'76 R75/7 restoration

Discussion in 'Airheads' started by Steril, Mar 26, 2021.

  1. korinthias

    korinthias slightly behind the curve…

    Joined:
    Apr 29, 2019
    Oddometer:
    372
    Location:
    Devon, UK
    I bought a bunch of 'raised countersunk slotted machine screws M5 x 12' from a specialist stainless fastener supplier:
    https://www.stainlessmiddleton.co.uk/34298-raised-countersunk-slotted-machine-screws
    They fit my later type 64 bings with the two screw fitting. I notice yours are the earlier style with 4 screws. Not sure if that means a different thread or anything, but I still think it's basically the same screw.

    I actually feel you can get more leverage on a slotted screw in this application, than a Pozidriv head.
    The supplier is UK based, not exactly sure where you are, but their shipping is fast – at least within the UK!
    #61
    Steril likes this.
  2. Steril

    Steril Another Millenial

    Joined:
    Dec 23, 2016
    Oddometer:
    46
    Location:
    Europe
    Thanks, I live in Slovakia now and the local shops carry M5 x 12 so I'll get that.
    #62
  3. Steril

    Steril Another Millenial

    Joined:
    Dec 23, 2016
    Oddometer:
    46
    Location:
    Europe
    I've decided to get new points and timing springs, the motobins package arrived a few days ago - will install it this weekend.
    Wanted to go for a short ride in the neighborhood but the engine was firing just on one cylinder. I'll swap the spark plugs today to see if that's the culprit, if not, I'm going to have another wrenching adventure.
    I've not really ridden the bike yet, just a few km to warm it up for carb setting, but the wrenching is so satisfying I don't really miss riding.

    EDIT: Just went to have a look at the dead cylinder issue, started with the original setup to have a baseline before I swap the spark plugs, and both cylinders are firing. I'll replace the spark plugs, which I didn't do yet because the ones I bought didn't connect to the ignition wires, and hope for the best.
    #63
  4. korinthias

    korinthias slightly behind the curve…

    Joined:
    Apr 29, 2019
    Oddometer:
    372
    Location:
    Devon, UK
    You will reach a point where you suddenly stop and think to yourself “…why am I doing all this? Oh yeah…”
    #64
    Steril likes this.
  5. Steril

    Steril Another Millenial

    Joined:
    Dec 23, 2016
    Oddometer:
    46
    Location:
    Europe
    Friends invited me to join them on a beach - we're landlocked so it's just a flooded quarry.
    It was just 16km (10mi) so I rode my airhead. It starts, goes, breaks and all! The only issue is that it slowly revs up on idle, up to ~2500 rpm. I hope it's the timing springs that I'm going to change anyway. Or it could be caused by the temperature somehow? It's 34°C (93F) here.
    IMG_20210620_122117_2 (1).jpg
    #65
  6. Disston

    Disston ShadeTreeExpert Supporter

    Joined:
    Aug 31, 2009
    Oddometer:
    19,103
    Location:
    Silver Spring, Md
    Sounds like it's a timing issue but not the springs. If you have new springs go ahead and install them. All they do is slow the timing when they work. Old weak springs don't slow the timing enough so you can get pinging.

    What you need is to be able to set the total or maximum timing on the ignition. The static timing is used these days just to get the bike running. Once running we want to make sure the timing advances under acceleration and stops advancing when the rpms reach about 2500 to 3000.

    Are you set up, a traditional timing light that fires off the plugs, so you can set total timing? If this is confusing I or somebody will explain more.
    #66
    Steril likes this.
  7. Steril

    Steril Another Millenial

    Joined:
    Dec 23, 2016
    Oddometer:
    46
    Location:
    Europe
    Thanks @Disston I have the timing light and already did this exercise according to a boxer2valve video, the S mark is exactly in the window and the F is a bit wild, the new springs will hopefully help.
    Dunno about the growing revs, will play with the carb setting as well, pretty sure I'll be able to figure it out eventually. Damn, I love that bike!
    #67
  8. Jim K in PA

    Jim K in PA Long timer Supporter

    Joined:
    Mar 15, 2011
    Oddometer:
    5,761
    Location:
    Pocono Mountains, PA
    More likely to be a carb issue. It's idling on the mains. Drop the idle screws and tweak the mixture screws. Too much throttle opening and too lean an idle mixture will cause a rising idle. If you can't get it to idle properly at ~1000rpm by adjusting the mixture screws, the idle jet and/or passages are plugged.
    #68
    crazydrummerdude, Steril and BJMoose like this.
  9. Steril

