay isn't functioning, or it's not getting power due to bad connections, or the upstream source failed.

    Do you know where the starter relay is located? Left side of frame just back of the headstock. You'll have to remove the tank to get to it.

    First step is to pull it out of the socket and clean the contacts. Get some electrical contact cleaner or some sort of chemical metal cleaner and make the connections bright and shiny.
  5. Bill Harris

    Bill Harris Confirmed Curmudgeon

    Sep 20, 2008
    backwoods Alabama
    Remember, this bike is a /5 and there is no socket to the starter relay (the big, expensive interlock one). No clickee implies a bad relay or something upstream is amiss.

    Methinks this may be related to "major electric failure, all lights out, brought the bike to a mechanic that fixed everything. He said the issue was improper wiring in the headlight bucket" and he needs to have that wrench look at it.
  6. MNrider

    MNrider Local tall guy.

    Sep 7, 2008
    Raymond Washington
    Or, take it to the starter rebuild place on University Avenue in St. Paul.
  7. d_mpls

    d_mpls Adventurer

    Apr 8, 2012
    44°59′N 93°16′W
    thanks everyone for the help. two airheads friends came over and helped me diagnose the issue. After testing the wires and experimenting with all sorts of combinations, the consensus seems to be that i have a faulty starter relay. Or, like one person suggested here, at least we know that the issue is upstream. I have ordered one relay, so hopefully that will solve the issue.