FreyZI Posted July 21, 2022 Report Share Posted July 21, 2022 Hoping for some advice on next steps for a '79 G5 that's bucking. Background: This was a project bike and got a full (not museum, but solid) restoration. I did most of the work, but couldn't get it running and so took it to an experienced classic Guzzi mechanic. He got it running (with an entirely new Bender wiring harness and other sensibly replaced electrical bits, etc.). However, his brief rides up and down the neighborhood didn't reveal a problem that has been with the bike ever since. Started out running well, but after 15 minutes or a half hour, it would begin to feel bottled up and decel for a second, followed by a surge, repeated ad naseam, resulting in a bucking sensation. If I parked it and rode the next day, it would start fine and ride fine for a while, but the bucking would eventually return after a bit of riding. I thought this was limited to when the engine was quite warm. At least, until today. A little research and chat with another Guzzi mechanic revealed that this decel/surge issue can be a symptom of ignition coils faltering when hot. I installed new ignition coils and took a spin yesterday -- same issue exactly. Warmed up in the driveway, did ~7 miles and (on interstate doing ~65mph indicated), the familiar bucking returned (though not so bad). After a few more miles, I filled up the tank and continued, doing ~4 miles before going up what passes for a mountain in these parts (somewhat less that 1K') and then another 25 miles or so of country riding, 30-60 mph, with no problem whatsoever. After stopping at a friend's place for an hour, I rode 5 miles or so, with a good bit of bucking in the last mile, to a farmers' market. Bike got a 10-minute rest, then bucked the last 5 miles home. So, the new ignition coils didn't resolve the problem. Today, I replaced the NGK spark plugs with some E3 plugs. That was terrible (worse engine firing and more bucking than before). I removed the plugs and the points were black and wet. I looked at the old plugs -- they were gapped at about 0.5mm. I widened the gap to 0.6mm, per the owner's manual and took it for a ride. Still crap -- probably a bit better than the E3s, but -- until today -- I hadn't experienced the bucking when the engine wasn't particularly warm. Today, both with the new plugs and the re-gapped and cleaned up old plugs, the bucking was present right out of the driveway. Since those rides around the block, I've confirmed that the condensers were replaced in the restoration. I also checked the gaps of the points and they are right at spec of 0.4mm. This certainly seems like an electrical ignition system failure, but I don't have any sense of what may be going on. Nothing has changed since restoration. Bike has been inside. No corrosion. Haven't removed any ground wires. Any ideas would be greatly appreciated. Cheers, Frey Link to comment Share on other sites More sharing options...
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