Okay, so I'm pretty stumped and could use some help.
I've got a '73 Honda CB350F with about 12k miles on it. I bought it about 2 years ago smoking with the intention of fixing it and selling it. The guy I bought it from was a local, not very well-regarded mechanic and said it was the rings. It was smoking like mad, so it sounded about right (white smoke). I was stupid, though, and didn't do a leak-down or compression test, just went straight to replacing the rings. I replaced them and the valves under the supervision of a mechanic who had a program set up with the community college I was going to and another mechanic I knew who works with vintage bikes. I didn't initially intend to replace the valves but there was a shop move/reorganization while I was working on the bike and the valves eventually got lost, replaced, then found... I fired her up and actually everything was pretty good. Took a while to get the carbs tuned so she would idle, but I actually rode her around a bit and took her to a bike night and everything was good. Started on the first or second kick and everything.
Then there was something wrong with the charging system (turned out it was the stator) and that took me a while to fix, but I did and it charges fine now, but the smoke came back. Not too bad at first, it mostly wouldn't idle and was smoking a little, but it got progressively worse.
Eventually, I gave in and took it to a mechanic near by who's really good with old bikes (I think I've even seen some of his builds on here) and had him check it out. He said the timing was way off and the valves had been adjusted a little tight (I had put them to factory spec, but they seated in a little and apparently factory spec is a little on the tight side in the first place). After he fixed those two things, he said he ran it for a good 15 minutes and rode it around a little and the smoking stopped (he thought there was probably some pooled up in the exhaust that had to burn off first). I picked it up the next day and it already smoked just a little for about a minute at start up. After a while it went away, but when I rode it back to my house, it would give out a puff every time I quickly opened the throttle. A week later when I rode it again (I'm actually living in a different city than the bike resides in) it smoked all through the rev ranges until it ran out of gas. The mechanic who I took it to most recently checked the compression and said that was even a little higher than average, and he filled the oil, so don't worry about that. When I replaced the valves, I did lap them in, and when I found the old valves I looked at them and they don't have any major scarring or wear. I didn't line the gaps in the rings up when I replaced them, but actually tried to put them 120 degrees apart each. The smoking seems to be related to time spent sitting, cause right after I fixed it the first time, I rode it every day and didn't see any smoke.
Any ideas would be greatly appreciated. Sorry for the long post.
I've got a '73 Honda CB350F with about 12k miles on it. I bought it about 2 years ago smoking with the intention of fixing it and selling it. The guy I bought it from was a local, not very well-regarded mechanic and said it was the rings. It was smoking like mad, so it sounded about right (white smoke). I was stupid, though, and didn't do a leak-down or compression test, just went straight to replacing the rings. I replaced them and the valves under the supervision of a mechanic who had a program set up with the community college I was going to and another mechanic I knew who works with vintage bikes. I didn't initially intend to replace the valves but there was a shop move/reorganization while I was working on the bike and the valves eventually got lost, replaced, then found... I fired her up and actually everything was pretty good. Took a while to get the carbs tuned so she would idle, but I actually rode her around a bit and took her to a bike night and everything was good. Started on the first or second kick and everything.
Then there was something wrong with the charging system (turned out it was the stator) and that took me a while to fix, but I did and it charges fine now, but the smoke came back. Not too bad at first, it mostly wouldn't idle and was smoking a little, but it got progressively worse.
Eventually, I gave in and took it to a mechanic near by who's really good with old bikes (I think I've even seen some of his builds on here) and had him check it out. He said the timing was way off and the valves had been adjusted a little tight (I had put them to factory spec, but they seated in a little and apparently factory spec is a little on the tight side in the first place). After he fixed those two things, he said he ran it for a good 15 minutes and rode it around a little and the smoking stopped (he thought there was probably some pooled up in the exhaust that had to burn off first). I picked it up the next day and it already smoked just a little for about a minute at start up. After a while it went away, but when I rode it back to my house, it would give out a puff every time I quickly opened the throttle. A week later when I rode it again (I'm actually living in a different city than the bike resides in) it smoked all through the rev ranges until it ran out of gas. The mechanic who I took it to most recently checked the compression and said that was even a little higher than average, and he filled the oil, so don't worry about that. When I replaced the valves, I did lap them in, and when I found the old valves I looked at them and they don't have any major scarring or wear. I didn't line the gaps in the rings up when I replaced them, but actually tried to put them 120 degrees apart each. The smoking seems to be related to time spent sitting, cause right after I fixed it the first time, I rode it every day and didn't see any smoke.
Any ideas would be greatly appreciated. Sorry for the long post.
