SteveSr
Addicted to ArboristSite
Hello,
Here is something for your thinking cap... Before that first beer!
There was recently a poster who caused an overheating / partial seizure issue with an 028 AV while he was "noodling" (i.e. bar buried) rounds. This was confirmed with IR temperature measurements and solved by opening up the high-end screw another 1/4-1/2 turn.
I was recently rebuilding an FS-120 with a brand new carb set to the Stihl Specs for that particular carb. With a polycut head it ran fine at these settings but ran into the ignition limiter making it impossible to tune the high-speed screw on the carburetor. To get it off the limiter I removed the blade guard and installed a mowing (line) head with the line set about 2" longer than the cutter on the guard would normally allow.
Under these conditions the trimmer was not on the ignition limiter and sounded pretty normal. Unfortunately, I don't have a tach to measure. The interesting thing is that at WOT the power output and head speed increased rather noticeably when I opened up the H-screw. This would tend to tell me that the engine was running lean before I made the adjustment. In fact, this is how Stihl tells you to set the carb in one of their manuals (I forget where I read it) minus the extra string length.
Both of these cases would tend to indicate that for optimum operation under load the carb should be set richer than the stock unloaded "burble" sound.
This sort of makes sense because at lower RPM the exhaust port is open longer which allows more of the incoming charge to escape before the piston closes the port thereby leaning out the mixture.
So at what RPM below the power band does this effect occur? Was noodling the 028 and longer string on the FS-120 too severe a test?
Would setting the high end richer help with horsepower and saw longevity on the smaller saws? I am not sure it would matter much on the larger saws as it would be much harder to overload them and get them out of the power band.
Your thoughts?
Thanks,
Steve
Here is something for your thinking cap... Before that first beer!
There was recently a poster who caused an overheating / partial seizure issue with an 028 AV while he was "noodling" (i.e. bar buried) rounds. This was confirmed with IR temperature measurements and solved by opening up the high-end screw another 1/4-1/2 turn.
I was recently rebuilding an FS-120 with a brand new carb set to the Stihl Specs for that particular carb. With a polycut head it ran fine at these settings but ran into the ignition limiter making it impossible to tune the high-speed screw on the carburetor. To get it off the limiter I removed the blade guard and installed a mowing (line) head with the line set about 2" longer than the cutter on the guard would normally allow.
Under these conditions the trimmer was not on the ignition limiter and sounded pretty normal. Unfortunately, I don't have a tach to measure. The interesting thing is that at WOT the power output and head speed increased rather noticeably when I opened up the H-screw. This would tend to tell me that the engine was running lean before I made the adjustment. In fact, this is how Stihl tells you to set the carb in one of their manuals (I forget where I read it) minus the extra string length.
Both of these cases would tend to indicate that for optimum operation under load the carb should be set richer than the stock unloaded "burble" sound.
This sort of makes sense because at lower RPM the exhaust port is open longer which allows more of the incoming charge to escape before the piston closes the port thereby leaning out the mixture.
So at what RPM below the power band does this effect occur? Was noodling the 028 and longer string on the FS-120 too severe a test?
Would setting the high end richer help with horsepower and saw longevity on the smaller saws? I am not sure it would matter much on the larger saws as it would be much harder to overload them and get them out of the power band.
Your thoughts?
Thanks,
Steve