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Thread: 1985 R80 - Died and Won't Start

  1. #1
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    1985 R80 - Died and Won't Start

    Hi All

    I'm new member that recently acquired my first Beemer a few months ago; I'd been wanting an airhead for quite a while, and I'm loving it so far. Bike in question is a 1985 R80 that had been converted a few owners ago from an RT to a naked bike, and has been well taken care of as far as I can tell. Mileage is currently just over 29.5k, of which I've put a little over 600 so far. Only issues to this point I've had to address are a leaky oil pressure switch, and an idle that would get a little high after the engine got warm (more on that later) that is, until I went for a ride on Sunday. I'll try and be brief as possible and lay out the scenario, and hopefully someone can tell me where I either screwed up or how to remedy the situation (or both).

    I haven't yet done a valve adjustment on the bike (perhaps one area where I screwed up) but I didn't know if the mileage of the bike necessitated one quite just yet. However, I noticed shortly after getting the bike that the idle would climb to a little over 2k, and occasionally just shy of 3k after getting warm. It would even occasionally climb while sitting at stoplights. I ruled out the mechanical timing advance mostly because it wouldn't come unstuck when attempting to "drag" the RPM down with the clutch, and it would still remain high after cutting the engine off and restarting, as well as the fact that it would climb while stopped without any throttle input. Having done that, I focused my attention on adjusting the butterfly plate on the carbs with a friend who isn't an airhead expert by any means, but knows motorcycles pretty well. It was a pretty minor adjustment, and we did it after a good 20+ mile ride while the engine was good and hot, and it got the bike idling right around 1k no problem. After the carb adjustment, we went out for a longer, 40 mile ride where the bike performed well, though on occasion when clutching out for stops, the bike would come close to stalling without ever doing so, and I chalked it up to needing to tweak the throttle cable tension just slightly. With the throttle open and riding along, I noticed no loss of power or stumbling. That was last Sunday.

    I rode the bike during the week, and it cold started fine, but after the carb tweak I needed to keep the enrichener on for a bit longer; before the change I could flip it off after maybe 30 seconds or so in 60-ish degree weather. Afterwards, I noticed it needed a minute or two longer to wake up, but figured this was normal. Idle was still better than it had been, and bike rode just fine, but on Friday I noticed that if I removed ALL throttle input, the idle would drop to below 1k, and die every time. It didn't affect rideability, and if I put just a hair of throttle on, and I mean, like a mm of cable pull, the bike would idle fine at 1k, fat and happy. No stumble, no loss of power. I again figured that this must be a cable tension issue, but when I got back Friday it was dark and cold, and figured I'd get it warm and ride it around on Sunday and make the adjustment then.

    This past Sunday I took the bike out and it again started fine with a little bit of extra enrichener. It was a nice 25 mile ride with no symptoms of poor performance that I could tell, but the bike would still want to die when totally off throttle and the plan was to adjust the throttle cable when I got back home, because it idled fine with barely any twist. Towards the end of my ride I was crusing through a local sleepy downtown not too far from home at around 25 MPH when I noticed what felt like the bike needing to be put on RES. I was a little alarmed, because I had just filled up mid week, and while I had been suspecting that my gas mileage isn't necessarily amazing, I should have had plenty of gas. Before I could put it on RES, the bike died on me, and I coasted to a stop on a side street. I checked the fuel level, and found that I did in fact have gas, and tried to get it fired again, to no avail. It would crank fine, occasionally turn over very briefly and immediately die, and it actually backfired on me a couple of times but it never completely caught. I checked the carb bowls, found them full of gas and free of crud, and after letting the bike cool for a couple of hour thinking it might be ignition related, I found it still wouldn't turn over. I've since loaded the bike in my truck and brought it home.

    I know that a bike with valves set too tight won't turn over, but am I correct in thinking that a degradation in performance would have been noticed long before any sudden engine cutout and subsequent starting issues? I'm also aware that my carb tweak may have exacerbated an underlying issue or be the root cause of my current problem, but I'm a little stuck as to what I should check first, or troubleshoot. Any guidance, wisdom or constructive public shaming is appreciated.

