R65LS glitch - Exhaust backfire & cut-out

[Vestibulian]

First thing I'd like to say is, I'm new, so please be gentle.  
Second thing is - I hate seeing "What's wrong with my bike" threads with no information, so this will probably read like an essay.

I bought my first airhead, an '84 R65LS about a week ago from a fella who assured me it would ride daily, himself experiencing no major faults with its operation. I have indeed been riding it daily since then, loving it, but have just recently discovered that it has a tendency to cut out at seemingly random moments (These moments range from pulling up to a stop sign to navigating a corner at 80kph). Not only is this more than a little dangerous, but I'm worried it might be doing permanent damage to the operation of my new treasure.
So I did as any 22 year-old, relatively mechanically incompetent motorcycle owner does in these situations and Googled it. Much to my chagrin, I found a thread posted on another website about this exact problem, by the previous owner of this particular bike.
http://www.advrider.com/forums/showthread.php?t=878965
So I'll be giving him a ring tomorrow to ask for the end of that story. Hard feelings aside for the moment, I'm not completely convinced his diagnosis of it being an electrical problem is correct.
I think I'll be the one trying to fix this either way, so I pose all the information I can think of about the problem to you helpful souls, in convenient dash-points, in the hopes that someone might have experienced something similar:
- Happens more frequently when engine is cold, when fully hot problem doesn't seem to occur. I cannot replicate the problem by riding within any particular RPM range.
- In third gear at about 3500rpm, the exhaust has backfired and bike began to lose power and surge (with throttle held steady) before cutting out completely (OIL & GEN lights illuminated, head & taillights still working)
- Gearing down while approaching stop sign, throttle disengaged, as clutch is disengaged (level pulled) and RPM drops, instead of stopping at idle, just seemed to drop out the bottom of the tachometer, engine failed and would not restart, rolling to a very quiet stop.
- Engine will then turn over but not start. So far, waiting ~10mins seems to allow the bike to restart and run. Quote from PO's thread: "sometimes it will restart after a few minutes and other times will flatten the battery trying to start". Thankfully have not yet experienced this.
[ETA - I have read this can be a symptom of electrical overheating, though if it was, I would expect it to get worse as the engine heats up, and thus be easily replicated by riding with high RPM. Correct me if I'm wrong!]

Is anyone still reading? Thanks.  
So since then I've read an airhead proverb that goes "If you think the problem is in the carburetor, check the electrics; If you think it's the electrics, it's probably the carburetor", and I'm inclined to agree, or at least not commit to one or the other. The previous owner seemed fairly convinced that the problem was electrical - inspecting the coil for cracks (which I intend to do with my own eyes) and installing a new battery -  but the loud backfire in particular suggests to me that it could be a problem with the carburetion.

I've been soaking in suggestions since the problem first appeared while away from home, ensuring the right spark plugs are attached, checking (or just replacing) the ignition coil, checking the mixture and condition of the bike's oil, checking the throttle cable for stress or inconsistency, making sure the carbs are synced...

But it's 12:45, the neighbours are asleep and I've just gotten home from work, so I have yet to even check the spark plugs let alone fire her up. I have the day off tomorrow so I'll be spending the day in the garage methinks. If I could glean any pearls of wisdom from my cadre while looking it over I would be ever so grateful, as I mentioned I am not mechanically minded and am pretty new to the airhead game, but am a quick learner and pretty excited to get my new baby back on her A-game.

Thank you all for your time and attention, hope to hear from any of you soon!  

[Luca]

The only fuel thing I could think to even check would be that the tank is venting, but it sure does sound like an ignition problem.  Carburetor problems are usually pretty consistent and fuel supply problems get worse as revs go up.

