Back on an Airhead - 1975 BMW R90/6

Discussion in 'Airheads' started by tete, Aug 27, 2012.

  1. tete

    tete clown shoes

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    I have the Boyer electronic ignition. I may have to wait till Monday to try this balancing. I have family in town. :(

    However I ended up trading fr the /6 tank w knee pads. I wanted to get opinions on wether or not the gap between the seat and the tank seem to big. I don't think it is but I often get picky and paranoid. Feel free to share opinions. I'll have to raise the bars a bit as in the current position thy hit the tank. [​IMG]
    The gap may actually be ok because the freshly coated Tank will gets scratches from the seat if its too close.

    I have a new cover for this seat as well as a grab rail coming. I can't find trim prieces so ill use some generic black trim. I'll pinstripe the tank and fenders myself when I get the first coat up.

    Saw this cat the shop today. Pretty wild. Such a big looking tank and only holds 3.5 gallons. Most of it is for show and the intake system and stuff.
    [​IMG]
  2. tete

    tete clown shoes

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    the more I look at this tank, and the more black BMW's I see the less I want black. The more its keeps telling me to go raw on the tank. with a nice clear coat. the tank is really straight just really ugly paint job. stripped it think it might work. Maybe I'll strip it saturday and see what it looks like. as long as there is no bondo it could be cool . Maybe raw with black pin stripes? is there a way to maybe strip it to raw then have it get a little surface rust and then keep a little rust here and there then clear it? or is rust like the plague and it will destroy it in the long run? even if its very slight and cleared

    Also, under the cap should it have rubber? I'll post pics... . aesthetically I think I have to decide which way to go before i invest a ton of money and decide I don't like it.
  3. disston

    disston ShadeTreeExpert

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    As I mentioned before, We used to balance the carbs by lifting the plug caps. This is not allowed any more and a bike that has any after market electronic ignition can blow the ignition module part of the system by lifting the plug caps. You must use the short 4 mm rods on the spark plugs to short each side out in turn to balance the carbs. These rods should be tightened with a wrench because they will vibrate loose if not tight enough.

    A too low an idle will cause an oil starved engine. It can ruin the lower end of the engine. A too low an idle will ruin your day. I believe the lowest idle in the book is 6 or 7 hundred. These are quit low. Most riders today have idle set around 1000 on the R90s. Mine is a little below 600 I think.

    I'll be back.
  4. tete

    tete clown shoes

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    I went for a little ride today. Just figured it might be nice to run through the gears a bit. Bike ran fine. Steady etc. however I set the idle a little higher before the ride. A couple turns in from zero. I'm not sure if maybe I'm running rich or not but when I went to turn the bike off it wouldn't. It just kept running. Like it was possessed. Maybe I'm running lean? Not sure. I didn't get a chance to balance the carbs yet. As m sure I will take a bit more than 5 minutes for me. Probably an hour or two or three.

    I'm just wondering why it kept running after I hit the kill switch and pulled the keys. Lol.

    I figured the kill switch would end all spark. What gives?
  5. disston

    disston ShadeTreeExpert

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    Tete,

    You should check to see that the flywheel is properly indexed. There is a mark on the flywheel for TDC. The mark on a BMW is usually OT. Take the spark plugs out. Leave the ignition off for this. Stick a wooden dowel into the plug hole and follow the progress of the piston by feeling the dowel rise as the piston rises. Be careful not to break the wooden stick off in the cylinder or other wise cause any damage. But the piston should be at the top of it's travel anytime the OT mark appears in the timing window.

    Do not drive this bike any more until you figure out why this strange behavior. I think the engine ignition may be way off and this could be because the flywheel is not properly indexed.

    If the OT mark on the flywheel corresponds to the piston reaching the top of it's travel then you can recheck the advance and idle timing.

    The symptom you report of the engine not shutting off sounds like the ignition is Way off. This must be solved before it blows up. Do not run the bike if the exhaust pipes are getting Red Hot.
  6. Kai Ju

    Kai Ju Long timer

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    Sounds like you're dieseling, i.e. the mixture is igniting without the benefit of spark.
    Either your timing is way off, or your ignition actually does not shut off when you turn the ignition off, don't see how though.

    You mentioned that you're idle screw is turned in two turns from touching the throttle plate. That's a full turn more than what my Bings are set at. Back those screws off to just one turn from touching the throttle plate.

