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CG
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« on: June 12, 2020, 08:10:10 AM » |
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Bought non running bike, rebuilt carbs and it was ok it seemed. But over time it started popping, primarily out the left bank but right as well. Then noticed performance degradation. Checked plugs, noticed middle left side plug#4 was blackened but not wet. Knowing the #3 plug runs off same coil, I check it, found the same with it's plug. Replaced the plugs but set them on the engine to see if they were sparking and they were. So I put it back together and ran her hard for about 30 minutes and she seemed perfect. Got back and checked the plugs again and these were also starting to blacken, but not wet. Carbon? Just on those two cylinders. checking compression today on those two but I highly doubt they are the problem give there is only 17k miles on it. At first pass the this would suggest coil to me but again, they are getting spark. Perhaps inconsistent? Thoughts?
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« Last Edit: June 20, 2020, 08:45:54 PM by CG »
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Chrisj CMA
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« Reply #1 on: June 12, 2020, 08:27:48 AM » |
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Each pair of cylinders 1,2. 3,4. 5,6. Share a coil. So if it’s the coil it would necessarily affect both cylinders.
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indybobm
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« Reply #2 on: June 12, 2020, 10:51:43 AM » |
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If the bike has not been de-smogged, then carbs 3&4 also share a vacuum line to the Secondary Air Pump Valve through a tee.
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So many roads, so little time
VRCC # 5258
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CoreyP
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« Reply #3 on: June 12, 2020, 11:51:43 PM » |
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You're just running rich. Sounds like an air problem as in air is not getting to those cylinders. Bad coil could be it but I doubt that. What do the cylinders share in common, then check that. That's where the problem is if I have to guess.
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CG
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« Reply #4 on: June 13, 2020, 07:31:22 PM » |
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Given plugs 3 and 4 run black real quick and they have a coil in common, I changed the coil, reassembled and test drove. Ran great. Got back, pulled the plugs and they were both dry and black..... So I pulled the carbs, that were recently rebuilt over the winter. They look fine as well. I have another set I rebuilt and will put them in but I'm expecting the same result...... I don't believe it's the ECU but I wonder if that coil pack is grounding properly which leads me to suspect my wiring harness???????
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Chrisj CMA
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« Reply #5 on: June 13, 2020, 07:42:59 PM » |
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Do you still have the vacuum lines on 3&4? Cracked vacuum lines can be hard to spot and have been known to cause popping
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CG
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« Reply #6 on: June 13, 2020, 08:08:04 PM » |
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thank you,,,,,,,,,,,,,Yes they are still on, replaced when I rebuilt carbs with silicone lines. 17k miles on the 99 interestate and it hasn't been smogged.....................YET...........
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CG
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« Reply #7 on: June 13, 2020, 08:10:11 PM » |
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Also, ran a compression test and they were all virtually the same.......... I wondered about a spent valve...
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CG
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« Reply #8 on: June 19, 2020, 02:14:38 PM » |
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Recall plugs 3 and 4 were carboned up, black, and it doesn't take long. 3 & 4 have a pair valve and coil in common. Changed the coil, no affect. Desmogged and the problem persists. Went through the carbs again( Pilot screw was at these settings across all carbs: 1.5, 2, 2 1/4, rotations out and no change.
Having said that, the bike no longer pops and actually idles quite nicely. I need to sync the carbs yet but it seems to run ok but a bit lazy. But plug 3 and 4 still carboned up and quick. Compression virtually identical across all cyls. Bike has 17k miles.
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