1982 CB650SC Runs Rich, Deceleration Backfire

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kzinaz
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Joined: Thu Oct 30, 2008 11:48 pm

1982 CB650SC Runs Rich, Deceleration Backfire

Postby kzinaz » Fri Oct 31, 2008 12:06 am

Hello, I have a modified 1982 CB650SC with K&N pod filters and straight pipes. The bike sat for several years before I got it. I cleaned the carbs (Keihin CV) and installed the carburetor repair kits and replaced plugs. It starts perfectly, idles smoothly and actually seems to be running very well at higher rpms as well. To me, it smells like it is running rich though, and my new plugs are starting to look sooty. The original plugs also looked sooty. Also, it backfires on deceleration, although I think it may only be one of the left cylinders backfiring.

1. The pilot screws, are they pilot gas or pilot air? I've tinkered with them a bit, but am close to the manual recommended settings. Is turning in leaner and out richer?

2. The carb repair kit came with 120 jets rather than the original 118, could that have a huge impact? I figured that with the K&N filters one larger jet size might not be inappropriate.

3. Is leaking air into the exhaust a likely cause for backfiring?

Thanks for any help you might have!

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Volker_P
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Re: 1982 CB650SC Runs Rich, Deceleration Backfire

Postby Volker_P » Fri Oct 31, 2008 3:08 am

Welcome here! :D
Pod filters usually ask for larger jets, that's right. However if the plugs look sooty all four after riding at load I won't hesitate to try out the 118's instead. Just keep an eye on your plugs, too rich is no problem however too lean may turn into damage. If you get below 50mpg this is also a sign that you are too rich now (or too fast :lol:).
And yes, exhaust header leaks are a typical origin of backfiring. There should be exhaust seals at the cylinder head.
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cb650
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Re: 1982 CB650SC Runs Rich, Deceleration Backfire

Postby cb650 » Fri Oct 31, 2008 8:43 am

the 81's had 120's and there isnt that much diff in the 81-82. Might be another problem.
Did you clean the tank out?!?!?!?!


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