FS-90R trimmer troubles

[NuclearNick]

Hello, new member here so be kind...

I have two FS-90R trimmers, both about 5 years old. Have had pretty good luck with them over the years, but in the last year they have been getting harder to start and keep running. Just dusted them both off for the spring, put in new fuel (with 2 cycle oil), checked spark plugs (new last year), reset governor to factory settings (both H & L: to 3/4 turn open), cleaned air filter). For clarity, I'll call them trimmer A and trimmer B:

Trimmer A: Starts easily in full choke, continues to run when choke put in run, but dies in about 5 seconds regardless of throttle position.

Trimmer B: Starts easily in full choke, runs great under load in run at full throttle. But after about a minute of run time, slows down and dies.

Recommendations? I'm handy and can repair, but I am admittedly not a small engine mechanic so could use any pointers from the crowd. Trying to avoid several hundred dollars of labor at the local Stihl dealer...

Thanks!

 

[Bedford T]

Do you use corn gas?
Was there gas in tank?
Are air filters clean?
Was the rubber replaces like fuel lines impulse line replaced within 2 years using corn ?

If you answer yes once excluding the filter, I would do a pressure vac test, if you say you can't I would say replace the rubber and then replace the carbs if you still have issues. And enjoy your trimmers.

 

[NuclearNick]

Thanks Bedford T:

- never buy ethanol, just using regular unleaded + stihl 2 cycle (orange bottle)
- good question about gas in the tank, but yes
- yes, air filters clean, I actually removed them entirely and got the same engine response (then put them back on)
- I haven't replaced any fuel lines. I'm assuming I can buy the line at the dealer by the foot or something. Any particular lines suspect?

Regarding carb replacement - is the carb a plug & play install (just bolt it on)? Or will some setup / tuning be required? Wondering if this is a job for the pros or if a hack like me can do this reliably.

Cheers,

 

[Bedford T]

You need it tested but based on your statements all rubber should be replaced as well. Your carb should be tuned. You might want someone with the tools to do it. Nice trimmers.

 

[DND 9000]

Also check and adjust the valve clearance of the inlet and outlet valve. Might be out of specification. (Valve clearance is 0.004 inch (0,1mm) on both valves) It`s also possible that the valves have carbon built up, because you write that you use the orange bottle 2 cycle Stihl oil. (As I know, this is the mineral HP oil). Stihl says that all 4 Mix engines should be run with the fully synthetic HP Ultra, because of carbon build up on the valves and valve seats. I would also replace the fuel filter in the tank and carburetor and give the carb a ultrasonic clean and install new diaphragms and gaskets.

 

[NuclearNick]

Good news & not so good news...

Picked up new carburetors from the local dealer (about $40 apiece but saves me a lengthy rebuild). First trimmer runs like a champ.

Second trimmer threw me a new curve ball. Apparently during all my bumping around, the fuel line fell off inside the fuel tank (it's laying in the bottom). Tried to pry off the little plug the fuel lines go through, and the dumb little plastic tab snapped off (see picture attached). Anyone have tricks for reattaching the fuel line without pulling the plug? Any tips on removing the fuel tank? Looks like it is formed in 2 pieces and could be removed and split, but not sure if that's a bad idea or not.

Also couldn't find this little plug on amazon or ebay anywhere, wondering if it is even sold separate from the tank?

Would appreciate any tips from the crowd...

Thanks, Nick

 

[Bedford T]

Yes you empty the tank and pull straight up on plug. The dealer will have a replacement. I think it comes with an O-Ring if it does not get one. Put a little mix oil on it so you can push it back in and the fuel will dilute it. Replace the part in the tank too

 

[DND 9000]

The connector that you need is part no. 4180 350 1402 and comes with the o ring. Use Press fluid OH 723 part no. 0781 957 9000 to install the new connector. As I see from your picture, you have the old style position 90° angle of the connector element on your fuel tank. That means you need 2 fuel lines that have to be cut to lenght. I don`t know which carburetor you got from your dealer, but I think you got the new version with barbed connector. Because of the fuel line lenght see file attached what you need. I would also replace the pickup body in the tank part no. 0000 350 3502 and put in a new hose in the tank from the pickup body to the connector. This tank inside hose is sold seperatly and has no part number.