Stihl 4-Mix FS 91 R surging at full throttle

[Merkava_4]

It runs fine at all other engine speeds, just surges at full throttle. Usually in a situation like that I can adjust the high speed mixture needle and the issue will go away, but not this time. The engine has low hours and has not had its valves adjusted yet; do you think that could cause a surging issue?

 

[Merkava_4]

The more I mess with it the more it seems like it's starving for fuel at the higher RPMs. I might try retrieving the fuel filter out of the fuel tank and have a look at it.

 

[Gaston]

In my experience it’s quite easy to hit the rev limiter on the coil on these and their brothers. Are you sure your not bouncing off the limiter?

 

[Merkava_4]

The fix was a new tank vent; now it runs fine.