Ht 131 Back fire broblem?


New Member
I have an Ht 131 that misfires under load (Nasty popping noise). Tried everything cant seem to fix it. Will only do it under load.

Machine is 3 years old. Not used that much just changed sprocket for first time. Replaced Carb(had a small gasket leak), Removed muffler screen (No carbon build up found), replaced ignition module, checked flywheel gap, new spark plug, inspected wires from trigger for grounding short, vacuum test good, compression test good, and rebuilt clutch, tried adjusting carb. No luck so far

Took machine to local dealer no luck there on a fix so far. Dealer will be contacting Stihl for assistance but no luck so far.

Any Ideas? I am at a loss.


Active Member
Might want to check that the flywheel is still in the correct spot. Timing reduction would cause early detonation. Low octane fuel could be an issue as well?

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New Member
Will check put problem started before saw was ever disassembled since new. The fuel is a good point but both by Fs 550 and 555fx have been using from the same tank with no issue.


Well-Known Member
Its harder to fire a plug gap under load than free revving.

Take out the plug and close the gap by about 10 thousandths and see if this clears it up. If it does then its showing that something in the ignition system is weak...often a coil assembly is the culprit.

PS not a saw mechanic, so I have no ohm specs on coils for saws, but I can not tell you the number of guys who have I have helped identify a weak component on a race car this way.

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