xsgeoff
XS650 Greenhorn
This will be a bit long-winded, but hopefully if I give a full picture, someone will be able to understand what is up. 
My engine/carbs/airbox are currently 100% stock.
So, I was having issues with (what I at least thought was) fuel starvation when driving at higher speeds for extended periods (>95kph on flat, straight roads). The engine would just lose power and refuse to rev up, and then sometimes it would shudder back to life, and sometimes it would die completely. It would always start up right away again, first kick (or if I still had speed, drop the clutch and bump start). Never any issues in the twisties in the Odenwald hills though, as I would rarely get above 90kph for very long.
Anyways, I cleaned out my petcocks and took apart my carbs. I talked to a guy I know who specializes in old Yami spare parts, and he recommended doing a rebuild, so I gave the carbs to him and they did a full clean/soak and rebuild with all new jets/needles/seals/etc.
I got the carbs back from him in a "bench-tuned" state, so I could drive the bike over to his shop and use his synching tools. After re-fitting the carbs "un-synched", I took it for a quick spin, and it felt like a brand new bike! The throttle was much more responsive and the engine was less vibraty. Our schedules didn't work, so I drove with un-synched carbs for a week and a half or so, just to work each day (less than 4km) and once into the city for about a 15km round trip. Everything seemed to be OK, except one issue was the idle. Some days I would kick the bike over and the idle would be really high, so I'd turn down the screw, and take off for work. Then on the ride home later in the day, the idle would be really low to the point of nearly dying, so I was very often reaching down and adjusting the idle when I was stopped at a light. Figured it was something to do with the carbs not being synched, so I let it be.
Tuesday night, I finally had the carbs synched. Immediately there was a world of difference again. I could reach much higher speeds with less vibration in the engine and all seemed to be great.
But then, on the way home, I experienced my original issue! Cruising along at around 85kph, and the engine started sputting, wouldn't rev up or build power, and died. Pulled off to the side out of traffic, waited a moment, and kicked it straight to life again. So that issue has clearly not been resolved. But wait, there's more! Ever since the synching, the low-end power has been really shitty. At lower RPMs, the engine really sputters and jerks, making for a slightly unstable ride around traffic circles... And I really have to rev the engine up to avoid stalling when I am starting off from stopped, which can't be nice on my clutch.
Sorry for the wall of text, but any ideas?
My completely inexperienced-with-carbs opinion is maybe my pilot jet is too small? That could explain my low-speed issues, but probably not the high-speed issues.
I was going to do a high-speed shut-down to read the plugs and take photos to show here also, to check combustion, but it started storming here after I got home from work. Maybe I can do it tomorrow night after work.
PS. This forum is awesome and has been super helpful so far, and I hope to one day be able to have the knowledge to repay the service and not be so much of a leecher...
My engine/carbs/airbox are currently 100% stock.So, I was having issues with (what I at least thought was) fuel starvation when driving at higher speeds for extended periods (>95kph on flat, straight roads). The engine would just lose power and refuse to rev up, and then sometimes it would shudder back to life, and sometimes it would die completely. It would always start up right away again, first kick (or if I still had speed, drop the clutch and bump start). Never any issues in the twisties in the Odenwald hills though, as I would rarely get above 90kph for very long.
Anyways, I cleaned out my petcocks and took apart my carbs. I talked to a guy I know who specializes in old Yami spare parts, and he recommended doing a rebuild, so I gave the carbs to him and they did a full clean/soak and rebuild with all new jets/needles/seals/etc.
I got the carbs back from him in a "bench-tuned" state, so I could drive the bike over to his shop and use his synching tools. After re-fitting the carbs "un-synched", I took it for a quick spin, and it felt like a brand new bike! The throttle was much more responsive and the engine was less vibraty. Our schedules didn't work, so I drove with un-synched carbs for a week and a half or so, just to work each day (less than 4km) and once into the city for about a 15km round trip. Everything seemed to be OK, except one issue was the idle. Some days I would kick the bike over and the idle would be really high, so I'd turn down the screw, and take off for work. Then on the ride home later in the day, the idle would be really low to the point of nearly dying, so I was very often reaching down and adjusting the idle when I was stopped at a light. Figured it was something to do with the carbs not being synched, so I let it be.
Tuesday night, I finally had the carbs synched. Immediately there was a world of difference again. I could reach much higher speeds with less vibration in the engine and all seemed to be great.
But then, on the way home, I experienced my original issue! Cruising along at around 85kph, and the engine started sputting, wouldn't rev up or build power, and died. Pulled off to the side out of traffic, waited a moment, and kicked it straight to life again. So that issue has clearly not been resolved. But wait, there's more! Ever since the synching, the low-end power has been really shitty. At lower RPMs, the engine really sputters and jerks, making for a slightly unstable ride around traffic circles... And I really have to rev the engine up to avoid stalling when I am starting off from stopped, which can't be nice on my clutch.
Sorry for the wall of text, but any ideas?
My completely inexperienced-with-carbs opinion is maybe my pilot jet is too small? That could explain my low-speed issues, but probably not the high-speed issues.
I was going to do a high-speed shut-down to read the plugs and take photos to show here also, to check combustion, but it started storming here after I got home from work. Maybe I can do it tomorrow night after work.
PS. This forum is awesome and has been super helpful so far, and I hope to one day be able to have the knowledge to repay the service and not be so much of a leecher...
