Help with Stihl FS85 Trimmer

[tillboy2001]

I've got a FS85 trimmer from Stihl. It will run just above idle but dies if you try to give it more throttle. I've taken the carb off and taken it apart to blow it out. Also replaced the coil/spark plug wire since the plug wire was coming loose on the end that connects to the plug. I can't figure out why it won't run right, as in fast. Like I said, it'll only run just above idle. It sounds as if it's starving for fuel. I checked the fuel filter and it looks ok.

I noticed on the new coil, there is some adjustment there. Meaning it can be very close of farther away from the flywheel. I didn't see any specs in the book on what distance to place the coil from the flywheel....but I don't know if that has anything to do with my problem or not. It ran this way before I replaced the coil. This trimmer actually belongs to an in-law - I'm trying to fix it for him. In the past I've been able to blow out the carb to fix something like this. I can't imagine it being anything other than the carb or coil...there's not much else to this simple machine. I'm still leaning towards the carb. Maybe I didn't get it cleaned out well enough? Who knows.

Any ideas?

 

[westbrooklawn]

Sounds like a fuel problem to me. Could be that carb is still dirty, filter on intake line plugged, or deteriorated fuel lines (a very common problem which is sometimes hard to see). Sometimes when my 2 cycle equipment starts to act up I run a little Sea Foam in with the gas.... it is amazing what this stuff will do. I'd try that first, and also replace the fuel and vent lines if they are more than a couple years old. Oh... also make sure your air filter is not plugged.

 

[tillboy2001]

Thanks. I guess I'll give the carb another cleaning and verify the fuel line/filter.

 

[Flatheadyoungin]

does your's have the littls plastic stops on the H and L speed adjustments? if so, take them off and you can adjust it as needed....

it's the little black plastic caps on the H and L adjustments, and they will only allow you to turn the screws so far......very limiting

 

[tillboy2001]

Yes it has those. I tweaked those but it made no difference. I suspect something is still clogged in the fuel system somewhere...I'll keep working on it.

 

[Flatheadyoungin]

i'll put my money on the collapsed fuel line or clogged filter.


i know you said you cleaned it but there ususally is a small filter screen in the carb too......sometimes, i just remove it with a pocket knife.....

Yes it has those. I tweaked those but it made no difference. I suspect something is still clogged in the fuel system somewhere...I'll keep working on it.

 

[afternoonhandyman]

I'm having the same problem with my Dad's FS-85. It has the Zama carb with 1 (one) adjusting screw on the carb, which is not a needle, just flat-ended with smooth shaft for about 1/4" before the threads. There is a 2nd on the throttle cable cam. Can someone provide me with adjustment procedure on these? I've spent 6 hours Googleing and ASKing and can only find info on the 2-screw carbs. The manual thaqt came with the '85 shows the 2-screw carb. No hidden or covered screws either.

Thanks in advance

 

[PILOON]

Most of these small 2 strokes (saws trimmers etc) have a flopping gas pickup in the tank.
Generally a soft rubber line with weighted end that contains a felt filter.
If the filter gets clogged that will limit the fuel flow and even water can clog it.

Just a thought that might help. Good luck.

 

[Bird]

Most of these small 2 strokes (saws trimmers etc) have a flopping gas pickup in the tank.
Generally a soft rubber line with weighted end that contains a felt filter.
If the filter gets clogged that will limit the fuel flow and even water can clog it.

Just a thought that might help. Good luck.

I ran into that little problem with my Mantis tiller; easily corrected after I learned what the problem was. And also with the Mantis, I had a similar problem as originally reported in this thread. It would start and idle just fine and the instant I tried to give it gas, it would die. That one took me awhile to find and correct, but it was actually nothing more than a simple carburetor adjustment.

But I also learned with the Mantis that you must allow it to idle and warm up two to three minutes before using the throttle or it'll die. My Stihl string trimmer has never had that problem.

 

[dennis1960]

Stumbled on this site while searching for parts. I just had the same issue with a Stihl FS80. Pull the muffler off and you will probably find the exhaust port is plugged.