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Thread: Bike Stalls After Freeway Run, Does Not Want to Restart

  1. #1
    MonoRT MonoRT's Avatar
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    Bike Stalls After Freeway Run, Does Not Want to Restart

    I am the original owner of this 1985 R80RT. When I was a new BMW owner, the bike would often stall on freeway offramps after a long freeway-speed speed run. I would shut the throttle down to idle as I approached the stop at the bottom of the ramp and the RPMs would drop through idle and just keep dropping. Back then, the bike would instantly restart and I learned to roll the throttle down, close to idle, but not quite to keep it from stalling as I came off the freeway.

    Today, after a very hot ride on the 405 freeway to work (SoCal is on fire - literally!), I rolled the throttle down to idle as I entered a very congested offramp and the engine stalled. It took a number or attempts to restart. As I got off the ramp and onto the street, I had to stop for a light and the engine stalled again, dropping through idle to a dead stop. This time I had to push the bike off the street and take a quick look as I could not crank it back to life - plenty of cranking power via the battery and starter, but the engine did not want to fire up.

    I have external, clear filters and I could see that they were full of fuel. As I considered what to do next, the bike had a few minutes to sit. I tried the starter again and with some cranking, the engine fired but seemed reluctant to idle. I used my throttle lock to pin the idle at 1,100 RPM, put my gear back on and rode the remaining half mile to work with no more trouble.

    I'll want to give the bike a quick once-over when I get home - providing I don't have to do it on the side of the road before I get home. Suggestions as to what to look for? Or, how to best trouble-shoot if I get stuck?

    Plug wires are of indeterminate age - it has been a number of years since I replaced them.
    Coil is a Dyna - I got tired of the crack-o-matic stock coils.
    32mm Bing CV carbs. Been awhile since I last checked them or cleaned the jet stack.
    Plugs are standard Bosch - I did not get far enough today to see if they were sparking when I could only crank the bike.
    I have the Rick Jones/Emerald Island Alpha ignition with the new-style ignition module with the riveted-on heat sink - maybe a year and a half on that setup.

  2. #2
    Sir Darby Darryl Cainey's Avatar
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    When was the last time you checked your valve clearance?
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  3. #3
    #4869 DennisDarrow's Avatar
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    Quote Originally Posted by Darryl Cainey View Post
    When was the last time you checked your valve clearance?
    Goooood thought.......Start there and then your spark..........Good luck.....God bless........Dennis

  4. #4
    Superkraut typ181r90's Avatar
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    Something else to consider. A few months back I went on a day trip that totaled about 300 miles or so. There was plenty of stopping in between, but on the way home my bike did the same thing as yours, it'd be fine on the highway, then I got off and slowed to a stop sign in local traffic and the bike died, restarted it fine, rode a couple more miles to another stop sign, bike died again. I was still able to restart it, got it home, and when I slowed in my driveway it died again. I should add that all the idiot lights on the bike still worked. Flummoxed, I began checking over all the basics and found that I could turn the ground at the transmission by hand. The bolt that secures the ground cable was in the trans, but alas the threads were stripped. I have no idea how long it was like this - maybe for a few years (I think that was the last time I had to disconnect that cable, at that part of the bike anyway), but for some reason it was making ground at a standstill (since I was able to restart) and while at riding speeds, just not when I was coming back down to idle. I relocated the grounding position to the subframe and all was well.
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  5. #5
    MonoRT MonoRT's Avatar
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    Still at work. Ground cable is clean and tight.
    Valves. Good point. Had a left side cylinder stud repaired a couple of thousand miles back and forgot to re-torque the studs and re-set the valves after the first couple hundred miles. Loose valves would just be noisy. Tight valves won't make good seals. Would that be enough to make the bike hard to start and idle when hot?

  6. #6
    Administrator 20774's Avatar
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    Quote Originally Posted by MonoRT View Post
    Tight valves won't make good seals. Would that be enough to make the bike hard to start and idle when hot?
    That is what I've heard...poor idle might be a symptom of tight valves.
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  7. #7
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    Quote Originally Posted by 20774 View Post
    That is what I've heard...poor idle might be a symptom of tight valves.
    That was the case with my old R500/2. When adjusted to factory specs, would not idle well, and would stall, and then not re-start when hot, especially on very hot 80 Deg.+ days!

    I decided to back out the valve settings to .002 looser than spec, and that totally solved the problem!

    I would rather have them a tad loose than a tad tight - especially the exhaust as that is the one that expands more from the extra heat.
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  8. #8
    MonoRT MonoRT's Avatar
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    Yesterday evening I re-torqued the head that had the recent stud repair and the reset the valves on both sides. They were a bit tighter than spec, but not bad. I also made a really quick run through the carbs, dropped the float bowls and jets, shot carb cleaner through all of the holes I could get at etc...

