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dudley472
Member
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Posted: Sat Jul 19th, 2008 08:52 pm |
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| following the sad death of the mag on my 32 sumbeam a rebuild was in order. It cam back and the bike started second kick..........unbelievable !! it used to take at least 20 mins anyhow, the bike runs well and that carb problem i have been chasing since i got the bike has mysteriously disapeared.....all good so far. Problem is when i shut off to change gear i get a huge backfire, it is worse if you retard the ignition but i have put in as much advance as i dare, its just one bang, no farting and popping as the revs go down so i don't think its weak and the plug is a good colour. Any ideas ??
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DM
Member
| Joined: | Tue Jun 12th, 2007 |
| Location: | North Cornwall |
| Posts: | 228 |
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Posted: Sun Jul 20th, 2008 09:00 pm |
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An air leak on the carb, or a worn valve guide (inlet or exhaust) if its open valve gear could cause it to backfire in this way.
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dudley472
Member
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Posted: Sun Jul 20th, 2008 09:19 pm |
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| thanks for that, i found the trouble this afternoon, the exhaust was a bit loose cheers
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the vintagent
Member
| Joined: | Sat Jun 7th, 2008 |
| Location: | San Francisco, California USA |
| Posts: | 14 |
| Favourite Bike: | 1933 Velocette MkIV KTT ... |
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Posted: Thu Aug 21st, 2008 02:24 am |
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If you get a solid backfire when the throttle is rolled off, it's invariably the exhaust system - a leak at some joint (cylinder head to pipe, or pipe/silencer) will introduce a bit of oxygen into the system, which ignites the suddenly fuel-rich exhaust (from unburned fuel). Bang!
pd'o
http://www.thevintagent.blogspot.com
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