2-stroke question, not a motorcycle.

Lemonhead

Member
Jan 31, 2002
16
0
I have a Stihl FS-85 weed trimmer. It stalls out on full throttle. Runs great with the choke a little open, stalls when I open the choke all the way and squeeze the trigger, even with the air filter off, the spark arrestor is clean, the fuel filter is clean, spark plug is good. Gas mix is fresh. It's a 1999 and has been runnig great all these years. You could clear cut forest with the damn thing when it's on the pipe. I've been running the same pre-mix in it as I have my KX500. Phillips race 100 octane unleaded with castor oil. I'm thinking it's not getting enough fuel with the choke full open at full throttle. I blew the fuel lines out. Only likes to run and idle with the choke cracked a little. I think it's starving for fuel at WFO. What do you think??? Thank you for your thoughts.
 

2-Strokes 4-ever

~SPONSOR~
Feb 9, 2005
1,842
4
Missouri
Yup, clogged jet. Fuel doesn't last anymore... more than a couple months old, pitch it.
 

mideastrider

~SPONSOR~
Jul 8, 2006
827
1
Most likely needs good cleaning. May want to go ahead and get a carb kit before you start. 13 years old a new diaphragm couldn't hurt. Plus you will have any gaskets and parts that may need.
 

RM_guy

Moderator
Damn Yankees
LIFETIME SPONSOR
Nov 21, 2000
7,045
208
North East USA
Check the fuel filter in the tank too...if it has one. Most weedwackers I have had have 'em and they get plugged form time to time.
 

pesky nz

Member
Sep 13, 2010
296
0
I would fit a Genuine carb kit, most of those type carbs have 2 small press in round filters and they clog and can not be blown out without removing them and that usually wrecks them so your carb kit should include metal screen filers (about the size of theend of a pencil and rubber diaphrams. the filter in the fuel tank is more a throw away than a clean and re-use and all fuel hoses must be tested for small leeks or cracks ( I always find saws and similar power products more frustrating than any bikes) lots of these things have high and low fuel mixture screws, in for lean and out for rich and set high speed midway between screaming and burbbling at full thottle and low speed for best pick up from idle all done with a clean air filter in place.
 

jason33

Member
Oct 21, 2006
655
0
first off check the butterfly! some open to far,and actually close the air off (just like letting off the trigger), i have dealt with this problem on lawn mowers, boats, tillers ect...
also there prone to air leaks, from the carb screws loosening up good luck
 

BSWIFT

Sponsoring Member
N. Texas SP
LIFETIME SPONSOR
Nov 25, 1999
7,926
43
I'm with RMguy, filter in the tank is starving the carb. Simple and cheap fix.
 

FNG

Member
May 2, 2008
97
0
I am fighting this same battle with my 10 year old Echo weed trimmer.

I bought the factory rebuild kit and installed it: no change

Blew out all of the orifices and cleaned the carb: no change

I bought the hose kit with new filter and such: no change

Tried new fuel with different mix ratios: no change

I even ran some 50/50 110 with premium: no change

I don't know which way to go now. I could replace the carb for 55$. Maybe time for a top end? Not worth the $$

I suppose after 10 years it is time to buy new. Maybe 4 stroke now?

The worst part is I need a heavier rear spring for my dirtbike!

Weed whippey or spring? HMMMM
 

mideastrider

~SPONSOR~
Jul 8, 2006
827
1
FNG, all that and no change. Maybe time for a topend or it may have an air leak somewhere crank seals or the case maybe leaking.
Don't worry about it. Chunk it in the corner go get the rear spring and ride.
 

sharky243

Member
Dec 14, 2008
246
0
Check the fuel lines and filter. The lines split after awhile. Make sure the fuel is fresh and of good quality. We tell all our customers at the shop to use 89 octane or higher. Don't use that E-85 crap !! If everything else is ok ie; spark arrestor screen, exhaust port, compression, ignition etc, then you most likely will need to thoroughly clean the carb and install a kit. I've had some carbs so bad that they had to be replaced completely. One other thing that can cause your problem but is rare, is a crankcase air leak. This can be a worn seal, loose cylinder, leaking gaskets, etc. It will cause the air/fuel mix to lean out and cause the symptoms you are describing.
 

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