Stihl FS45 weed wacker won't start

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xman23

xman23

Minister of Fire
Oct 7, 2008
2,638
Lackawaxen PA
Anyone know what's going on with this thing?
It was running fine, but the cap that holds the weed wacker spool broke. I got a new one, clamped the machine in the vise upside down to put it on. Now I can't get it started. Surely I've pumped the primer to much, gas coming out everwhere. Pulled the plug and as I turn it over it spits out fuel out of the plug hole and the carb. A lot of gas everwhare. It does have spark a a new plug.

Is it just flooded and needs to dry? Or did some thing hung up in the carb? The carb looks simple and doesn't look like there is a bowl and a needle valve, but is three one in there that may be hung up?

Thanks guys for any help here.
 
most likely flooded so pull the spark plug, give it few pulls to help clear any fuel from the bottom end and walk away for an hour or so. Put the plug back in and try starting.
 
rkshed said:
most likely flooded so pull the spark plug, give it few pulls to help clear any fuel from the bottom end and walk away for an hour or so. Put the plug back in and try starting.
Click to expand...

No good. With the plug out, it's spitting raw gas out the exhaust. Put the plug in and it hydro locked

Anyone know where I can find a explored view of the carb. I'll do a Google search.
 
Is it a Zama C1Q-S66? Here is a general schematic: http://www.zamacarb.com/carburetors/431

Sounds like the needle is stuck open. Could be the spring under the needle lever has failed and needle doesn't stay seated until pressure is applied to lever by the metering diaphragm.

These carbs are available as AM on fleabay for $15. When they are that cheap, I don't bother with a $10 rebuild kit.
 
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dougand3 said:
Is it a Zama C1Q-S66? Here is a general schematic: http://www.zamacarb.com/carburetors/431

Sounds like the needle is stuck open. Could be the spring under the needle lever has failed and needle doesn't stay seated until pressure is applied to lever by the metering diaphragm.

These carbs are available as AM on fleabay for $15. When they are that cheap, I don't bother with a $10 rebuild kit.
Click to expand...


Thanks Doug . I found a few you tube videos . They used zama kits to rebuild. Not a huge amount of hours on this machine. Strange how this happened, i' m getting a lot of air in the primer. Maybe the needle stuck or the diafram is leaking.
 
Zama site has good info. They say flooding is caused by the fuel tank vent open or restricted.

Where's the vent? How does the carb suck the fuel out of the tank?
 
I don't know this FS45 but normally: the crankcase has an impulse hole and it connects with the carb impulse hole - causes fuel pump diaphragm to move and suck gas out of tank. Guessing that fuel tank vent is in the fuel tank cap or a duckbill valve.
 
Take your air filter out and spray it with carb cleaner let dry and see what happens.
 
Just reread your post you had upside down that's when the filter loads up with fuel and oil and that my freind is when it will not start.
Clean that filter it is like having the choke on full.
 
I pulled the gas soaked filter out, but there was still gas running out.

Bret thanks for the tech manual. I couldn't find that. Stihl must have them locked up somewhere.

It's up in the cabin so I won't get to work on it until the weekend.
 
Also check your spark arrestor in your muffler. They screw out with a ratchet and socket. The are notorious for gettin clogged. Then you have 3 options. Clean, get a new one or cut the screen off, that is what I do anyways. It saves $15
 
Solved!
To recap , I could not even get a burp of running trying to start this. There was spark, and gas everywhere. Pull , pull, gas spitting out the muffler.

I took the cab apart and cleaned. Now the I get the typical stilh burp. But no way will it run more than 1/2 second.

Must be a carb issue. Doug great advice, amazon $22.

Put the new carb on. A few pulls and the same 1/2 second of running.

Duramaxman, you are the man. Thought you said it was the cat you cut out, so I screw out the spark arrested, looking for the cat. But the spark arrested is all plugged up. I pull and it fires right up.

The tech manual barley mentions the spark arrestor, but one line does say clean it. Like the spark arrested screen on my stove had to go. The screen on the weed wacker had to go.

Wonder if my chain saw has one off these?


Thanks guys for the excellent advice.
 
Last edited:
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xman23 said:
Wonder if my chain saw has one off these?
Click to expand...
Yeah, most newer 2 cycles will have a spark arrestor screen. Carb cleaner and a wire brush will make them new. Good that trimmer is working.
 
I've never used the carb cleaner & brush method, but I clean spark arrestors with a flame. You can use a torch like in the video below, but I've found that even one of those "windproof" grill lighters will get the thin screen red hot. Keep hitting it with the flame until all the crud and carbon is consumed.

 
Generally you dont have many spark arrestor problems in chainsaws because you are running them wide open and the are running hotter to burn all the gas and oil. Unless you are running a poor grade of gas and oil. Trimmers usually dont get run wide open all the time. Glad you got it fixed.
 
I cleaned it with the wood stove glass cleaner. But I do like the torch idea.
 
I thought that was the end , but no. I start weed wacken and it starves for gas and dies.

I recall reading that the carb won't work unless the fuel tank is vented to the outside air. no difference in air pressure. I took the tank cap off and run it under load and it's perfect.

To do this in the past it used to.be a pin hole in the gas cap somewhere. Not STHIL. They must have a whole engineering department just for gas caps. I own the famous flip cap on the saw, and this one. The most engineered caps I have every seen.

This has three different sections, two ceramic porous disks and a rubber valve. The disks seem pretty pluged. I cleaned them, but left the bottom one out.

Runs perfect. Used a half a tank of gas

All this happened from the engine being upside down for a while.
 
Last edited:
xman23 said:
Solved!
To recap , I could not even get a burp of running trying to start this. There was spark, and gas everywhere. Pull , pull, gas spitting out the muffler.

I took the cab apart and cleaned. Now the I get the typical stilh burp. But no way will it run more than 1/2 second.

Must be a carb issue. Doug great advice, amazon $22.

Put the new carb on. A few pulls and the same 1/2 second of running.

Duramaxman, you are the man. Thought you said it was the cat you cut out, so I screw out the spark arrested, looking for the cat. But the spark arrested is all plugged up. I pull and it fires right up.

The tech manual barley mentions the spark arrestor, but one line does say clean it. Like the spark arrested screen on my stove had to go. The screen on the weed wacker had to go.

Wonder if my chain saw has one off these?

Thanks guys for the excellent advice.
Click to expand...
 
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