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Old 03-16-2011, 01:46 PM   #1
slick_tire
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Help!!- Is this backfire electrical or a carb issue

Hello all, just joined today and thought I'd jump in with a technical question.

I have an old hondamatic that I'm fixing up and have had it running great only once. All other times it is hunting and backfires through the carb while sitting at idle. I'm suspecting an air leak but also notice that each time it backfires (which is every few seconds) the lights dim really low. Is this normal for a backfire? I know the backfire is slowing the stators rpms but it just seems drammatic considering Honda's rpms are around 1200 at idle. The backfire isn't just a small pop like I would expect, it's like the bike momentarily stops each time it backfires.

I have already pulled the carbs apart and cleaned them 3 times, adjusted the valves, sprayed wd-40 around the intake, leakdown test, new copper gaskets on the exhaust headers, new coil, new cdi, new iridium plugs, new wires and resistor caps, new gas and inline filter - everything people recommend in posts for this type of problem. I just want to rule out something electrical before tearing the head apart to clean the valves. It looks like at one point the rotor magnets were grazing the pickup coil but I tried adjusting the gap as far as I can but it still looks close and the backfire still exists.

Last edited by slick_tire; 03-16-2011 at 01:47 PM. Reason: title not specific enough
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Old 03-16-2011, 02:27 PM   #2
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I'm leaning towards an ignition / electrical issue.
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Old 03-17-2011, 11:53 AM   #3
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The way the bike momentarily stops makes me lean toward electrical also. I guess I could also have an air leak confusing the electrical issue. Any idea what affect the magnet touching the pickup coil has on the bike. Would it just stall completely or keep running?
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Old 03-17-2011, 11:58 AM   #4
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I should also mention the battery is new and I've also tried swapping the voltage rectifier to no avail. The one time that it mysteriously ran well was when I put in the new iridium plugs but I think it might have been coincidence. Fired it up the next day and the problem was back.
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Old 03-21-2011, 04:56 PM   #5
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Really?? No one else??
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Old 03-21-2011, 05:01 PM   #6
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That's a very difficult one to try to diagnose over the web.
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Old 03-22-2011, 08:35 AM   #7
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i have a ninja with carb and it back fires bc fuel is rich...do the PAIR remove and it helps a lot.
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Old 03-22-2011, 09:12 AM   #8
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You didn't specify which Hondamatic you have, but have you been to http://forums.sohc4.net ? That's where I used to hang out when I had 72 CB750.
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