OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Chainsaws and Concrete Cutters Petrol Chainsaws and Concrete Cutters Coil test

Can you test a coil out of a chainsaw???

Mower repairers sometimes have a test-board for checking ignition units and coils. This can be done in various ways, most of them electronic. If you wanted to test it yourself you'd probably need to set up a flywheel the same diameter as your chainsaw's flywheel, on the shaft of an electric motor, and mount the coil close to the flywheel. If you decide to try that, make a proper, strong rig with a guard around it: you don't want bits to come loose or fly off. Remember, you need to use a flywheel with a magnet embedded in it, or there won't be any spark regardless of how good your test rig is. A single phase induction motor from a smallish electric fan would probably have a maximum speed of 3,000 rpm. I know your chainsaw probably reaches about 14,000 rpm, but it just isn't safe to run a test at that speed on a home-made rig, in my opinion.

Yeh thanks Grumpy. I'll get Stihl in Bundy to look at it tomorrow. Tryed drying it with a hair dryer for 3 hrs and still no spark. Also working on a Air Compressor with a GX 160 Honda that got flooded as well. Its up and running fine after a good clean out.

Dave, except when you are looking for something unusual like intermittent breakdown at high speed, the standard spark test using a spark plug with an increased gap, will give you the answer. Just remove the spark plug from the mower, connect the mower's plug lead to a known good spark plug, ground the metal body of the plug, and pull the starter. If you get no spark across the good spark plug, check the gap between the flywheel magnet and the module. If that gap is correct (nearly always, the thickness of an ordinary visiting card), step two is to disconnect the kill wire at the ignition module, and repeat the test. If it still does not spark, you need to check the grounding of the ignition module (it sometimes gets rusty, or has not been properly attached). If there is no spark when you know all these things are correct, it is time to check the resistance from the kill wire terminal to ground, and from the high tension (plug wire) to ground. The kill wire terminal to ground should be about 1 to 3 Ohms, and the HT wire to ground should typically be about 12,000 to 20,000 Ohms.

If it passes those tests but doesn't spark at all, you've messed up the tests. If it passes those tests, and sparks at cranking speed, but you suspect it is erratic at high speed, you need a test under load on a special tester (whether home-made or the one the repair shop may have).