    Checked plug gaps and did the "end-to-end" resistance check through the two sparkplug wires as mantioned by Mat Parkhouse recently. Got infinite resistance. Not good, but the resistance readings on my DMM have been a bit dodgy recently. Fired the bike up and rode it around a while, checking to see if it would still idle. No problems. Went to bed.

    This AM, buzzing down the 405 carpool lane, the engine died - no sputtering or stumbling - just like the kill switch had been used.

    At the side of the road, while waiting for the AMA roadside assistance flatbed to show up, I pulled a plug and put it into the plug wire. Switched on the ignition and with the plug threads held firmly against the cylinder, I flipped the kill switch on and off. I should get a spark that way. No spark. Gave a quick crank with the starter while holding the plug against the cylinder. No sparks.

    After getting the bike back home, I checked to see if it would start while cool. No. Checked for sparks again. No sparks. Swiped a cage from my younger daughter (it IS my car after all) and came to work so that I could share my sad story.

    So... probably not a valve clearance or carburation issue. Yesterday's incident was just the wake-up call. I need to figure out the best set of steps to trouble-shoot the ignition. Plug wires and coil will be top of the list, but both plug wires at once? In the past, I've just has lots of poor running - especially at low rpms when I had coil or wire problems.

  9. #9
    Registered User lmo1131's Avatar
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    Both plugs at the same time ... maybe faulty kill switch or the ignition control unit (or it's ground wire)? Possibly the black wire from the ICU to the coils?

    Here's the diagram for '83-'84 RT, probably close.

    http://www.stephenbottcher.net/BMW/w...lor_wiring.pdf
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  10. #10
    R100GS, '89 Guenther's Avatar
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    If you don't get a spark on both plugs the problem is more "upstream". Since you have the coil replaced I give it close to no chance to be the cause of the problem.

    I would check for a loose connector at the ignition unit. Ditto the connector between the ignition unit and the "can". If both connectors are firmly plugged in I would call Rick Jones.

    /Guenther

  11. #11
    B Reams brook.reams's Avatar
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    Hall Sensor?

    MonoRT, one more thought ...

    I think this model has a hall sensor that triggers the ignition. They do fail. When heading toward complete failure, then can fail intermittently with heat and moisture particularly if insulation is cracked a bit from age.

    Although written for oil-heads, this does provide some useful information.
    http://advwisdom.hogranch.com/Wisdom...ll_sensors.pdf


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  12. #12
    R100GS, '89 Guenther's Avatar
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    Brook,

    monoRT mentioned "I have the Rick Jones/Emerald Island Alpha ignition " which - as far as I know - includes a new trigger unit (aka "can").

    But you may point to one possible cause of the problem ... no pulse from the trigger unit.

    /Guenther

  13. #13
    MonoRT MonoRT's Avatar
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    Problem Identified

    Just had a chance to tear into the bike yesterday evening.
    I had wondered about a hall sensor. My new Alpha can still contains one and I can't imagine that it's any more reliable than the ones used in the Bosch can. And, I have had a couple of sensor failures in the past that were very disconcerting and intermittent. I bought the Alpha can partially because it appears as if hall sensor replacement will be simpler - plus no mechanical advance to wear out.

    I opened the front cover first and saw that the plug between the bean can and the IM was not tightly in place - the bean can plug had not engaged the wire bail in the IM plug. I thought that I'd found the problem, but after taking care of that, I still had no spark.

    I pulled the tank and had a look at the coil wiring. The primary wires were getting 12 volts with the ignition on and the kill switch would shut that off and on. So, good input voltage and the kill switch is still switching. Resistance over the primary winding was 1.5 ohms and each sparkplug wire came in at 5K ohms.

    Seeing good ohm readings off a meter that I had been complaining about earlier remined me that I had been unable to get any continuity when I checked plug wire to plug wire through the coil. Sure enough, the secondary coil windings read open.

    Well... that explains the poor idle, difficult starting and the final dead stop.

    I do not want to give the impression that dyna coils are unreliable. I posted a couple of years back about how what sounded like a failing conrod shell turned out to be a loosely mounted (by me - should have used nyloks) Dyna coil that was loudly banging in it's frame mount at lower rpms as it powered up and down - working as an electromagnet. This is the same coil that just failed. The fact it did not fail earlier from the abuse it got when it was banging and vibrating in the frame is a testament to the robustness of these coils.

    My Alpha ignition uses the "heavy-duty" IM unit, so I've got a .7 ohm blue Dyna coil on the way now.

  14. #14
    #4869 DennisDarrow's Avatar
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    So didja get it started..............???????????????

  15. #15
    MonoRT MonoRT's Avatar
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    I hope that there will be an "It Started!" post once I get a new coil. In theory, the new coil will be delivered Saturday. I gave the previous Bosch crack-o-matic (complete with crack) to a guy who recycles copper, so I can't do any testing until I've got another coil.

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