Chasing a problem, need some advice on grounds on 1974 airhead

Discussion in 'Airheads' started by mfp4073, Sep 27, 2018.

  1. mfp4073

    mfp4073 Long timer

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    Ive been chasing this problem for over a year and unable to ride the bike. Early 1974 R90/6 with 125k miles. What i want to do is to check the grounds as its been recommended to me that might be a problem. I need to know where/what to check on the bike for grounds other than the obvious place at the battery....below I will explain how i got to here

    Bike started getting a slight miss at constant speed/throttle noticeable at 45-50 mph plus. At constant speed you will feel it lose power slightly, several times a second sometimes and the front of the bike will drop slightly. I can ride it at neighborhood speeds with no problem. starts and idles fine. So far I have:

    reset points
    resynced carbs
    readjusted valves
    changed plugs
    swapped out coils (for others I have on the shelf)
    swapped out plug wires (for others I have on the shelf)
    carbs removed, cleaned, tore down, inspected, checked for leaks
    retimed with timing light
    replaced points/condenser
    (I feel like im forgetting some items here and will edit them in as I remember)
    replaced fuel filters
    Gas tank inspected, flow tested
    dumped fuel, fresh gas, then upped to 94 octane
    neg battery cable replaced and mounts to the engine, not frame
    Compression test shows 150 left 120 right, added oil to right side, retested only increased to 125



    grounds are easier to check, next up will be pulling the front off the motor and checking/replacing the timing set (chain/gears).
    #1
  2. mfp4073

    mfp4073 Long timer

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    ive never heard of this test. there are 2 coils, would I need to jumper both of them?
    #2
  3. beemerphile

    beemerphile Unreconstructed Southerner Supporter

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    ^This^

    I usually make a jumper with an inline switch so that I can attach the jumper solidly and still turn it on and off for test rides.
    #3
  4. beemerphile

    beemerphile Unreconstructed Southerner Supporter

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    The coils are in series. Only one has a 12v+ lead
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  5. mfp4073

    mfp4073 Long timer

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    hrm. sounds simple and easy. There has to be a catch! But its something I could do this weekend probably. Its been awhile since I have worked on it. I honestly miss her.
    #5
  6. beemerphile

    beemerphile Unreconstructed Southerner Supporter

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    As Steve W. said, the green wire to the battery +.
    #6
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  7. mfp4073

    mfp4073 Long timer

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    I will report back after ive had a chance to test. Hopefully sat
    #7
  8. edmodewey

    edmodewey Been here awhile

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    Have you checked the diaphragms?
    #8
  9. Disston

    Disston ShadeTreeExpert

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    I'm confused. Your OP says the you have already replaced the points but then next up is to replace the timing set. Or is this a reference to the timing chain?

    Hot wiring the ignition is simple enough. A wire from the batt pos to the left coil where you should see a multi colored wire on the outer terminal. Then after that if it proves no improvement replace the points, if you haven't already.

    I always suspect ignition points when a misfire is noted. It has been proven to me that this is usually the problem.
    #9
  10. Warin

    Warin Retired

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    Grounds .. on a points system.

    As above the coil gets its battery +12 v from a green wire. On the other side the ground comes from the points. As the points are bolted to the engine this is where the points find there ground. Not loose is it? Fine. The next bit of grounding for the ignition is the cable running from the rear of the gear box to the battery. A few of these have had bad joints between the cable and the lug, either end. Pulling and pushing on the cable to try and get it to move in the lug may reveal this bad join. The only other place is inside the battery .. bad joints can happen there too.
    That is about it for grounds.
    #10
  11. Warin

    Warin Retired

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    Hey... would you replace yourself at 44? :1drink
    If it is still serviceable, then kept it.
    #11
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  12. mfp4073

    mfp4073 Long timer

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    yes, when the carbs came apart
    #12
  13. mfp4073

    mfp4073 Long timer

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    new in the last 3 years
    #13
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  14. mfp4073

    mfp4073 Long timer

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    points were reset, then replaced. timing set was referring to the chain/gears
    #14
  15. bodine003

    bodine003 Long timer

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    if you have not run a ground from batt - to trans case not frame. and squirt some brake clean and drag a business type card through the points contacts to make sure there is no oily doo-doo in there.
    #15
  16. r60man

    r60man Long timer

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    I had this exact issue on a 1975 R75/6. Turned out is was wiring at the starter relay. Being right under the tank, those connections corrode, badly. When checking them I found that the wire had broken in the insulation. Solder and connector looked fine. All was not. Check all of them.
    #16
  17. Disston

    Disston ShadeTreeExpert

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    That relay, the starter relay, is often a problem due to dirty wire leads. I have never done more to mine than clean the contacts. First time was just remove and replace which makes better contact. But eventually I had to take the wires off enough to spritz them with contact cleaner. Maybe 10 years ago. It has not been a problem since.

    Those battery cables can corrode inside the insulation. Even if the terminals are clean they may have excessive resistance. Peel the insulation back just enough to see if the copper wire is clean. If it is green it probably needs replacement.

    If you gapped the points correctly and they are new they should work. We have had some problems with OEM points not working because the rubbing block was too tall. The brand to get is Norris. They are sold by most suppliers and dealers but sometimes you have to ask for them. It can be tricky to set the gap correctly because the advance unit is in the way and you have to be sure the rubbing block is on the high point of the points cam.

    Points gap too wide or too narrow can cause non running and misfires depending on the extent of how far off they are set.
    #17
  18. UnclePete

    UnclePete Been here awhile Supporter

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    I had replaced a 4 gage battery wire because it was green right at the swaged connector . I clipped off the end ; thought maybe I could clean up the end of the wire and add a new connector to replace a shorter cable in the future .
    The individual strands of copper were green all the way to the center , and all the way to the other end of the cable , under the plastic insulation .
    #18
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  19. mfp4073

    mfp4073 Long timer

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    Ok, did the jumper test and it didnt change anything.

    So list me what that rules out over what ive already tried.
    #19
  20. Beamer Bum

    Beamer Bum Been here awhile

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    If the jumper test was from battery positive to coil, then you have ruled out the ignition switch, kill switch, relay and all plus 12 volt wires/connections. What is left is ground side problem. The coils ground through the points, condenser, points plate, engine, transmission, battery. See post number 12 by Warin. The other option is that electrical problems are really carb problems. :deal
    #20