Kubes42
XS650 Member
Hey there, another new guy with more carb questions for those of you who aren't sick of them yet!
Heres the story.
-History
Purchased a 78 xs650 with about 9000 miles that was kept just outside of the D.C. area, and brought it down to Mississippi. Bike is super clean, new gaskets just about everywhere, general tune up, new tires, carbs were cleaned, new spark plugs, updated rear suspension, the list goes on... Previous owner bought it, spent a lot of money for a custom bike shop to make the repairs and light modern mods before realizing he wanted a more modern bike as he didn't know how to do any work himself and didn't want to spend so much money at the shop haha. The previous owner has the receipts, and I also called the shop before buying just to get their opinion on the bike as a 3rd party. They said it was in great shape, only thing left to do was potentially re-jet if you really wanted it to be perfect, but that it ran great . I was anticipating some minor changes to the carbs, as it was last tuned for Washington D.C. winter weather...not exactly 95 degrees with 95% humidity currently here.... So I was sold knowing a little work would have to be done!
-Issue
Got the bike down to hot and humid Mississippi and got her idling, but just barely. Requires choke and prime if it's been sitting cold. Lots of pops from both the exhaust and the carbs. Sometimes pops and sputters itself dead. Sometimes revs itself over 3k and gets stuck there. Also if I rev it, it will sometimes hang at 3k (sign of running lean?). Cannot get a consistent idle RPM to settle to, it goes between those two with no rhyme or reason. Fresh gas. New spark plugs (that are coated pretty black after even short idle sessions...sign of running rich?). Previous owner had the fuel mixture screw turned waayyyy out. like 6-7 turns. Practically falling out haha. I turned it back to about 2, and the headers got red hot within 3-5 min of idle (due to leaning it out?). Backed it back out to about 4 turns and they still seem to run hot, but not red hot in 5 min...
figured ok, well this bike has cheapo air filter pods (new uni ones on the way) and a 2-1 delkevic exhaust on the right side, I should go ahead and re-jet it for the change in airflow and climate, thinking its probably running lean based on the super hot pipes, increased aftermarket air flow, hanging idle, fuel mixture being way open...but kind of confused about the spark plugs showing a rich condition, sometimes bogging down and dying at idle, and climate (hot and humid would mean less dense air compared to DC winter = actually helping run less lean than before?) all showing maybe a rich condition.
I opened up the bs38 carbs expecting to see stock jets. They were as clean as new which was comforting at least. But...rather than stock, there was a pilot of 35, and a main of 155! I was planning on trying a pilot of something like 30/32.5 and main of 140-145...So I was shocked to see jets much larger than what most people are running/recommending (from what i can see anyways, again im pretty new here). I have not been able to get the bike past my driveway since the idle has been so inconsistent, so I cannot speak to how it runs when operating on the mid and upper ranges of the carbs. The 35 pilot jet seems too big, but not crazy. But would running a 155 main jet cause such issues at idle? I know the phases blend together a bit, but seems like I haven't even gotten to run the range where the main would come into play.
I guess my question is, am I just miss diagnosing the lean condition, and its actually super rich? the potential indicators for both conditions is throwing me off a bit. Ive read the carb guide and lots of other posts, and found it super helpful. I still plan on trying my planned jets listed above either way, unless there are some suggestions out there! Please let me know if I have a critical misunderstanding of whats going on, this is my first real attempt at this kind of thing. So far Ive learned a good amount just by reading and watching, but I have a long way to go in real world application.
Thanks for your help!
Heres the story.
-History
Purchased a 78 xs650 with about 9000 miles that was kept just outside of the D.C. area, and brought it down to Mississippi. Bike is super clean, new gaskets just about everywhere, general tune up, new tires, carbs were cleaned, new spark plugs, updated rear suspension, the list goes on... Previous owner bought it, spent a lot of money for a custom bike shop to make the repairs and light modern mods before realizing he wanted a more modern bike as he didn't know how to do any work himself and didn't want to spend so much money at the shop haha. The previous owner has the receipts, and I also called the shop before buying just to get their opinion on the bike as a 3rd party. They said it was in great shape, only thing left to do was potentially re-jet if you really wanted it to be perfect, but that it ran great . I was anticipating some minor changes to the carbs, as it was last tuned for Washington D.C. winter weather...not exactly 95 degrees with 95% humidity currently here.... So I was sold knowing a little work would have to be done!
-Issue
Got the bike down to hot and humid Mississippi and got her idling, but just barely. Requires choke and prime if it's been sitting cold. Lots of pops from both the exhaust and the carbs. Sometimes pops and sputters itself dead. Sometimes revs itself over 3k and gets stuck there. Also if I rev it, it will sometimes hang at 3k (sign of running lean?). Cannot get a consistent idle RPM to settle to, it goes between those two with no rhyme or reason. Fresh gas. New spark plugs (that are coated pretty black after even short idle sessions...sign of running rich?). Previous owner had the fuel mixture screw turned waayyyy out. like 6-7 turns. Practically falling out haha. I turned it back to about 2, and the headers got red hot within 3-5 min of idle (due to leaning it out?). Backed it back out to about 4 turns and they still seem to run hot, but not red hot in 5 min...
figured ok, well this bike has cheapo air filter pods (new uni ones on the way) and a 2-1 delkevic exhaust on the right side, I should go ahead and re-jet it for the change in airflow and climate, thinking its probably running lean based on the super hot pipes, increased aftermarket air flow, hanging idle, fuel mixture being way open...but kind of confused about the spark plugs showing a rich condition, sometimes bogging down and dying at idle, and climate (hot and humid would mean less dense air compared to DC winter = actually helping run less lean than before?) all showing maybe a rich condition.
I opened up the bs38 carbs expecting to see stock jets. They were as clean as new which was comforting at least. But...rather than stock, there was a pilot of 35, and a main of 155! I was planning on trying a pilot of something like 30/32.5 and main of 140-145...So I was shocked to see jets much larger than what most people are running/recommending (from what i can see anyways, again im pretty new here). I have not been able to get the bike past my driveway since the idle has been so inconsistent, so I cannot speak to how it runs when operating on the mid and upper ranges of the carbs. The 35 pilot jet seems too big, but not crazy. But would running a 155 main jet cause such issues at idle? I know the phases blend together a bit, but seems like I haven't even gotten to run the range where the main would come into play.
I guess my question is, am I just miss diagnosing the lean condition, and its actually super rich? the potential indicators for both conditions is throwing me off a bit. Ive read the carb guide and lots of other posts, and found it super helpful. I still plan on trying my planned jets listed above either way, unless there are some suggestions out there! Please let me know if I have a critical misunderstanding of whats going on, this is my first real attempt at this kind of thing. So far Ive learned a good amount just by reading and watching, but I have a long way to go in real world application.
Thanks for your help!
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