Stihl FS 38 Won't start

[CaperBoi]

Can't get this trimmer started:

Took out spark plug to check to make sure there was spark and YES there is.

Looks like there's fuel getting into the cylinder because plug looked wet.

Took spark arrestor out and looked dirty and haven't put it back in yet.

Inspected air filter and didn't look to bad.

Drained fuel and put fresh mixed fuel from gas station and put a brand new spark plug.

After changing the spark plug with a new one and adding fresh fuel and keeping the spark arrestor out it still wont start. I double checked to make sure the plug has spark which it does and can pull many times with the choke on and i can see fuel spitting out of the exhaust and still not even a hint of combustion. Prior to this the last few times it seemed like the primer bulb wasn't working right as it wouldn't fill up with fuel but this time it seems like it is. When I press it down and release it, it fills up with fuel.
After a couple of times of trying and flooding the trimmer I would remove the spark plug and dry out the chamber with short bursts from a propane torch and try it again but still nothing.

 

[mechanic mark]

http://www.stihlusa.com/WebContent/...ls/STIHL-FS-38-Product-Instruction-Manual.pdf Page 20 under fuel, minimum octane rating 89, stihl 50:1 2 cycle oil mix, gap plug to specs. in manual. This is a top of the line namebrand, requires best fuel & oil mix. Read pages 27 & 38 also, correct spark plug & gap.

 

[CaperBoi]

http://www.stihlusa.com/WebContent/...ls/STIHL-FS-38-Product-Instruction-Manual.pdf Page 20 under fuel, minimum octane rating 89, stihl 50:1 2 cycle oil mix, gap plug to specs. in manual. This is a top of the line namebrand, requires best fuel & oil mix. Read pages 27 & 38 also, correct spark plug & gap.

Hey thanks for the link and info. I have been using this trimmer for almost 3 years now and have always mixed my own 50:1 with the recommended Stihl oil and fuel and even today I bought premium fuel with a higher octane rating. I doubled checked the plug gap and to make sure it was 0.02 on the old plug and the gap was off and was smaller than it was suppose to be so I regaped the plug with no success.
I only started having this problem after I started using it the other day and it started bogging down and stalling and then it wouldn't restart.

 

[smallenginemechanic]

Hey thanks for the link and info. I have been using this trimmer for almost 3 years now and have always mixed my own 50:1 with the recommended Stihl oil and fuel and even today I bought premium fuel with a higher octane rating. I doubled checked the plug gap and to make sure it was 0.02 on the old plug and the gap was off and was smaller than it was suppose to be so I regaped the plug with no success.
I only started having this problem after I started using it the other day and it started bogging down and stalling and then it wouldn't restart.

By fresh fuel i assume it was bought within the last week or so? If so you need to rebuild the carb and check the internal diaphragm and metering diaphragm if they are hard or cracked replace with a carb kit. Also make sure you blow out all small passageways with carb/brake cleaner. Make sure to remove the screen and clean it out I'm sure its clogged with debry. If that doesn't work then compression test. Should have at least 90+ psi.

 

[CaperBoi]

By fresh fuel i assume it was bought within the last week or so? If so you need to rebuild the carb and check the internal diaphragm and metering diaphragm if they are hard or cracked replace with a carb kit. Also make sure you blow out all small passageways with carb/brake cleaner. Make sure to remove the screen and clean it out I'm sure its clogged with debry. If that doesn't work then compression test. Should have at least 90+ psi.

Ya I bought new fuel this afternoon and I've got a old but good working 4 stroke Ryobi that I use as a backup so my next step is to tear down the carb and check and clean everything. I did take a peek at the piston wash and it looked fine. First thing I'll check is the compression and take it from there.

 

[CaperBoi]

Found a good Youtube video for the carburetor rebuild

 

[mechanic mark]

Page 33 in manual says to replace pick up body in fuel tank every year.

 

[CaperBoi]

Page 33 in manual says to replace pick up body in fuel tank every year.

I'm going to have a chance to stop in at a Stihl dealer tomorrow and will see if they have a carb rebuild kit and pick up but first thing in the morning I get to check the compression.

 

[CaperBoi]

I'm going to have a chance to stop in at a Stihl dealer tomorrow and will see if they have a carb rebuild kit and pick up but first thing in the morning I get to check the compression.

Well I stopped to pick up a carb kit and forgot look to at the number on the carb so couldn't get the correct parts. This morning I checked the compression and got a good solid reading of 90 PSI so I tore down the carb and fuel lines and the screened pickup and inspected everything and gave the carb a good cleaning and blew out the all passages with air and assembled everything back together and got it to fire back up and run and idle nice and smooth. I'll try it again once and awhile to see if it acts up again and gives me any problems.:smile:

 

[Fish]

Problem with the carb kits is that they are so expensive, sometimes as high as $18 or so, and you could get a new carb for @ $30. But a good cleaning usually suffices.