Husqvarna 455 cutting out under load

4CornersPuddle

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I traded for a Husqy 455 recently. It's a low hours saw, well maintained, treated well.
After I reset the carb adjustment limiters and opened the muffler to the 85% outlet to inlet ratio, the saw really picked up performance, running smoothly, starting easily. It was quite dependable and impressive for what it is (a 455).

However, it has developed what sounds to me to be an erratic miss under load. It 4 strokes appropriately out of the cut and clears up to 2 stroke if I hold it up so it cuts "lightly". In other words, I'm not letting the weight of the saw influence the cut.

But if the rpms drop a bit, but not nearly to the "lugging" stage, it will begin to miss off and on, obviously losing power. I've changed spark plugs twice and looked for a loose wire intermittently grounding out. There does appear to be a very small gap between the kill switch wire electrode and its ground position when the switch is in the run position. My thought was a spark may have been jumping this gap at times. I pulled the wire from the kill switch and insulated it with tape with no change in the cutting out behavior.

Any ideas what could be causing this stutter?
 

3000 FPS

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That is hard to say. I would have guessed the kill switch wire also.
But I would pull the coil and make sure everything is clean before putting it back on.
I do not remember how the spark from the plug travels back to the cylinder and then to the coil because we are talking a plastic saw here so it could be using a wire.
Then of course there is the coil itself or the plug wire could be going bad.
I would not suspect the carburetor since you have it tuned correctly, and I would not suspect the crank seals since it did tune correctly. It sounds like spark to me. What gap do you use for the spark plug. I always use .025".
Keep checking everything with the spark.
One last thing pull the kill switch wire from the coil not from the switch. The wire could be shorting out somewhere before it gets to the switch.
 

4CornersPuddle

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3000 FPS Thanks for your comments. I will do those ignition checks you suggest.
Spark plug gap was .040" when I got the saw. I reset gap to .020" on that plug well before the problem started.
Since then I've tried 2 other plugs.
It may be a bit of time before I get back into this saw. I'm running saws 7 days a week for two different arborist companies and have 3 other 60cc class saws that I'm using daily.
 
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