Spark Plug Gap: NGK vs. STIHL

[Merkava_4]

I bought an NGK CMR4H. NGK says they recommend the gap to be .028". STIHL says it should be .020".

The actual gap I measured with a feeler leaf is .025". Can I leave it at .025" or should I squeeze is down to .020" ?

This is for my STIHL FS 91 R string trimmer which I consider to be a hero machine.

 

[hacskaroly]

The actual gap I measured with a feeler leaf is .025". Can I leave it at .025" or should I squeeze is down to .020" ?

This is for my STIHL FS 91 R string trimmer which I consider to be a hero machine.

I typically gap all of my chainsaw spark plugs to .025. That is what I have my FS 91 R set at too.

 

[Merkava_4]

I typically gap all of my chainsaw spark plugs to .025. That is what I have my FS 91 R set at too.

Fantastic. Thank you sir for the quick answer.

 

[Coupe]

This is what stihl recommend so think I would stick to that.
AI Overview


Stihl's recommended spark plug gap is 0.020 inches (0.5 mm) for most of their trimmers, blowers, and chainsaws, including the FS 91. A proper gap is crucial for combustion and preventing misfires. While 0.020" is the standard, larger engines may require a slightly larger gap, such as 0.025" (0.635 mm).
k to that.

 

[Merkava_4]

The trimmer has never ran better since I installed that NGK with the .025" gap.

I used to have kind of an uneven idle speed. Now it's rock steady. Very pleased.

 

[lehman live edge slab]

Cmr 4h? Thought all the stihls with small plug called for cmr6h which is cooler than the 4 you used. But maybe some do call out for the 4 instead.