Wildguzzi.com
General Category => General Discussion => Topic started by: Canuck750 on June 15, 2021, 06:43:44 PM
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It’s been said here many times that what is perceived as a carburetor issue turns out to be electrical. One of my 1970’s Italian lumps has had an occasional sputter that I notice while cruising along at 30 mph. The bike has new Dellorto carbs and though not perfect the jetting is getting close. I was sorting out a problem ignition switch checking the spark is functioning holding a plug to the head while kicking the bike over and noticed arcing through a high tension boot on a coil, the spark was occasionally taking the path of least resistance jumping to the frame and starving the plug of a spark. The coils hang out front below the gas tank on rubber mounts and when the bike hits a bump the coils jiggle and get close to the frame, spark jumps through a crack in the boot. Had I not had the garage door closed and only a couple lights on I probably would never have noticed this. So I got lucky this time and was able to figure it out.
Check those high tension leads and rubber boots!
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Wow. Lucky find. Fire hazard too.
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If only all electric issues were carb related.
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Here is a couple of other cliches seen around here:
"90% of all Carb issues are Ignition, while 90% of all ignition issues are carburetor."
"Don't mess with the carbs until you are sure its not ignition"
I am slowly learning at cave-man rate of development, to check all the easy stuff first, like watching a motor run in the dark, before doing more involved stuff. I learn best when it breaks, burns or explodes.
Not sure of the absolute truth contained in them, but they are points to ponder.
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I learn best when it breaks, burns or explodes.
That about describes me!
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It’s been said here many times that what is perceived as a carburetor issue turns out to be electrical. One of my 1970’s Italian lumps has had an occasional sputter that I notice while cruising along at 30 mph. The bike has new Dellorto carbs and though not perfect the jetting is getting close. I was sorting out a problem ignition switch checking the spark is functioning holding a plug to the head while kicking the bike over and noticed arcing through a high tension boot on a coil, the spark was occasionally taking the path of least resistance jumping to the frame and starving the plug of a spark. The coils hang out front below the gas tank on rubber mounts and when the bike hits a bump the coils jiggle and get close to the frame, spark jumps through a crack in the boot. Had I not had the garage door closed and only a couple lights on I probably would never have noticed this. So I got lucky this time and was able to figure it out.
Check those high tension leads and rubber boots!
As a general rule, I totally agree with your assessment of carb troubles. Without a good, steady spark, carbs just keep feeding the mixture, but would not be to blame if the cylinder won't burn it.
That said, to this day, it still baffles me why the left carb on my old SP would frost with ice even at idle, producing a super rich mixture and spitting black unburned solid carbon out the exhaust. The ignition was doing its job on this bike.
Many years later, an Eldorado I worked on did the same on the right carb.
I remember replacing all the o-rings in carb cured the issue, but no one on this forum was ever able to come up with the cause or even a plausible theory
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The cracked HT boot to one cylinder turned out to be just half the problem. I still had a intermittent sputter. A friend came over to offer his experience and help. Being a logical fellow he started with removing both HT leads and ran an ohm meter across the ends of each cable while twisting the cables and sure enough the other HT lead had a weak connection to a cap. Twisting the cables while reading the resistance was key.
Replaced the HT cable and so far it’s running real good.
Another simple check I need to use in the future before I strip a carb for the umpteenth time!
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If you can't fix it with a hammer it's electrical :laugh: