Stihl fs90r,strimmer

[Ricky.]

Hi,sthil fs90r I've been working on 4 mix with valves,new non genuine carb,customers choice, had it running fine leave it 20 minutes back to tuning it again 

Erratic revving ,have done h. L. And cable tension screw,just want to check if carburetor is a lemon or I'm missing something thanks. 

[TurtleWoods72]

I have the same machine. Ran like a champ season after season. Then I bought some other machines and due to one being bigger and more powerful (Kawasaki 45cc) and another being smaller and more manageable (Kawasaki 23cc) the Stihl got sidelined.

 

Came to use it again and the clutch shat itself, so I replaced that with OEM clutch and ran it a few times. Then I left it with fuel in for a long time and the carb got gummed up.

 

Opted for Chinese copy carb off amazon and fitted easily enough. Ran like a champ from the off. 
 

Used it a few times and noticed it was going out of tune quickly and now cuts out completely after a very short time of use (10-20 mins).

 

I’ve got a few spare cheapo carbs to throw on it, but frankly if they’re all as bad it’s a waste of time swapping them. I’d either buy a genuine carb or get access to an ultrasonic cleaner and maybe a rebuild kit for the standard carb.

 

i only own two pieces of Stihl equipment, and was a massive fanboy 15 years ago. I’ve had problems with BOTH Stihl machines since and none with my other kit. Doubt I’ll ever buy a Stihl machine ever again unless it was cheap beyond belief.

[Muddy42]

On 12/09/2025 at 15:51, Ricky. said:

Hi,sthil fs90r I've been working on 4 mix with valves,new non genuine carb,customers choice, had it running fine leave it 20 minutes back to tuning it again 

Erratic revving ,have done h. L. And cable tension screw,just want to check if carburetor is a lemon or I'm missing something thanks. 

 

I prefer putting a carb kit in a genuine carbs to non-genuine replacement.  You could try that.  Does the tunning change when you tilt the machine in different positions?  That and erratic revving could be an air leak.  I'd P&V test.

 

[pleasant]

Have you checked and set the valve clearances, and if so, did you do it on the correct stroke?