I have a Stihl MS291 that will not start. It has a weak spark; certainly weak compared to my MS461. Tested the wiring and kill switch, no problem. New spark plug, and I replaced the ignition module, gapped to .010, no change. Now I suspect an issue with the flywheel magnets. There are four magnets; two on each side of the flywheel. On one side the magnets are marked N/S and appear to be ok. I tested them with another small magnet and they seem strong with the proper polarity. On the other side of the flywheel, there are no polarity marks (at least on the side facing out). These magnets have little or no magnet pull and I can't tell any difference in polarity. Question: should I expect the magnets on both sides of the flywheel to test the same?
No start -- Flywheel magnets?
- Thread starter scottz
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- stihl ms291
No, you should not.
The second pair of unmarked "magnets" are counterweights- they mimic the weight of the actual magnets that cause the coil to fire to keep the flywheel balanced as it rotates at huge speeds.
They act a little like the lead balancing weights added to your vehicle wheel rims to balance the rotation of the tyre. If they were not there, the unbalanced flywheel would cause fast bearing and oil seal failure on that side of the crank.
The second pair of unmarked "magnets" are counterweights- they mimic the weight of the actual magnets that cause the coil to fire to keep the flywheel balanced as it rotates at huge speeds.
They act a little like the lead balancing weights added to your vehicle wheel rims to balance the rotation of the tyre. If they were not there, the unbalanced flywheel would cause fast bearing and oil seal failure on that side of the crank.
291's are a temperamental kind of saw- I would be pressure and vacuum testing as a matter of course if it is hard to start/wont start.