Backfires can be caused by the engine missing a spark and letting raw air/fuel mixture into the exhaust, which then explodes when the cylinder(s) starts firing again.  (in old cars some folks used to cut the ignition while driving and turn it back on to get this effect on purpose)

My bosch coil crapped out in a rainstorm.  I got it home, but I had to keep the revs at at least 3k at all times to keep the engine running.  It behaved very much like your bike.  I'm no fan of the "throw parts at it" technique, but a Dyna "brown" coil is a worthwhile improvement even if your Bosch unit is OK, since the Bosch will eventually crack and die at an inconvenient time.  I'd just replace the thing

The ignition control module could also be failing.  I think Snowbum has some testing procedures for it on his site  (www.bmwmotorcycletech.info).  That's the little "black box" under the tank that is bolted to an aluminum heat sink that you're supposed to periodically clean and treat with some fresh heat sink paste.

The only other part of the equation is the advance unit under the front cover, and the wires that connect all of these things together.  Always disconnect the battery before removing/installing the front cover.

My bet is on the coil, though.  Could be that it's drying as it heats up with use.  Wouldn't hurt to check the plugs, but it doesn't sound like it's a tuning issue, again, because it's an intermittent thing.

[Matt Chapter]

First stop is definitely the coil.. Monte will be along in a bit with a picture of his, they crack at the ends.  When mine cracked, every time it rained / got washed (thanks for the wash, Honda of Christiansburg!), it would be terrible to start / would die in flight.

However since there doesn't seem to be water involved, you could indeed be looking at carbs or another electrical problem.

One interesting thing to consider is the behavior of the tachometer during the problem.  If the tach maintains a realistic gauge of the engine speed, I'd lean more towards cleaning the carbs or checking the gas tank vent (it's in the cap).

If however you see the tach drop straight to zero during failure this would indicate an electrical problem.. I'd start by cleaning the battery connections and the chassis ground.

You might also find a shop manual and go through the tune up process, especially taking care to synch the carbs and evaluate the spark plugs.

[Bob_Roller]

This problem comes up every so often .

It usually ends up being an electrical issue .

The last member we had here with this problem, was the Hall Effect sensor in the ignition canister on the front of the engine, commonly called the ' bean can ' .

I had this problem with my '81 R65 17 years ago, at the time, I was told to go through the wiring and disconnect, inspect, clean if necessary, all of the connections in the electrical system .

Never really found the cause for this, found a few pins in the electrical connectors that backed out a bit when the connector was put back together .

Hasn't come back since !!!! 8-)

If you can remember this, the next time it happens, as has been mentioned already, what does the tachometer do when this happens .

In my particular instance, I was doing a lot of night riding and I lost the entire electrical system when this happened .

Sometimes it would come back in a second or two with a nice loud bang from the exhaust, other times I coasted to the shoulder of the road on a dead bike, then in a few minutes it would be normal and start again .

An intermittent electrical problem is one of the most difficult to troubleshoot, don't start ' throwing ' parts at a problem, until you do testing and confirm the part is at fault .

You can waste a lot of money and still not solve the problem .

[jamo]

I had a similar issue with mine tacho to zero then a back fire. I eventually found the problem to be the right hand ht lead had broken in the connection tho the coil fitting that is where it is soldered. Renewed the leads with new Ht cable and my NGK spares from my Jawa. It has run perfectly ever since. I wend down the line of fuel rebuilding both carbs for no reason. Try easy do not get bogged down.

[Tony Smith]

This is a recurring topic, unfortunately the reason it is a recurring thread is that a similar fault can (and usually does) have multiple potential causes.

My process would be as follows:-
 
Carefully inspect all wiring connections to coil, amplifier and bean can. Look especially for chaffed or pinched wires under timing cover. make and break every connector in the chain and give each a spray with contact cleaner. Please do research the correct method of disconnecting the amplifier and beancan JPT (Junior Power Timer - in case you break one and need to buy a new one).

Next, is your coil a "crack-o-matic"? If so replace it on principle, even if it doesn't cure your current problem it will stop an incipient one dead in its tracks.

With tank off and timing cover off, carefully heat amplifier and bean can with heat gun while the engine is running. If engine suddenly stops, replace whichever device you were heating up when it did stop.

