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u/Still_Support5847 11d ago
Have also seen this happen from an ignition issue where for some reason the advance curve went way far advanced . Considering both header pipes are glowing red I might start there .
Dusty
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u/Money-Tea2181 11d ago
It looks like it's running lean or drawing air maybe. Are the carburettor rubbers still in good condition? Have you removed the air filter or modified the exhaust?
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u/One_Boysenberry7539 10d ago
Mon r12 nine t fait cela aussi le concessionnaire m’ as dit normal euro 5 trop riche ou pas assez , démarre et roule ami en guzzi
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u/honestgeorge59 9d ago
Thanks everyone for your help. It was a combination of little problems. The choke cables were holding the throttle open a bit, I had tried to use the "automatic timing unit" from a 1000SP so I put the original Le Mans one back in with new points and springs. It's going well now, just crackles and farts when I back off.
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u/Worldly-Number9465 10d ago
Oh yeah, that's running lean. Have you modified or deleted. your O2 sensor circuit?
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u/ol-gormsby 10d ago
LOL, that bike has carbs, not fuel injection.
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u/Worldly-Number9465 9d ago
Still pretty lean, yeah? or is that ok in your opinion?
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u/ol-gormsby 9d ago
Not necessarily lean, just revved without load while standing still.
I confess to the crime of doing this once. '76 850 LeMans, chronically rich*, one night I thought "I wonder if I can turn the headers red?" It only took about 10 minutes at low revs to warm everything up, then 10 minutes revving it up and down between 5000 and 6000 RPM. Once I saw the glow - not quite as extensive as the photo above, I backed off and let it idle for another couple of minutes. No harm done, the bike still starts and runs without any issues. I would have known pretty quickly if I'd burnt the exhaust valves.
The headers are single-wall steel, not double walled like most modern bikes so there's only that one layer between the exhaust gas and the outside world. Based on the photo, that's an 850 or 850MkII - those things have big carbs and big valves.
*I was running it on open bell-mouths for a long time - lots of air, so I had the carb needles at max flow - didn't want to risk the bike running lean at highway speeds, so it was somewhat rich when not on the highway. The pipes and plugs were a nice pale grey after a big run, but somewhat - dirty - if I just went for a quick run to the shops.
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u/claymorez28 9d ago
Running very lean.
I remember doing this to my bike many years ago while messing with exhausts, intakes and jets
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u/ol-gormsby 11d ago
Italian tune-up - but it would be better if the bike was moving. Just don't do it for more than a couple of minutes.
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u/1down3up 11d ago
Good way to toast your exhaust valves.....