STIHL FS 45 Won't Start

[amadago]

Hi All -

New to this forum, but saw some posts related to this topic specifically.

In general, my problem is that the weed eater will no longer start.

Background
Things were running fine for the past few years, and including a half of dozen times this year.

What Happened
1. Two years ago, someone adjusted the (H, L and LA screws) because it wasn't starting. It ran fine after that.
2. Two weeks ago, I tried adjusting them back because, at idle, the string was spinning too fast and I wanted to dial it back.
3. I also added a new gas mixture - but I did double check the oil/gas mixture - it is one oil container for 2.5 Gallons, which is what I mixed.

What I've Tried
1. I've read about the screen in the exhaust being an issue - I took it out, and used my torch to burn all the carbon off of it.
2. I changed the spark plug
3. I pull the carb and looked for any dirt, anomalies, etc. - I didn't see anything, I sprayed some carb cleaner in it, but admittedly I'm not a carb expert
4. When I pulled the spark plug, I saw a lot of carbon build up on the piston, so I lightly scraped that off with a towel/screwdriver to make sure combustion could actually happen.

What I Think
1. Spark - seems unlikely that a spark is not happening. It was running 2 weeks ago, and I had been using it this year.
2. Gas Mix - I wondering more & more if it's related to that. Even when I changed the screw settings, it was at least running. It was just either bogging down on throttle, or shutting off when I let off the trigger.
3. Fuel Line - I see gas fly out of the muffler when I initially pull, so that leads me to believe it's getting gas all the way through the system.

Anyway, tried to make this as organized as possible. I'm interested in any / all thoughts you may have.
Best,
Mike

 

[waylonJ]

Hi Mike - I doubt that a bad gas mix would prevent the device from starting. Unless it was really off. My guess is the carb on this. There is likely a diaphragm in the carb which get's stiff and does not function. I would suggest you first see if you can find a new cheap carb and start with that - it should fix the issue. If the carb is expensive (more than $30) I would look into a rebuild kit and find a video. Steves Small Engine Saloon is a great channel to look at on YouTube.

 

[amadago]

Waylonj -

Thanks. I've actually been to his YouTube channel. I've read about the diaphragm, but didn't really know what it was or why it would suddenly go bad.
Update - it was $16 on Amazon for the rebuild kit, so I just bought one and we'll see how it goes. Just would be surprising that it was running, and then not all of the sudden.

 

[PTmowerMech]

Depending on where you live, and the shops around you, I can't see many shops rebuilding your carb (with OEM kit) and getting it back to running for you, for more than $50 to $75. I charge $35 plus the kit at my shop. And the carbs get cleaned out very well with OEM (or equal) kit. Then reinstalled and adjusted. So when the customer gets it back it's ready to to.

 

[amadago]

Thanks PTmowerMech. I've done very little carb work in my lifetime, but I'm going to give this a try and see what I can do. There's a good chance this ends up at the Stihl dealership down the road when I'm done still.

 

[PTmowerMech]

Thanks PTmowerMech. I've done very little carb work in my lifetime, but I'm going to give this a try and see what I can do. There's a good chance this ends up at the Stihl dealership down the road when I'm done still.

The reason I say that, mainly is because of the metering level that needs t be done. If the straight edge is all you need, then you'll probably be OK.

 

[StarTech]

One question will it even hit with induced fuel mix into the cylinder?

If carburetor problems when it goes to the Stihl dealer most likely they will just replace the carburetor. Shop like PT's and mine rather repair the current carburetor when we can but when Stihl acquired a controlling share in Zama (which the IPL indicates you got a version of the C1Q carburetor) getting a carburetor repair is nearly impossible now, even the dealers have a hard time getting them. Sometimes shops like mine can piece together a repair kit from individual parts just of our experience.

 

[amadago]

@StarTech sorry, what do you mean when you say "will it even hit..."?? If that means - does it seems like it's going to turn over, but doesn't, the answer is no. At no point does it seem like it's going to start up. When I pull it, it just kicks some fuel out of the exhaust the first time (assuming that's just happening after priming it), and then nothing really happens.

 

[StarTech]

That "HIT" mean iginites the fuel while under compression.

Sound like a loss of compression or timing problem. It is more likely that the compression is below 100 psi. Pull (remove) the muffler and take a look at the piston and ring(s). If the piston is scored or the piston ring is stuck, that would the reason for lack of proper compression.

 

[amadago]

thanks @StarTech. I'll check that. I feel like if that's the case - time for a new weed wacker? It's not old-old, but it's 8yrs old still.