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2 posts
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I just got a 1979 cb750 10th anniversary. So far Ive had the carbs cleaned and changed the oil. Carbs seem a lot smoother. I found some fine metal shavings in the oil filter. The bikes running but the rpms are jumpy, its backfiring, and the #4 cylinder isnt firing, the pipe isnt getting anywhere near as hot as the others. After it runs for a while it starts to run a little smoother. This is my first bike and any help would be greatly be appreciated.
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125 posts
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I would start by doing a compression test. Check that you have a good, strong spark at the end of the plug connector and a good spark plug. If that all checks out good go for the carburators.
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106 posts
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just what cbrider said, but also compair the spark to the other plugs. with the plug removed try and start the bike and check the spark 1 at a time. it could be a bad cdi
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2 posts
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The spark seems strong. It seems like the #1 and #4 run when I first start then 1-3 run after its warm. When Im driving at lower rpms it runs on all 4. If I try to accelerate quickly the #4 cuts off, I think its the only one, and itll die if I let the rpms down. After that it gets hard to start. I was thinking the carbs need to be synced. I had the crbs cleaned and they told me it was gunked up, looked like it wasnt cleaned in years. I checked the jets on #4 and they seemed fairly clean and they werent clogged at all.
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May 01, 2009; 5:04pm
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