I have an old 25hp Tohatsu two stroke engine, think it is the M25C series - no serial number - from late 70's to early 80's I assume. It is a two cylinder single carb model with combined CDI/coil pack.
Problem is the top piston refuses to fire hence the engine not revving up as it should . Checked the reed valves and they are OK. Compression is good and same in both cylinders, new spark plugs fitted.
What happens is this: With the motor running and one pulls off the top plug wire, no difference. Pulls off the bottom plug wire and it dies immediately.
Swopping the plug wires around and starting the engine, it runs the same. Pulling off the wire on top cylinder, again no difference, pulls off the bottom one, the engine stops immediately again. This tell me the CDI is firing on both plug wires.
What mystifies me is the fact that it refuses to spark the top cylinder, even with plug leads changed around from CDI.
Strangely, although the top plug lead fires the bottom cylinder when swopped around it will not fires the top cylinder - even when I test the lead with loose sparkplug, it refuses to spark that, but will run the bottom cylinder on engine...
I checked the secondary windings resistance on the plug leads at spark plug ends and get same readings of 2782 ohms on each one. Checked all wiring from pickup coil to CDI and no bad places or joints.
Lastly, when I changed the plug leads back after I switched them around the motor fired on both cylinders for two seconds or so and went back in bottom cylinder firing alone.
What am I missing? Can anyone please point me towards a solution because Im desperate to get the problem solved
Problem is the top piston refuses to fire hence the engine not revving up as it should . Checked the reed valves and they are OK. Compression is good and same in both cylinders, new spark plugs fitted.
What happens is this: With the motor running and one pulls off the top plug wire, no difference. Pulls off the bottom plug wire and it dies immediately.
Swopping the plug wires around and starting the engine, it runs the same. Pulling off the wire on top cylinder, again no difference, pulls off the bottom one, the engine stops immediately again. This tell me the CDI is firing on both plug wires.
What mystifies me is the fact that it refuses to spark the top cylinder, even with plug leads changed around from CDI.
Strangely, although the top plug lead fires the bottom cylinder when swopped around it will not fires the top cylinder - even when I test the lead with loose sparkplug, it refuses to spark that, but will run the bottom cylinder on engine...I checked the secondary windings resistance on the plug leads at spark plug ends and get same readings of 2782 ohms on each one. Checked all wiring from pickup coil to CDI and no bad places or joints.
Lastly, when I changed the plug leads back after I switched them around the motor fired on both cylinders for two seconds or so and went back in bottom cylinder firing alone.
What am I missing? Can anyone please point me towards a solution because Im desperate to get the problem solved
