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DO a compression test first!!!!
My friend had a similar problem on his 650G Katana which he could not trace the problem.... He eventually bought the bike to me and after doing a compression test that showed lack of compression, I discovered that the inlet and exhaust valves were not sealing at all (2PSI).
Stripped it down and the valves ALLwere shot, one had a small chip in it and I suspect that it went into the piston as it had a very small hole in it about 1mm round, almost like someone had drilled into it.
The thing is that the bike was doing exactly what you said but there was only a minor oil leak (.5 litre a week), the exhaust pipe was stone cold until it had been running for 15-20 minutes, and then it would eventually come up to temperature.
We traced the likely cause of the problem back to a long run he did with a group through the mountains on a very hot summer day on and off the throttle, then when they had stopped for some midday refreshments, almost as soon as he turned the bike off there was a massive storm which I think shock cooled the bike and released the chips from the valves.
A strip and then rebuild and all was fine again! 4 years later and it is still going perfectly!
I also had a similar problem on one of my old CowaSaki 4's and it was actually an ignition coil lead that was broken, and I guess that after the engine heated up enough, the coil lead would make a connection.
If it was a coil or ignition problem then it would do it on 2 cyls because the coil actually fires both plugs at the same time.
As I said, I would check compression first though and go from there!
My friend had a similar problem on his 650G Katana which he could not trace the problem.... He eventually bought the bike to me and after doing a compression test that showed lack of compression, I discovered that the inlet and exhaust valves were not sealing at all (2PSI).
Stripped it down and the valves ALLwere shot, one had a small chip in it and I suspect that it went into the piston as it had a very small hole in it about 1mm round, almost like someone had drilled into it.
The thing is that the bike was doing exactly what you said but there was only a minor oil leak (.5 litre a week), the exhaust pipe was stone cold until it had been running for 15-20 minutes, and then it would eventually come up to temperature.
We traced the likely cause of the problem back to a long run he did with a group through the mountains on a very hot summer day on and off the throttle, then when they had stopped for some midday refreshments, almost as soon as he turned the bike off there was a massive storm which I think shock cooled the bike and released the chips from the valves.
A strip and then rebuild and all was fine again! 4 years later and it is still going perfectly!
I also had a similar problem on one of my old CowaSaki 4's and it was actually an ignition coil lead that was broken, and I guess that after the engine heated up enough, the coil lead would make a connection.
If it was a coil or ignition problem then it would do it on 2 cyls because the coil actually fires both plugs at the same time.
As I said, I would check compression first though and go from there!
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