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Classic, Vintage & Veteran For Coventry and Meriden Models. Anything pre-Hinckley goes.

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Old 11-14-2009, 04:23 PM   #1 (permalink)
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66 650 twin misfire trouble

i have a 66 650 that i just got running again after a while heres my story...

when it runs. one cylinder fires and the also gets really hot really fast....the other cylinder dooesnt fire and the carb blows out air....dual amal carbs....it has spark (boyer), cleaned the plugs up they were all black... i have no idea please help

Thanks
pete
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Old 11-14-2009, 06:22 PM   #2 (permalink)
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If the bike has sat for several months, there is a good possibility the gas in the carbs has turned to green varnish stopping up some jets and passageways. Swap sides with the plugs to see it the plug is fouled. How is the compression on the dead cylinder. May have a stuck valve or rings.
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Old 11-14-2009, 06:43 PM   #3 (permalink)
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ok ill go buy a compression tester at harbor frieght what numbers should it read..

i took off the float bowls and checked them seemed fine dont know exactly what to look for but they werent stuck or broken or anything
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Old 11-14-2009, 08:50 PM   #4 (permalink)
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You can do an impromptu compression check with your thumb. pull your spark plugs and press your thumb over the hole as tight as you can. Kick or have some one kick the bike over briskly with the ignition off and the throttle open. You shouldn't be able to hold the pressure back with your thumb. If you can, there is your problem. It doesn't tell how much but does tell if there is some compression. Boyers like a fully charged battery to run correctly. Make sure yours is charged. Since you're running a Boyer, you could swap the plug leads and see if the problem goes to the other side. If it does, check all associated electrical connections. If they are good,and the battery is good, you may have a bad coil.
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Old 11-14-2009, 09:36 PM   #5 (permalink)
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compression on not working cylinder is:
1st kick 30...second 60 ...third 95 where it stays

copmression on working cylinder:
2 kick 30 ...4 or 5th kick 70 where it stays

is that good
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Old 11-14-2009, 10:18 PM   #6 (permalink)
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Check the spark on both cyls you may have a duff coil or lead etc.
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Old 11-15-2009, 01:09 AM   #7 (permalink)
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Did you hold the throttles wide open when you kicked it for a compression test. If not, you didn't get the true reading.
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Old 11-16-2009, 12:16 PM   #8 (permalink)
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Before you go pulling the engine apart, do a thorough maintenance, by the book, front to back, top to bottom, side to side.

The book lists the procedures in a particular order, because each step requires other things be in order BEFORE proceeeding to the next.

(sounds like a simple valve adjustment issue, though...)
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