I have a Dolmar PS-420 I have had for a couple of years. It used to run O.K. Then it didn't. I have not been able to fix it and it has me stumped, to the point this is getting personal between me and that saw.
Symptoms:
Pull Pull Pull, no start.
Pull Pull, run smooth for 3 seconds, then stop as if the run switch were turned off.
Compression:
I have not checked compression, but saw pull cord seems to have as much resistance as several of my other saws, especially for a 42 cc saw.
Compression seems good to me.
Saw falls very slowly when held by the handle, almost holds itself up.
I sealed off the exhaust and intake, without carb installed, and saw held 10 psi pressure and 10 in Hg vacuum for several minutes. I conducted test with a Mighty Vac through the spark plug hole.
What I have done to try to get her to run:
Vac Test
Pressure Test
Used coil from a 421 (maybe not right?)
Swapped plugs... resistor/non-resistor plugs
Carb Kit, and I checked and re-checked installation of parts
Sprayed carb inside and out, removed high/low jet screws and sprayed through all, did remove a bit of gunk from the high jet.
All new fuel lines
Checked and re-checked installation of purge bulb lines vs. fuel lines
New fuel filter
New fuel cap (needed that regardless)
New impulse line to cylinder
Removed cylinder... checked piston, rings, elbow for impulse line. It is clear. Piston has wear marks but doesn't seem excessive.
Checked fitting on top of tank. Both nipples on top of the fuel tank flow, and the one below does also. I sprayed carb cleaner through nipples using the spray tube.
Checked spark by grounding plug to spark plug hole and turning saw over. Sparks happen, but no idea if they are timed correctly.
Flywheel has cast-in-place tab on it matching crank. This is intact and not broken or damaged.
Another strange clue is that bubbles always flow in the purge system when I press the bulb. Bubbles come from the carb to the bulb, from the bulb to the tank.
Symptoms:
Pull Pull Pull, no start.
Pull Pull, run smooth for 3 seconds, then stop as if the run switch were turned off.
Compression:
I have not checked compression, but saw pull cord seems to have as much resistance as several of my other saws, especially for a 42 cc saw.
Compression seems good to me.
Saw falls very slowly when held by the handle, almost holds itself up.
I sealed off the exhaust and intake, without carb installed, and saw held 10 psi pressure and 10 in Hg vacuum for several minutes. I conducted test with a Mighty Vac through the spark plug hole.
What I have done to try to get her to run:
Vac Test
Pressure Test
Used coil from a 421 (maybe not right?)
Swapped plugs... resistor/non-resistor plugs
Carb Kit, and I checked and re-checked installation of parts
Sprayed carb inside and out, removed high/low jet screws and sprayed through all, did remove a bit of gunk from the high jet.
All new fuel lines
Checked and re-checked installation of purge bulb lines vs. fuel lines
New fuel filter
New fuel cap (needed that regardless)
New impulse line to cylinder
Removed cylinder... checked piston, rings, elbow for impulse line. It is clear. Piston has wear marks but doesn't seem excessive.
Checked fitting on top of tank. Both nipples on top of the fuel tank flow, and the one below does also. I sprayed carb cleaner through nipples using the spray tube.
Checked spark by grounding plug to spark plug hole and turning saw over. Sparks happen, but no idea if they are timed correctly.
Flywheel has cast-in-place tab on it matching crank. This is intact and not broken or damaged.
Another strange clue is that bubbles always flow in the purge system when I press the bulb. Bubbles come from the carb to the bulb, from the bulb to the tank.
