Stihl Trimmer Issues

[TWG1572]

So, I have a "new to me" FS 55 RC trimmer. Had it about 2 years. Been feeding it 91 ethanol free and stihl synthetic oil. It's always been a bit balky to start and needed to run with the choke on slightly to avoid stalling... I figured possible carb issues, but it never was a big enough issue to monkey with.

Two weeks ago, it wouldn't start. I took the carb screws back to their recommended starting position, did a lot of pulling and got it going again. somewhat. It's got the 3 screw adjustable carb. walbro (sp) maybe?

Now, it will run at idle but it starts stumbling when I hit the gas. I have to "work it" to high throttle by slowly pulsing the trigger back and fourth. Slowly, I can go a little faster with each pulse. I can finally ease it to high throttle, but it bucks and misses initially. It will miss for 5-10 seconds, then catch and take off.

Yesterday, it started something new. Once it was running at high throttle, every time I let off it just died. Flat out. No coughing, it just stopped like I hit the on/off switch. It does this every time. I unscrewed the gas cap in case there was a vent issue. No change. It seems to be happy when locked on full throttle, and ran as long as I wanted it to.

My assumption is that I've got carb issues and need to rebuild or just replace. But with all the new issues, I wanted to get opinions. I'm by no means a 2 cycle expert.

Thanks in advance!

 

[punisher]

You nailed the diag, it seems a carb problem, running lean/fuel delivery problems.

My first step on those is to get the number off the carb and google it, check E-bay as well. I have bought 2 Walbros for trimmers ($18-21 each) vs $12+ shipping for an overhaul set. I am naturally lazy, so $8 extra for a complete carb is a simple choice. I did eventually get carb kits for both those carbs and rebuilt them (it gave me a chance to use my new ultrasonic cleaner), so I have 2 carbs ready to go whenever a problem arises.

 

[flanso]

I recently experienced the same symptoms with my 9 year old FS 85. I rebuilt the Zama carb which yielded little improvement. I was pleasantly surprised to find that the dealer price for a new carb was only 37 bucks. I bought a new one on eBay for even less and now my trimmer runs like new.

 

[99dej]

I've got a Deere trimmer, would be hard to start, and then run on a fast idle. All the time.

I was recommended Polaris Carbon Clean fuel additive, used it according to the bottle, and switched to a premium fuel. Fixed. Idle is back to normal, and its running great.

Don't know if it would work with yours, but for $8 I was willing to give it a try.

 

[Silk]

Check the exhaust before you get too involved - most Stihls should have a removable spark arrestor,remove it and clean the gauze.

 

[shooter250]

I have a FS 85, and I was recently having problems with it dying when I gave it a lot of gas. It ended up needing a new fuel filter. The fuel filter is inside the tank at the end of the pick up hose.

Just another thought to check. Good Luck.

 

[TWG1572]

thanks for all the suggestions guys! ended up being the carb. I decided to just replace it, and it runs like new. I could have rebuilt it, but the price difference wasn't enough to make it worth the time.