So ; 90 miles in to a 300 mile day my 1985 R80 does this ;
cough cough , engine dies momentarily, then BIG BACKFIRE !!
Then starts running smooth as usual but it actually felt stronger ???
Guy who was running behind me asks at the first stop, WTH ???
Never had that happen before, and the bike seemed to run better afterwards ??
Ran fine the rest of the day ??
Any ideas ??
Loose wire in the ignition? Cough cough when the circuit went open, then a bang when it reconnected and lit the unburnt fuel in the mufflers?
Try switching your kill switch off and on while riding and see if it sounds familiar.
Good ideas !
I recently replace the old ignition/key switch , maybe left a connector loose !!
I was thinking the same thing.
Now, a "real" backfire is when the engine coughs backwards out through the INTAKE and not the exhaust. There is no such thing as an exhaust "backfire".
A real backfire is most often caused when the ignition timing gets so far off that the spark ignites when an intake valve is still open. The ignited fuel mixture then blows backwards out the intake rather than out the exhaust. Given your description and that the bike ran fine afterwards means it was not a backfire, but instead a delayed combustion, after unburned fuel built up in the exhaust. Finally the conditions were right and "BANG" goes the exhaust.
Woodenshoe to Cheesehead
The fuel and air kept pumping into the cyclinders but the spark stopped sparking. When the ignition started working again there was a lot of fuel in the cylinders and exhaust and it went boom. Definitely ignition. Odd it ran better afterwards, it cleared something out somewhere, maybe a restriction or partial blockage in the exhaust
Don't have a clue yet what caused it , so far i have found nothing amiss
My '85 R80RT was doing that sort of thing one time during each ride. It turned out to be a faulty Hall Effect sensor in the bean can. Same sort of thing others are describing - a momentary interruption in the sparking and a big bang when sparking resumes. In my case, it seemed to be tied to the warm-up cycle.
How old is the heat sink paste on the ignition control module? An overheated control module might also generate a short lapse in the spark dept.
I cleaned and renewed the heat sink paste when i replaced the buggered ignition switch assembly.
I have already replaced the rotor and wonder if the bike is worth all this grief at this point.
I bought it as a supposedly good running model and have had a miriad of niggling little expensive things to deal with in the last year. I knew it would take some fetteling and thought i would enjoy it as a hobby. I don't enjoy mucking about with mysterious intermittent problems as much as I thought i would.
If my finances were better i would just let it go and get something I could reasonably depend on at this point, and i am not sure it would be a Bavarian product.
I am in the drawing for a new bike at the rally in Sedalia, if i win something cool this bike is down the road.
I bet your tankbag sealed off the venting through your gas cap.
Kent Christensen
21482
'12 R1200RT, '02 R1100S, '84 R80G/S
That's a thought , but i recently followed Snowbum's directions and drilled a vent hole in the cap.
Some times i just get so freeking frustrated with this old bike i could scream.
In the case of the exhaust, we use the term "Belch-fire" because that's typically what happens...Originally Posted by ANDYVH
It ran better?Definitely ignition. Odd it ran better
There was no real way to mechanically validate that perception though. I would look for a loose connection at the coils. Check the main grounds. One event doesn't make this an intermittent problem though and that makes if much harder to trace. The momentary loss of power happened while under way which makes me think of a weak connector vibrating due to the road or air motion or a loose, damaged, worn (spark plug) wire. Toss in the "...ran better" and I start to think about dirt/water momentarily blocking a jet in one of the carbs.
I too hate chasing gremlins but that is something we all come to terms with as owners of any machine- eventually. New airhead owners are often driven to lament their decision to purchase the obsolete motorcycle they bought because of the irrational expectation of adding many more pleasurable, trouble free miles to it. Rest assured that the push rod tube seals replaced just 10 years ago on that 27 year old bike and dry at the time of delivery, will need replaced again two months after you buy them along with _eventually_ all the other old parts that make up your 'new' BMW.
Haha...wait until you get a spanking new motosickle full of electronics and repairs that can onlyt be done by the dealer $$$.Some times i just get so freeking frustrated with this old bike i could scream.
I had to replace multiple things over four years but now it runs great again. And by now "I" know all the bolts-and-things I can touch and which I shouldn't
I would do it again. Just to sit on the old Beemer and listen to it purring through the mountains,
Maybe you can get some help from someone who lives in your area? Any airhead clubs nearby?
Btw. your short symptom description sounds like a loose wire (spark plug, coil, can-to-ignition module).
Did it happen again?
/Guenther
I understand the added frustration of a more modern motorcycle and the evil gremlins they carry .
I had a 2005 Triumph Bonneville T100 , it would shut down intermittently and leave me stranded. Took a long time to figure out the "real" problem. A little black box up under the seat on the rear fender
After that it ran fine for 34,000 miles
The BMW only did it one time and has been fine now.
That's what worries me
So far everything i have checked is clean dry & tight.
I will get motivated this next week since it is supposed to rain a lot here and be Africa hot again.
Doug
One time backfire/belchfire/ignition of gas in exhaust system is also often caused when a slug of water goes into cyl and wets the plug(s) for a moment preventing spark for a few revs till engine heat and new fuel/air mix clears things up
With what they sell as gasoline no days that is a distinct possibility.
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