Stihl trimmer will not run wright

[TheHammer]

Hi I have 4 year old Stihl fs85r trimmer that will not rev up after warming up, which took 5 minutes, it would bog down and shut off.

[genesis215]

I'm not an expert in these things, but I would suggest removing the spark arrester that is in the muffler. It should be right at the entrance of the exhaust pipe. If you have already removed it and it doesn't run any better, then I would replace the fuel filter and spark plug. If this fails too, then remove the muffler and clean out the exhaust port as it may be clogged with carbon.

One last thing that I would definitely do no matter what would be to pour a little bit of "Seafoam" straight into the carburetor, let it sit for 10 minutes, and then restart it to clear the carburetor (and burn out the carbon). It will smoke like crazy for a bit, but once it passes it should run better. My 2-cycle stuff runs much better now that I have run "Seafoam" through. Hope this helps.

[TheHammer]

I had put a new carburetor last December, and it work fine but when I put 2-cycle fuel
in it this past Thursday it bodged down then it smoke like crazy then rev up for 10 minutes then bog down.

[kogafortwo]

Try new fuel lines - make sure to use the black Stihl fuel line from your dealer. You need about 1 foot of it cut into two lengths to match the vent line and the pickup line. Put a new fuel pick up on the new fuel line.

This is about $4 worth of parts and 20 minutes of work. It is hard to get the new lines through the grommets in the tank. A little silicone spray helps.

Also check that your carb mounting screws are tight. Also take the carb off, take off its mounting gasket, and tighten the two torx head screws by hand that hold the carb mounting plate to the cylinder.

This is the easy stuff. If it doesn't work, you have an air leak somewhere that you will have to track down or have an experienced mechanic look for. The labor charges are what will kill you, that's why I do my own work, but air leaks are a pain and I don't have much luck with them.

[TheHammer]

I found out it was old gas, so I made a new bach 2cycle , it ran awsome.

[kogafortwo]

Cool, I'm glad it was something easy. I am a stickler about my fuel for exactly the reason you just described.