# Sthil trimmer probs , won't rev up



## manalone44

Hello all

New here today. I'm 44, I had a lawn care biz for 8 years, am a automotive tech, and have for the most part fixed all of my stuff myself , but I need some help with this one.

Model FS 85, it was running fine then got rained on some and now it won't rev up , it will idle all day. I have checked : fuel filter and lines , muffler and port clean , carb removed and cleaned , fuel bulb is holding fuel , adjusting the high makes no difference , plug is clean and tan in color , I haven't put in a gasket set yet ...... any thoughts?

Thanks


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## Deathrite

i think i am safe in saying you changed the fuel out for new.

how about the "wheel" above the needle? does it turn? if so thats the issue. replace gaskets. 
basicly you seem to have done all else i can think of right now.


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## manalone44

not sure what u mean by a wheel above the needle , but i'll look , i'm going to go further and pull the intake and see if the pump port is blocked some how , guess i just don't understand how it could run fine and then not run on high , it has always been hard to start , and my 29 farm boss has been junk since i bought it , with constant carb cleaning , it runs best at WOT , mid range is nothing but sputtering .....


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## Deathrite

the metal wheel looking thing above the lever that moves the needle. the tech name has excaped my mind so i apologize for that. i have seen that break seal with the gasket and cause problems. 
if you do take the lever off (and you might know this already) be careful of the little spring under the lever. it will fly to Oz if you let it. 
if you do happen to lose it i do have a part number for a spring that works.


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## manalone44

the fuel pump gasket ? now there was a small oval clear gasket that looked like a seal for a oval bung plug in the needle side that came out while i was cleaning it but the bung plug is still there and looks sealed ....


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## rotti1968

I would go back to the carburetor, this is a regular issue I have been seeing . for what ever the reason customers are using there trimmers without issue, it runs out of gas or they put it away and go to use it the next weekend and it will not come up to speed. I just did an fs 80 yesterday with the same problem you have. I removed the carburetor and cooked it in our sonic cleaner for about an hour . removed it blew it out with air and reinstalled it and it worked like new. There was something restricting the high speed side of the carburetor and the sonic cleaner took care of it .


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## manalone44

that sounds about right , but i have no sonic cleaner , bout the best i can do is a pan duct taped to a orbital sander , do you know where that high speed hole is , it is a zama c1q-s45 and or rb66 ???


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## Deathrite

while the orital sander and duc-taped pan sound interesting i dont really think that will do the required cleaning. 
the gasket i was meaning is the metering diaphragm. if the metal ring breaks loose from the gasket material it allows air in. this might not be the issue here but it is simple to check. if the ring turns when putting minor turning force on it then it is in need of replacement. 
i agree that the high speed jet is the more likely problem. it SHOULD be under the metering lever. but if there is no high speed mixture screw i am not sure if that will be in that place. 
have seen small sonic cleaners for about $30. but they are SMALL. a disasimbled 2-cycle carb might fit but thats about it. http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=3305


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## rotti1968

http://www.zamacarb.com/pdfs/TechGuide_2007.pdf

There may be info in here to help you out.


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## geogrubb

Before you start tearing things apart, if it will idle, dump out the fuel thats in it and create a mixture of 1/2 Chevron Techron, (available at all autoparts stores and wally, it's in the black container) and 1/2 fuel mix enough for the engine to idle for 20-30 minutes, DO NOT REV THE ENGINE or bad stuff can happen, when it is finished replace with regular fuel and idle for a few minutes before you go to WOT and it should be ok. Post back if it makes a difference. Have a good one. Geo


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## Twmaster

Deathrite said:


> while the orital sander and duc-taped pan sound interesting i dont really think that will do the required cleaning.
> the gasket i was meaning is the metering diaphragm. if the metal ring breaks loose from the gasket material it allows air in. this might not be the issue here but it is simple to check. if the ring turns when putting minor turning force on it then it is in need of replacement.
> i agree that the high speed jet is the more likely problem. it SHOULD be under the metering lever. but if there is no high speed mixture screw i am not sure if that will be in that place.
> have seen small sonic cleaners for about $30. but they are SMALL. a disasimbled 2-cycle carb might fit but thats about it. http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=3305


So what do you use as a cleaning agent? The stuff H-F recommends for use in that little cleaner says not to use on aluminum or magnesium?


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## geogrubb

After doing a little checking it seems some FS-85 have a speed limiter built into the ignition module, maybe it got messed up when the unit got wet. Check the TI below. Have a good one. Geo

TI 41.97
A new version carburetor without speed control valve will
be installed instead of the carburetor with speed
control valve on the machine numbers listed
below.

Model Machine no. /
Introduction of modification
FC 75 X 37 801 959
FS 75 X 37 878 261
FS 80 X 37 759 999
FS 85 X 37 838 653
HL 75 X 37 761 799
HS 75 X 37 810 310
HS 80 X 37 810 310
HS 85 X 37 810 310
HT 75 X 37 772 428

At the same time, the former ignition module
will be replaced by a new version with
integrated electronic limitation of the
maximum speed (referred to below as
(Electronic speed /Limitation).

The ignition module with ESL can be identified by
the marking [[[[ = 1306 or 1307 
Ignition module "1307" only differs from version
"1306" through the additional insulating hose ()
for the ignition cable and is generally supplied as a
replacement part.
The insulating hose () is not required for the
BG and HS machines. However, the new
replacement ignition module can be installed
with insulating hose.


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## rotti1968

Most of stihl coils have a speed limiter built into them. When one of those goes it normal goes to a no start condition.


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## rotti1968

Twmaster said:


> So what do you use as a cleaning agent? The stuff H-F recommends for use in that little cleaner says not to use on aluminum or magnesium?


This is the product we use in ours it works great....
http://www.omegasonics.com/industrial/chemistry.shtml


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## geogrubb

I cleaned the carb from an old Weedeater trimmer using the HF powder and a solution of ZEP Purple in the bigger cleaner ($79 one). I thought since everyting about the trimmer smelled like varnish it would need a good cleaning so I ran it for three 8 minute cycles with heat, I didn't bother to look between cycles(not a good idea), it came out almost totally black, however, it was clean and works, just can't touch it without getting black residue. Somewhere I missed the part about "Read and Follow Instructions". Have a good one. Geo


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