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Oh my god !

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TheWrongTrousers View Drop Down
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    Posted: 03 Oct 2019 at 08:19
Took LM1 down to the shops and back, all good until turning the corner into my street and it loses power on right hand cylinder and limps up the road making the loudest back fires on the right hand cylinder i have ever heard in my life. Now when you hear bangs like that in my part of South London you assume the worst if you know what I mean. People taking cover, looking out of shop windows, babies in prams crying - their mothers giving me evil looks as I limp past cringing in embarrassment. 

Engine conks out outside my front door. So I flipped on the right hand choke and it fires up nicely. I took it down the road for a mile or so and back and all is now well. Or so it seems.

So what on earth was that about ?

I imagined great sheets of flame coming back through the open carbs might set the bugger alight. It could happen right ?
Serenity Now !!*!**!!
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Chris950s View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Chris950s Quote  Post ReplyReply Direct Link To This Post Posted: 03 Oct 2019 at 08:31
Are the throttle cables run where they don't snag?
Chris and Karen - Essex
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Death by apathy Quote  Post ReplyReply Direct Link To This Post Posted: 03 Oct 2019 at 09:05
Backfires are often timing related... however you can artificially create a backfire by cutting the spark allowing unburnt fuel to exit the exhaust valve,  then reinstate the spark igniting the unburnt fuel. 
Hackling the kill switch while riding along reproduces thus nicely ..... though not healthy practice.
assuming your backfire is in the exhaust... If it coughs back through the carb you're gonna need asbestos underpants

Anyway all this waffle leads me to suggest checking your spark... everything HT would be my first port of call even a spark plug breaking down could be the culprit... It sounds like it dropped the pot prior to backfiring thereby over fuelling

Worth a look anyway
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 03 Oct 2019 at 09:36
Advance unit sticking on full retard?
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Dave P. View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dave P. Quote  Post ReplyReply Direct Link To This Post Posted: 03 Oct 2019 at 09:44
Intermittent dodgy L/T connection on the offending side ?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote c13pep Quote  Post ReplyReply Direct Link To This Post Posted: 03 Oct 2019 at 10:21
Maybe it`s the `turning the corner` bit that caused the problem ie. chafing wires etc.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote jog53 Quote  Post ReplyReply Direct Link To This Post Posted: 03 Oct 2019 at 16:44
Damaged coil ?  Had similar on my Cali 1100i a while ago. Fired up OK, ran for a while, then onto one pot. Once cooled down would fire OK until it got hot and repeat ad nauseum.....
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 03 Oct 2019 at 16:52
If it's a hot and cold thing, then that is classic coil problem. But they normally cut out, you don't get the back fire.
Brian.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote TheWrongTrousers Quote  Post ReplyReply Direct Link To This Post Posted: 03 Oct 2019 at 18:14
Thanks guys, thats a good load of suggestions. I was wondering about some sort of temporary fuel blockage, a piece of crap in a fuel line or jet that may have cleared itself. Isn't there a saying, electrical problems are usually fuel related and vice versa ? 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote iansoady Quote  Post ReplyReply Direct Link To This Post Posted: 04 Oct 2019 at 10:25
I would be looking at ignition rather than fuel. It sounds as though power has been removed from the coil on the offending side for a short period (or that the lead to the points (does it have points?) had shorted out temporarily as suggested by Chris. Then as described, when power is returned, there's a quantity of unburnt mixture just waiting to be ignited.

It's a little (well tiny) bit like the cough I occasionally get from my V50 when I turn the ignition on then off again without starting the engine. I put this down to a pulse being sent to the ignition amplifier igniting whatever happens to be in one of the cylinders.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote johnno Quote  Post ReplyReply Direct Link To This Post Posted: 04 Oct 2019 at 11:12
Originally posted by TheWrongTrousers TheWrongTrousers wrote:

Thanks guys, thats a good load of suggestions. I was wondering about some sort of temporary fuel blockage, a piece of crap in a fuel line or jet that may have cleared itself. Isn't there a saying, electrical problems are usually fuel related and vice versa ? 
I would keep close to home for awhile and see if it happens again , could well have been something going through the fuel system . I would let the fuel out from fuel bowl also just in case you got dirt floating around.


Edited by johnno - 04 Oct 2019 at 11:15
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TheWrongTrousers View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TheWrongTrousers Quote  Post ReplyReply Direct Link To This Post Posted: 04 Oct 2019 at 15:08
[/QUOTE]
I would keep close to home for awhile and see if it happens again , could well have been something going through the fuel system . I would let the fuel out from fuel bowl also just in case you got dirt floating around.
[/QUOTE]

Well that seemed like a good place to start. A variety of odds and ends in there, some dead insects, various rocks, a fag end, one paper clip, a plastic biro top. one euro coin. That's open carbs for you I guess. (just kidding)  

Amusingly, I found that one main jet was a 140 and the other one a 135. Nice one - previous owner. 

Took tank off, no loose wires that i could see, checked HT leads on nice and snug. Throttle cables all free of snags, no chafing, new electronic ignition fitted so doubt it is that. 

I think I will just stay close to home for a bit and see what happens. 




Edited by TheWrongTrousers - 04 Oct 2019 at 20:25
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jools Quote  Post ReplyReply Direct Link To This Post Posted: 08 Oct 2019 at 09:57
Don't assume anything with electronic ignition! - historically it has been the most unreliable part of the running gear on my old Trident, which is why I now run with the original 3 sets of points.....

The black box was the first thing to malfunction, producing a misfire which got progressively worse. I'd had the system for a couple of years and, to their credit, Boyer Bransden replaced it FOC when I returned it for test, telling me that it shouldn't have failed in the first place. But it failed nevertheless. 

It was also extremely sensitive to voltage. Anything less than 11 volts would cripple the engine, allowing to run at tick-over but no higher. 

I lost interest in electronic ignition altogether when the rotor shed a magnet whilst returning to catch the Dieppe ferry; the entire pick-up assembly was destroyed. Good job I had breakdown cover. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 08 Oct 2019 at 10:01
Originally posted by Jools Jools wrote:

I lost interest in electronic ignition altogether when the rotor shed a magnet whilst returning to catch the Dieppe ferry; the entire pick-up assembly was destroyed. Good job I had breakdown cover. 

That's poor design and mechanical assembly, nothing to do with electronics.
Brian.

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TheWrongTrousers View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TheWrongTrousers Quote  Post ReplyReply Direct Link To This Post Posted: 08 Oct 2019 at 17:26
Yes, but I think Jools is right to says not to rule anything out. I checked all the connections to the Saches box and will probably do so again before I venture out next.
Serenity Now !!*!**!!
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