  2. #2
    Liaison 20774's Avatar
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    Welcome to the forum! Thanks for the input...might be a lot of things going on there.

    A couple of things to do before trying to start it again. I would definitely check the valve clearances. Shoot for 0.006" intake and 0.008" exhaust. Probably before doing that, you should be sure of the head bolt torque. It's a somewhat critical thing to do. You have 6 bolts that hold the head down. The torque is no more than 25 ft-lbs. Probably should loosen each bolt/nut one at a time just a bit then retighten to 25 ft-lbs. Then check the clearances. The '85-on models should have had new valve seats with the better metallurgy, so the idea of valve recession or problems is not likely, especially at this low mileage.

    You should renew the heat sink paste on the ICU. It sits on a plate under the tank...I'm not totally sure where...others will probably know. But if the original paste has disappeared, the ICU can get hot and malfunction. The paste helps draw heat to the heat sink.

    With the rising idle RPMs, that's usually indicative of an improper carb setup based upon what you tried with the clutch dragging the idle down. At some point, you should start from scratch and do a full carb synch process. As you have done, warm the engine up and go through the steps. You should have a fan or two blow air across the engine as you idle it and make the settings. The process involves three parts: idle mixture, idle speed, and cable tension. Mixture and speed is an iterative thing...once you set the mixture and speed, then go back and recheck the mixture. The cable tension is typically done at an RPM just off idle say 1500-2000.

    Including your location in your profile would help others to see where you are and to see if there are other Airheads near by. Also, check the Anonymous Book to see if there are other BMW owners around that might be a second set of eyes and hands.

    Start with the valve clearances. Let us know how things go.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

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    Kurt

    Location added, thanks for the tip, as well as the direction. Much appreciated!

  4. #4
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    Yes location is important to get local help. I would suggest a full tune up / adjustment to the bike.
    1) adjust valves.

    2) remove and lube the advance mechanism, inspect springs for proper operation. (i think '85 has a mechanical advance)

    3) adjust carb mixture, sync throttle cables and idle. (fully warmed up, 20 minute ride)

    4)inspect and adjust ignition timing.

    5)re-tweak carb sync if necessary.

    You need to do these things to get a baseline, just going at it in a non logical manner will have you chasing your tail. All of these items interact with one another. Good luck, they're simple bikes if you take a methodical approach. Lots of good info and people around, cheers.

  5. #5
    Registered User Guenther's Avatar
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    Do you get a spark with a simple test putting the spark plug on the cylinder and turn over the motor?

    /Guenther
    2017 F700GS

  6. #6
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    Guenther

    I had heard that on the later, non-points bikes that grounding the plug on the jug can cause serious issues? Or is that only when it's not grounded properly?

  7. #7
    Liaison 20774's Avatar
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    Only when not grounded properly. Think of it this way. When the plug is screwed into the head, the threads are the path to ground for the spark. So, if you simply put the plug into the end of the spark lead, completely ensure that the threads are touching the fins of the engine (I use a small bungee cord), then you still have a path to ground for the spark.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

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    Thanks everyone for the input so far. I haven't yet had a chance to do the valve adjustment, but have been doing a lot of reading up on the process and it seems pretty straightforward. Except: setting end play on the rocker arms. I was planning on doing the c clamp method, but Snowbum seems to recommend against this for the 85+ model year bikes because shims are used. I'm slightly confused by this, but I'm also an extremely visual learner (Snowbum is a wealth of info but I find the lack of photos tough). I understand the concept of shimming to remove play, but I would think the c clamp method could still work, and I've seen info that otherwise confirms. What's the word on what other monoshock folks do, or those who have modded their bikes to the 85+ spec?

