Two stroke string trimmer, maybe six years old. New plug, and I have confirmed a fat blue spark against the head. Fuel is fresh 50:1 and I can see it moving in the primer bulb. It will not fire even once, not even a cough on starter fluid. Compression feels okay pulling it over but I have not measured it. Where do I go next?
Make sure the plug is the right heat range and reach. A slightly long plug can contact the piston and a short one puts the spark in the wrong place.
Check the exhaust port and the spark arrestor screen too. A carbon blocked muffler will stop a two stroke firing, and on a six year old trimmer that has run rich it is common.
The arrestor screen was half blocked, though it still would not fire with the muffler off entirely.
Then it is not the exhaust. Clean the screen anyway while it is apart and go and look at that flywheel key.
Pull the muffler and look at the piston through the exhaust port while you are there. Free look at the thing you would otherwise be guessing about.
@probe_to_ground · 9mo ago · 4 replies
If it will not even cough on starter fluid with confirmed spark, stop looking at fuel delivery. That is the split point in the diagnosis.
A two stroke with good spark and fuel put directly into the cylinder that still does nothing is usually one of:
The sheared key is my first guess on a six year old machine, especially if it has ever hit something solid.
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@probe_to_ground · 9mo ago
There is your answer, probably. That impact is exactly what shears a flywheel key.
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@cast_iron_carl · 9mo ago
It hit a fence post last summer, which I had entirely forgotten about.
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@weekend_margin · 9mo ago
Half the diagnosis on these is remembering what you did to it last year.
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