Post by dieselnut on Feb 25, 2024 18:27:21 GMT -5
Hello all,
This will probably be a long post, so please bear with me. I'll try to give as much info as possible.
What has anyone's experience been tuning the Walbro SDC-1 carbs? I do a lot of mechanical work, so I am quite familar with all of this. That being said, I'm questioning the tuning of the XL-101 that I'm working on. I also don't have any experience with small carbs that have accelerator pumps. I have rebuilt the one on my XL-101 completely, including the accelerator pump diaphragm. I carefully cleaned all of the passages, and pressure tested it during reassembly. I also did a pressure and vacuum test on the engine which tested good, and have roughly 140 p.s.i. of compression cold and 135 hot. I have read the service manual regarding carb adjustments, setting both low and high to 1 turn out, which is about mid-range for the Homelite manual. According to the manual, if there is a lag in acceleration for an accelerator pump equipped carb, there is a problem with the accelerator pump diaphragm or passageways. They are completely clean, though. I understand that those are starting adjustments and tuning will be done from there.
I'd like to add here that prior to replacing the accelerator pump, the saw would idle and run fine with the idle screw at roughly 1 3/4 out and the hi speed at roughly 3/4 out. When tipped forward at idle, though, it would usually die, indicating that the idle was too rich. If I adjusted it so that it wouldn't die when tipped forward, it stumbled badly on acceleration, sometimes dying.
After replacing the accelerator pump diaphragm, it now seems to like about 1 1/2 turns on the idle and 3/4 on the high speed screw and does not seem to load up like it used to, as described above. That is what most of the non-accel carbs tune at, in my experience.
Am I missing anything or overthinking it? When comparing to the manual, it seems a bit off, but is that just the way it is? I'm just trying to reconcile it all in my head.
This will probably be a long post, so please bear with me. I'll try to give as much info as possible.
What has anyone's experience been tuning the Walbro SDC-1 carbs? I do a lot of mechanical work, so I am quite familar with all of this. That being said, I'm questioning the tuning of the XL-101 that I'm working on. I also don't have any experience with small carbs that have accelerator pumps. I have rebuilt the one on my XL-101 completely, including the accelerator pump diaphragm. I carefully cleaned all of the passages, and pressure tested it during reassembly. I also did a pressure and vacuum test on the engine which tested good, and have roughly 140 p.s.i. of compression cold and 135 hot. I have read the service manual regarding carb adjustments, setting both low and high to 1 turn out, which is about mid-range for the Homelite manual. According to the manual, if there is a lag in acceleration for an accelerator pump equipped carb, there is a problem with the accelerator pump diaphragm or passageways. They are completely clean, though. I understand that those are starting adjustments and tuning will be done from there.
I'd like to add here that prior to replacing the accelerator pump, the saw would idle and run fine with the idle screw at roughly 1 3/4 out and the hi speed at roughly 3/4 out. When tipped forward at idle, though, it would usually die, indicating that the idle was too rich. If I adjusted it so that it wouldn't die when tipped forward, it stumbled badly on acceleration, sometimes dying.
After replacing the accelerator pump diaphragm, it now seems to like about 1 1/2 turns on the idle and 3/4 on the high speed screw and does not seem to load up like it used to, as described above. That is what most of the non-accel carbs tune at, in my experience.
Am I missing anything or overthinking it? When comparing to the manual, it seems a bit off, but is that just the way it is? I'm just trying to reconcile it all in my head.