  9. #9
    Liaison 20774's Avatar
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    I agree with the assessment of Snowbum's site...lots of great info...pictures would be mo' better...I think he's working on that. Read about the changes in the rocker arms over the years on Anton's site:

    http://largiader.com/tech/rockers/

    I think you'll see why the sideward squeeze doesn't work. On my /7, where the c-clamp might work, I've only just used my fingers to hold the tension on the blocks which I began to tighten the head bolts. I think one can go overboard with this and create some friction where it might be harmful.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  10. #10
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    Quote Originally Posted by shortwaveradio View Post
    Thanks everyone for the input so far. I haven't yet had a chance to do the valve adjustment, but have been doing a lot of reading up on the process and it seems pretty straightforward. Except: setting end play on the rocker arms. I was planning on doing the c clamp method, but Snowbum seems to recommend against this for the 85+ model year bikes because shims are used. I'm slightly confused by this, but I'm also an extremely visual learner (Snowbum is a wealth of info but I find the lack of photos tough). I understand the concept of shimming to remove play, but I would think the c clamp method could still work, and I've seen info that otherwise confirms. What's the word on what other monoshock folks do, or those who have modded their bikes to the 85+ spec?
    Here's some rocker arm info. Easier to follow and succinct. Anton is another great resource for airheads and k bikes. cheers.
    http://www.largiader.com/tech/rockers/

  11. #11
    Registered User 6322's Avatar
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    You may have an air leak between the carb and head. Does it increase rpms evenly or does it run rough as it increases? A simple test would be to spray a little carb cleaner around the intake tubes and note if it affects the idle. At least you could rule that out. Generally if it's a valve issue (clearance going away as it warms up), the idle gets rough but I've never seen it increase idle speed. Good luck with your project.
    Gary Phillips - #6322
    Wildland Firefighter, Retired, Riggins, ID
    Heartland Moto Locos BMW Riders
    '77 R100/7 Dirt Hack, '83 R80ST, '85 K100RS w/EML, '93 K1100LT, '00 R1100RS

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    Update

    Hey All

    As mentioned, thanks for all the suggestions and help so far. As an update, I torqued the head bolts and checked valve lash yesterday; valves felt pretty tight all around, but making the adjustment still didn't solve my non-start issue. I discovered after doing a little more investigating that the plug lead at the coil (Reddish Dyna, 1.5 Ohm) for the right side cylinder had some pretty bad green corrosion built up on it, and inside the coil "port." I cleaned all this up with some vinegar and salt, tested the coil for resistance and confirmed spark while grounding the spark plug threads, but still no-joy on getting the bike to turn over. I will note that the plugs seemed pretty badly fouled and one smelled strongly of un-burned fuel, and I'm hoping that new plugs may result in some better results, having made the other adjustments. As it stands, I'm back to where I was on the side of the road as far as what the bike is doing: it'll crank fine, seems like it wants to catch, backfires occasionally, but can't seem to get all the way there. I'm a little stumped because I seem to have fuel air and spark, but perhaps not consistently or in the right ratios.

    What should I check for next?

  13. #13
    Liaison 20774's Avatar
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    So you're getting spark at the plugs. But is it sparking at the right time? I might have missed where you've determined that it's firing at the S-mark. One way to maybe see if you're in the ballpark is to monitor when the plugs fire relative to the flywheel timing marks. You could take the plugs out and put them into the caps and ground the plugs to the engine fins. Then, turn on the ignition but don't start the bike. Rotate the engine using either 1) allen bolt at the front of the alternator (plugs are out and the engine should turn easily) or 2) put the transmission in 5th gear and use the rear wheel to turn the engine. Do you hear a snap of the plugs when they fire when the S-mark is in the center of the window?
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

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    Kurt

    I have not yet determined that it's sparking at the S mark, and I'll put that next on my list if the new plugs don't solve the issue. What could cause timing to jump or get out of sync so suddenly? Broken tooth on the timing chain sprocket?

  15. #15
    Liaison 20774's Avatar
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    Any number of things that might cause the timing to chain...but probably no need to jump to timing chain issues just yet. I'd just confirm that the timing is more or less correct and go from there. If you find you're way off, then start investigating that.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

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