    Follow disston's advice and verify that OT is OT. A bamboo skewer works well to check the rise of the piston. When you get to TDC, aka OT, you should see that mark in the window.

    [​IMG]

    If you don't, then all your work trying to time the ignition has been for naught.
    If you can't see that mark then somebody installed your flywheel incorrectly and it needs to be corrected.
  7. tete

    tete clown shoes

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    I will address this first thing in the morning. thanks

    here is what I did do in the mean time. while the bike was idling I got of the bike and backed off the idle screws. got it idling pretty low and then used the key and the bike turned off. But when I set idle that low the generator light is on.

    keep in mind the bike starts REALLY REALLY easily. the mixture screw is about 1 full turn out. I figured this is probably a bit rich but since I first leaned it out i'm probably over compensating.

    Thanks
  8. disston

    disston ShadeTreeExpert

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    Leave the mixture screws one turn out. If the carbs are a little rich right now it's fine. The bike will run with the carbs set twice as rich as needed. Too lean will cause problems.

    The bike will idle too slow when just started for maybe 10 minutes. It's this time you have to keep it running with the enrichners or the throttle. We balance to carbs for running when they get warmed up but they won't run the same when still cold.

    Yes, suspect the flywheel is not mounted correctly. Must check. Wooden dowel or bamboo skewer.

    It's also possible the advance unit is not returning to idle and this is causing the engine to race and be too far advanced.

    You need to use the timing light to check advance at 2,500, 3,000 rpm. And verify the timing is going back to idle when the idle comes down. I think you did buy a timing light. But I suspect you have been setting timing with the trouble light at idle since you learned that trick. You have to learn a few more tricks to get this thing right.

    The red light for the charging system will come on at idle. It is normal for the red light to be on when the engine is at idle. It will go off at about 1300 or 1500 rpm. That's normal. It is not a problem for the red light to be on when sitting in traffic. A good battery has enough electricity to run the system for quite awhile with the red light on. And then the battery gets recharged when you raise the rpm.

    The yellow light for oil pressure should not come on at idle. It should never be on if the engine is running. The yellow light should not flicker when at idle.

    From the settings given for the carbs only small adjustments should be made.

    When trying to balance carbs the engine should not be over heated. If the pipes get red hot turn the engine off and let it cool. If you have a big box fan place it in front of the engine when balancing the carbs to prevent this problem.

    I have to go to work now. Good Luck. Just think. only a couple of days ago this thing would not start or run or anything. Now it can go around the block. Progress. :evil
  9. tete

    tete clown shoes

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    Ok it does look to be at TDC so at least we are good there. Must set timing them. Looks to be way off.

    I'll go through the instructions from Boyer once again. Use my timing light and try to get the advance correct.
    Here is where I am at on the stator plate
    [​IMG]
    And after looking at this pic,it lookalike I need to advance it? This oils mean turning the plate counter clockwise I believe. And the making sure at higher rpm that its flashes an F at the timing hole.
  10. tete

    tete clown shoes

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    Here is a pic of my plug
    [​IMG]
    Gapped correctly. I generally tighten them down a hair past hand tightened. I'm wondering if I'm in far enough. To paranoid to find out.
  11. tete

    tete clown shoes

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    Here is what it looks like w the timing light
    [​IMG]
    Just above the mark should I retard it a bit meaning turn the plate clockwise?
  12. tete

    tete clown shoes

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    The bike feels really good. It doesn't feel like its dieseling. It's not getting anywhere near red hot at the exhaust. Seems about right, the way it's running. No back fires, just really smooth powerband. The idles hit low enough for the generator light to flash a bit NO oil light flashing EVER , NONE what so ever. Just feels really good. Idles low. Feels like I could ride it coast to coast.

    BUT when I turn it off it just won't turn off. Neither key or kill. Kinda driving me nuts cause again I feel like the bike is dialed in OK , maybe not spot on but I feel like we are close.

    That being said I have to stall Otto turn it off.

    I read a bit up on dieseling ANSI don't believe this I the case. I checked the spark and we are good there and re-gapped.
  13. Kai Ju

    Kai Ju Long timer

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    Leave your timing light hooked up when you turn the key off.
    If it continues to flash than your ignition switch is not doing it's job and you have your Boyer connected to an always hot lead. Needs to be powered by a switched lead.

