Well I was not going to come back, and I am really not trying to be abusive either.
However if that trimmer came into my workshop then the first thing I would do is get you to start it and verify what you are telling me actually happens.
Then I would toss the fuel in the tank, mix 1 litre of fresh 40:1, run your fuel out then replace it and try again.
This is because bad / stale fuel accounts for around 75% of all the jobs that come in the door.
Next I look up the Stihl book, check the factory settings and readjust your trimmer to how the factory says it should be.
From there is gets a fine tune using a tacho.
Next it is out in the yard to find somewhere that needs some trimming, usually I would run the entire tank through to be sure there was no other problems then call you back to come & pick it up, relieve you of $ 45 and get on with something else.
I would be fairly sure most on this list would do something similar.
OTOH if a customer came in and told me they were running 30:1 because they have decided the engine needs more oil than the factory engineers, then they had adjusted the carb by the amount the exhaust smoked rather than how well the engine burns the fuel . Followed by they only use it at 1/2 speed for whatever reason they think is justified (a position which by the way it could be running on either or both the low & high jets )
I would advise that it would be better set back to what the factory recommended.
The the custommer tells me his setting are fine because it has been working that way for a long time, my answer would be that the cummulative affect of the misuse and mal adjustments is what the trimmer is suffering from and if you want to continue doing the same you are wasting both of our times.
Now if you can fault this logic I will be amazed.
If I adjust the top speed to 13500rpm, the trimmer will not blow up today, or tomorrow but some time the rod will let go because I have the engine running 1500 rpm too fast. Now it might run for 20 years like this but eventually it will throw the rod.
If I run the trimmer too slow then the gas velocities are too low and because the timing is fixed the spark comes at the wrong time so the heat developement & dispersal is wrong and eventually this will cause grief.
Usually this will be excessive wear on the thrust faces of the piston &/or the bore and carbon build up around the exhaust port because the gas is going past too slow , the port is too hot and the exhaust contains too much oil.
If your wife put 1 grain of arsenic in your morning tea, it will not kill you today, or tomorrow ,or next week, or next month or next year but eventually it will kill you, saying she has been doing it for 20 years and you seemed to be working fine will not get her off the murder charge.
If you preffer an absurdly humourous simile .
I don't lie to my customers nor molly coddle or flatter them and they seem to appreciate strait talk as I have 3 week waiting time at the moment and this is the off season.
As before, good bye and good luck, I only haunt this forum for brief periods every few months.
