flyin'chips
Active OPE Member
- Local time
- 11:00 PM
- User ID
- 13341
- Joined
- Jul 29, 2020
- Messages
- 21
- Reaction score
- 18
- Location
- Between piston and cylinder
Hi all,
This is my first post on this great forum. English is not my native language - sorry for all the misspelling and a long post.
I acquired a 1990 262xpg in a bad condition recently. It didn't even try to start. I took it as my first chainsaw project. It has the original KS cylinder and piston.
The saw had water and debris in the gas tank, rust and corrosion inside carburetor and actually turned out it had a wrong carburetor (HDA35). It had several air leaks. Both cylinder and piston have vertical scratches but no real scoring. Ring was very worn. Throttle linkage was slightly bent not giving max throttle. Cylinder has had one muffler bolt thread stripped and repaired but there is some exhaust leak as the heat shield does not seal perfectly to the cylinder. As a bonus it has a sheared flywheel key and some small scrathes on it - probably touched ignition.
The following parts have been exchanged (all parts OEM):
-crank seal (clutch)
-crank seal (flywheel)
-O-ring (flywheel)
-piston ring
-both intake gaskets
-spark plug
-carburetor (brand new HDA120)
-air filter
-fuel filter
-fuel line
Also
-piston has been very lightly sanded where scratced
-cylinder has been lightly sanded (one scratch can just be felt with fingernail)
-flywheel hole has been ground with valve grinding paste
-throttle linkage repaired (no binding)
The situation:
-HOLDS BOTH VACUUM AND PRESSURE 7 psi / 0.5bar at least 5 minutes while turning the crank by hand
-the saw starts, runs and has relatively good power (clearly more than Husky 55 or Stihl ms261)
-accelerates well
-about 3 tanks has been gone through when tuning and testing
The issue:
I'm unable to tune it properly. Will run on factory carb settings (1/1) but I have tried a variety of settings with roughly the same end results. I can tune the WOT rpm easily anywhere (with a tach) but the idle is unstable. I can't find any airleaks. The saw has stopped on it's own maybe one or two times per tank of fuel when on idle.
Max rpm on WOT is now set at about 13500 (factory spec). Idle varies between 2100 and 2800. Sometimes when going WOT it will run on 12800-13000 for about 1-2 seconds and then suddenly rise to 13500. Always when I release the throttle after full rev the rpm drops immediately but it drops too low to 2100-2300 and then slowly rises to 2700-2800 and stays there. If I blip the throttle the idle drops to 2500-2600 (factory spec) and slowly starts to rise to 2700-2800.
Questions:
What are the possible causes for unstable idle and sometimes erratic max rpm?
-improper tuning?
-minor airleak that shows only when hot and running?
-worn piston skirt?
-scrathed cylinder and bad compression when hot?
-misaligned flywheel/ignition?
-problem with flywheel magnet polarity?
-dead av-elements causing excessive vibration and possibly cinching the fuel line?
-bad bearings?
-exhaust leak?
I do not have the means to measure the compression. Also I would not like to throw money and parts blindly at this machine as there is no guarantee it will ever work properly with the old jug.
I'm grateful for any suggestions and help.
-J
This is my first post on this great forum. English is not my native language - sorry for all the misspelling and a long post.
I acquired a 1990 262xpg in a bad condition recently. It didn't even try to start. I took it as my first chainsaw project. It has the original KS cylinder and piston.
The saw had water and debris in the gas tank, rust and corrosion inside carburetor and actually turned out it had a wrong carburetor (HDA35). It had several air leaks. Both cylinder and piston have vertical scratches but no real scoring. Ring was very worn. Throttle linkage was slightly bent not giving max throttle. Cylinder has had one muffler bolt thread stripped and repaired but there is some exhaust leak as the heat shield does not seal perfectly to the cylinder. As a bonus it has a sheared flywheel key and some small scrathes on it - probably touched ignition.
The following parts have been exchanged (all parts OEM):
-crank seal (clutch)
-crank seal (flywheel)
-O-ring (flywheel)
-piston ring
-both intake gaskets
-spark plug
-carburetor (brand new HDA120)
-air filter
-fuel filter
-fuel line
Also
-piston has been very lightly sanded where scratced
-cylinder has been lightly sanded (one scratch can just be felt with fingernail)
-flywheel hole has been ground with valve grinding paste
-throttle linkage repaired (no binding)
The situation:
-HOLDS BOTH VACUUM AND PRESSURE 7 psi / 0.5bar at least 5 minutes while turning the crank by hand
-the saw starts, runs and has relatively good power (clearly more than Husky 55 or Stihl ms261)
-accelerates well
-about 3 tanks has been gone through when tuning and testing
The issue:
I'm unable to tune it properly. Will run on factory carb settings (1/1) but I have tried a variety of settings with roughly the same end results. I can tune the WOT rpm easily anywhere (with a tach) but the idle is unstable. I can't find any airleaks. The saw has stopped on it's own maybe one or two times per tank of fuel when on idle.
Max rpm on WOT is now set at about 13500 (factory spec). Idle varies between 2100 and 2800. Sometimes when going WOT it will run on 12800-13000 for about 1-2 seconds and then suddenly rise to 13500. Always when I release the throttle after full rev the rpm drops immediately but it drops too low to 2100-2300 and then slowly rises to 2700-2800 and stays there. If I blip the throttle the idle drops to 2500-2600 (factory spec) and slowly starts to rise to 2700-2800.
Questions:
What are the possible causes for unstable idle and sometimes erratic max rpm?
-improper tuning?
-minor airleak that shows only when hot and running?
-worn piston skirt?
-scrathed cylinder and bad compression when hot?
-misaligned flywheel/ignition?
-problem with flywheel magnet polarity?
-dead av-elements causing excessive vibration and possibly cinching the fuel line?
-bad bearings?
-exhaust leak?
I do not have the means to measure the compression. Also I would not like to throw money and parts blindly at this machine as there is no guarantee it will ever work properly with the old jug.
I'm grateful for any suggestions and help.
-J