    If it does stop flashing you're dieseling, but I'm tempted to say that your Boyer may be hooked up wrong.

    BTW, that plug looks great which reinforces my suspicion that the Boyer is hooked up wrong.
  14. disston

    disston ShadeTreeExpert

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    The plug looks a little lean. You should open the plugs, turn them out, each, another 1/4 turn. They are going to look mostly white because it's the way today's gas burns.But it would be better to have them a little black, then you can turn in a little. Too rich is not as bad as too lean.

    The timing is two degrees too far advanced. Is your picture of the timing window with the rpm raised? If so you should retard timing so the F is not above the arrow. OK, It's 1 degree off. Not bad. If this is at speed, not idle.

    If this is idle you are off by almost 20 degrees.

    You probably need a tachometer so you can know what the rpms are.

    If the pipes are getting red hot when you ride it, something is wrong. The pipes get hot, hot enough to burn but they shouldn't "glow".

    You should try to hook up with another Airhead close to you or even better a Tech Day where there are several experienced gear heads. From here I'm out of ideas.

    The bike didn't have this problem of not turning off before you installed the Boyer? Did it? This is why we want you to fix the OEM system before adding such stuff. It appears the Boyer is hard wired to positive. You turn the rest of the electricity off and on with the key but the coils might be hot all the time.

    With the key off. Take the gas tank off. With the test light grounded at the clip, touch the pointed end to the outer terminal of the right hand coil. If key is off the light should not glow, if it does, the coils are hot.
  15. tete

    tete clown shoes

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    My drawing of the "F" mark was at higher RPMs or at speed. I just took it for a 30 minute ride and it was super smooth overall. The pipes are getting ok hot but certainly not RED hot. About as hot as my hondas. I will make it run a little richer as suggested. I rode over to my buddies house to compare to his R75/5 but he wasn't home. I'll retard the timing in the morning just a hair and put the light to it and see if we are better off.

    I was thinking the same thing about the coils still being hot etc.. maybe I wired something wrong etc.. I'll do as suggested in the morning. I also plan on setting the valves again once the timing is dead on. I'll make a mention on my boyer install thread , perhaps someone else has had this same issue.

    I'm really excited about how well its running.

    I WENT FROM NOT BEING ABLE TO START THIS BIKE - NOW I CAN'T TURN IT OFF? such is life.
  16. tete

    tete clown shoes

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    Great idea.! :deal
  17. tete

    tete clown shoes

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    Ok I did you suggestion and you are right. With the ignition off the timing light still fired.

    I'll have to look and see how I have it wired tomorrow. The timing is very close to being on tho. I went ahead and checked it again Here is about what it looks like.
    [​IMG]
    I just have to get the wiring sorted out and see what's next.
  18. disston

    disston ShadeTreeExpert

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    Well that sounds better. I thought it was still running hot because maybe you never said it wasn't.

    Mysterious thing about the Boyer might be hot. If so it should also power the rest of the bike but maybe not. We're really curious about this particular problem. It's not a common thing with Airheads. I think.

    Kai Ju's idea about the timing light will be easier than my idea about testing at the coils.

    Glad you are finally getting to use the timing light we made you buy. :lol3

    BTW, your R90/6 will blow your buddy's R75/5 away.
  19. disston

    disston ShadeTreeExpert

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    You asked earlier and neither of us answered you, I think. Spark plugs will be fine if tightened just a hair past hand tight. They are not holding anything. They have to only not fall out and even if they did just put them back in. I tighten mine less than 1/8 turn past hand tight.
  20. disston

    disston ShadeTreeExpert

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    It sounds like you have the power feed to the Boyer hooked to something that is hot always. It should be switched, so the Boyer is only hot when the key is on. On my Booster I used the blue/green or green/blue wire that feeds switched current to the coils. This is how it was diagrammed on the instructions. Maybe your instructions aren't as complete or something. On all of these units the blue/green wire will work because it is the hot wire to the coils when you don't have electronic. It is the wire that goes to the outer terminal of the left hand coil.

    The bike is rideable with that much too much advance but I wouldn't leave it there. I've had this myself and eventually got the dot down to where it belongs. It seems just a little happier.

    I currently have to retime my R90 because the points block has worn it seems. Us Booster guys have to do that. You don't have to do that once you get it right, right? But by all means do get it right. :evil