    Steril Another Millenial

    Joined:
    Dec 23, 2016
    Oddometer:
    46
    Location:
    Europe
    Thanks for the answer Jim, I've cleaned the carbs 20km ago so it'll probably be the former issue.
    #69
  10. Disston

    Disston ShadeTreeExpert Supporter

    Joined:
    Aug 31, 2009
    Oddometer:
    19,103
    Location:
    Silver Spring, Md
    With a timing light. At idle and until 1300-1500 rpm, or until the advance unit starts to advance timing, the light shines on the S mark. Slowly, with the hand throttle, increase speed of engine. The S mark will be seen to climb in the window and eventually disappear. Around 2500 to 3000 rpm the Dot and the F will appear. They should hold steady in the window and should stay in the center even as rpms are increased above 3000.

    This is the normal operation of ignition timing with the mechanical advance. One thing to be on the watch for with our Airheads is an uneven firing caused by a bent tip of the cam shaft. If the firing is uneven the bike will run poorly. You can usually see this happening if careful enough with your timing light operation. Are you seeing the plugs fire with the S in the window? Or are you seeing an S one firing and a blank portion of the flywheel the next. If you increase rpms slowly does the S seem to jump around and be in two places?

    Be most careful about assessment of the above factors.
    #70
    Steril likes this.
  11. Carott

    Carott Been here awhile

    Joined:
    Jun 17, 2014
    Oddometer:
    115
    Location:
    Saskatoon, Saskatchewan, Canada
    My 1973 R75/5 had a frustrating high idle problem that I chased for months. I bought the bike as a non runner and did a full cleaning and o-ring job on the carbs. After chasing all the usual suspects I found that the barrel of the throttle cable extended slightly past the edge of the throttle lever just enough to catch on the carburetor body at the casting for the idle speed screw. Slightly bending the throttle lever away from the body gave enough clearance for the throttle to close completely.
    This problem was difficult to find because it is almost impossible to see when the carburetors are mounted and I usually disconnect the cables first thing when removing the carburetors.
    Weird issue but that's what happened to me.
    YMMV
    Brett
    #71
    Steril likes this.
  12. Steril

    Steril Another Millenial

    Joined:
    Dec 23, 2016
    Oddometer:
    46
    Location:
    Europe
    The carb setting solved the idle going up issue.
    I have a new work project so not much time to wrench or ride, but the bike is pretty much done now. Except for the larger things that I'll have to outsource such as welding the crack in the oil pan and new paint job.
    There's a funny story about the spark plugs I ordered. They didn't fit my spark plug caps and I was like wtf, well I must have made a mistake. The plugs have been lying around for some time now, and I decided to solve the one cylinder not firing issue. I thought that my leads and caps are non-standard, wanted to order new ones to be able to use standard spark plugs. While shopping for the ignition leads, I stumbled upon this pic
    upload_2021-7-19_14-13-48.png
    I had no idea the large cap can be unscrewed! Did it, my spark plugs fit now so I changed them. Big facepalm.
    upload_2021-7-19_14-14-54.png
    #72
  13. Disston

    Disston ShadeTreeExpert Supporter

    Joined:
    Aug 31, 2009
    Oddometer:
    19,103
    Location:
    Silver Spring, Md
    Some spark plugs have removable screw on tops and some don't, permanent tops. Airheads are one of the rare systems that use the thread of the screw on top for the plug wire.
    #73
    Steril likes this.
  14. sprouty115

    sprouty115 Long timer Supporter

    Joined:
    May 29, 2012
    Oddometer:
    8,717
    Location:
    Providence, RI
    And to make things more confusing, it depends on the plug cap that you order.

    OEM Beru caps ordered from BMW will use the threaded screw to connect.

    But the Euromoto Electric "Beru" caps will us the plugs with the barrel end on the plug.

    BMW-WSR182-3T.jpg
    #74
    Disston and korinthias like this.
  15. Pokie

    Pokie Just plain Pokie.

    Joined:
    Apr 4, 2013
    Oddometer:
    8,367
    Location:
    Fort Collins, CO
    I keep a few of those thread on barrels in my tool box in case I work on something with different plug caps.
    #75
  16. Disston

    Disston ShadeTreeExpert Supporter

    Joined:
    Aug 31, 2009
    Oddometer:
    19,103
    Location:
    Silver Spring, Md
    The threaded screw on caps are great for making shorting rods to balance carbs with.
    #76
    tlub likes this.