Check ignition switch - the R65 switch seems more than usually susceptible to damage from having large numbers of keys hung on it, failure mode can be very subtle. I have replaced two ignition switches on my wife's bike, she insists on carrying a bunch of keys a gaol guard would be proud of. The original switch is now NLA so you, or your auto electrician, will be adapting something else to work.

If none of the above are your problem, or alternatively your testing fails to cause the fault to reveal itself, replace the amplifier and try that, if the fault occurs again, obtain an exchange bean-can (or replace the hall effect device yourself, it isn't rocket science.
 
Of all the above fails - you may have a wiring harness fault.

Electrical faults are not fun (trust me I've had to clear enough of them myself in recent weeks), logic and rigour are your best friends. Particularly as others have already had a red hot go at fixing your bike.


Lastly, you could record (video even) your conversation with the PO, that might be worth selling tickets to watch. :-)

[Vestibulian]

Thanks for the great responses guys  

Definitely no rainwater involved, in down-underverse we've had sunny 25-30c days the last few (so I don't discount humidity). Regarding the tachometer, as far as I can tell it gives a true indication of the speed of the engine, even during failure. I've spent most of the morning looking over it but so far have come up empty. The spark plugs are the correct type of NGK's and don't appear fouled in any way, I had the tank off and inspected the wiring for any breaks or fraying, saw none but dirt so I cleaned all the connections I could get loose.

Having a bit of trouble finding reference photos online. The ignition coil seems to be well mounted into the frame, and is probably going to take some tooling to get out. Is this the factory set up? I only ask because the fuses are in aftermarket houses as well, and it makes for a bit of confusion when referencing the workshop manual I have. I'll be sure the give those connections at the coil a little extra attention as per jamo's advice.

However one thing I did notice after shutting off the bike (after short idle, ~15 seconds) is that the right side exhaust was significantly hotter than the left. I'll let her cool and try again just to be sure, but could this indicate desynchronised carbs?  :-?

ETA: On cold start at idle the bike will commonly sit well below GEN-light RPM range, and the choke doesn't actually seem to fix the problem, rather it exacerbates it, with throttle needing to be applied to keep the bike running. I love my airhead, I hope I can diagnose her sickness soon.  

Cheers Tony! I'll get back to you all as soon as I've run through that little exercise.  

[Bob_Roller]

With the tachometer still indicating correctly during a failure event, I would suggest looking at the coil .

If you still have a black and gray coil, replace it, if it isn't the problem this time, it will be, usually in damp conditions .

It's a known problematic part, I don't know what is available as a replacement part in region of planet earth .

[Tony Smith]

With the tachometer still indicating correctly during a failure event, I would suggest looking at the coil .

Agreed, I didn't pick that up, but tacho indication on an otherwise "dead" engine is "proof of life" as far as amplifier/bean-can goes.

If you still have a black and gray coil, replace it, if it isn't the problem this time, it will be, usually in damp conditions .

Also agree strongly, the crack-o-matic (if still fitted) is simply a failure looking for somewhere to happen.

It's a known problematic part, I don't know what is available as a replacement part in region of planet earth .

The usual "suspects" Moto bins, Boxer works, etc. can quickly dispatch. My R65 wears a mercury outboard coil because I liked the efforts made to waterproof it (and it was cheap from a marine engine wrecker) - if you do decide to go with a non-traditional coil replacement, make sure that its resistance matches the OEM part - Snowbum's site can assist with the values.

[Adrian]

Hi again and thanks for this thread. My bike used to stop for a few seconds every once in a while - maybe every month or so - and then come back alive with a loud bang out the exhaust. Then it would run okay again for a few weeks. The info on here is very useful - although my old girl is still boxed up in a thousand pieces while I wait for a shed to turn up again. My illness doesn't help either.
So well done this has helped me a lot  

[Bob_Roller]

When my OEM black and gray coil failed on me, a little over 20 years ago, my only course, was to get an updated OEM coil, it's red and black .

That coil lasted less than 8 years, started giving me first start of the day hard starting problems below 55 F, 17 C, the primary side of the coil had about .5 ohms .

I would suggest staying away from another OEM coil, especially at a cost of it, if you can do it .