Husqvarna 346 XP backfires,

[1974mj]

Bit of advice please people, I have a 2009 346xp, never had any issues, regular serviced, always use XP 2 stoke oil (opinions on that!?) today after approx 3 hours work it stopped and now backfires on starting, can't see any obvious faults. Any suggestions? Ta.

 

 

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[H-A]

Could be sheared woodruff key locating flywheel.

 

So timing out.

 

H-A

[GardenKit]

It does sound like a timing issue, so it could be the flywheel sa H-A says, so worth a check.

But before getting too involved, change the spark plug, it could be that simple.

 

I had one like this a few years ago and it turned out to be the ignition module (coil). The internal timing control had failed.

[spudulike]

The only saw I have known backfire like this was a Stihl 028 and it scared the bejusus out of me - just wasn't expecting it!

 

It sounds like the flywheel key has failed and the ignition is well in retardation.

 

Barrie has listed the other possibilities, the ignition coil modules have some trick advance retard circuitry in them and it could have gone tits up.

 

A good way to see if the flywheel has slipped is to pull out the sparkplug, allign the coil with the flywheel magnets (it will pull it in to position) and then place a screwdriver end on the top of the piston and turn the flywheel anti clockwise and see if the screwdriver rises a little before falling.

 

There should be circa 27 - 32 degrees of advance on the flywheel position when gripped by the magnets to coil before TDC.

 

Sorting out the flywheel key, if it is that, will be a PITA - I am doing this in a big way on an old 066 at the moment - it may be possible to re key it if you are inventive or just get a new/secondhand one.