Stihl FS94R hard start. Ideas before carb replacement?

[brokeasajoke]

So as the title says, I have a roughly 3 year old FS94R stihl 2stroke trimmer that all of a sudden became troublesome to start. A touch of anything flammable on the air filter and it will fire right up and continue to start well warm, with one pull. Trimmer runs great once running. Just a starting problem not a running problem. I pulled the carb apart with the exception of the jet screws and cleaned it. Sounds like low compression problem but the age of the trimmer makes me raise an eyebrow to low compression. I've never run it without an air filter and always use ethanol free gas always mixed 50:1 or high 40s:1. My compression gauge has seem to went on a vacation somewhere. Up for any ideas before I drop $60 on a new carb which I don't care to do if I know it would solve the problem. Thanks.

 

[Roadworthy]

If you've not already done so you could try replacing the fuel filter. It's inside the tank and accessed by pulling that big rubber plug where the fuel line exits the tank.

 

[brokeasajoke]

Carb has the bubble and primes well for what ever that's worth.

 

[newbury]

Try running something like Seafoam through it.

 

[brokeasajoke]

Local dealer has carbs for 44.99 plus tax so I ordered one.

 

[xrjohndeere]

So as the title says, I have a roughly 3 year old FS94R stihl 2stroke trimmer that all of a sudden became troublesome to start. A touch of anything flammable on the air filter and it will fire right up and continue to start well warm, with one pull. Trimmer runs great once running. Just a starting problem not a running problem. I pulled the carb apart with the exception of the jet screws and cleaned it. Sounds like low compression problem but the age of the trimmer makes me raise an eyebrow to low compression. I've never run it without an air filter and always use ethanol free gas always mixed 50:1 or high 40s:1. My compression gauge has seem to went on a vacation somewhere. Up for any ideas before I drop $60 on a new carb which I don't care to do if I know it would solve the problem. Thanks.

Take the carb apart and see if there is a gunky film on the inside? You can scrape it and it looks like plastic. I had a Stihl weed eater that I had the dealer repair the carb every year because of the exact symptoms. He took the carb apart and showed me this film. He said it was a common problem. Something they put on the aluminum during manufacturing in China. It comes loose and plugs up the jets.

 

[jaxs]

Let us know if new carb solve's the problem.
On a side note. When I bought my Husqvarna trimmer and saw they offered additional 3 years warranty if I bought 3 quarts of their pre-mix for each. I continued using pre-mix and both started and ran perfect for over 4 years,,,,,,then my son borrowed the saw. After I went to his house and retrieved it,the engine bogged each time throttle was pressed. True to their promise,the dealer fixed it under warranty. The tech told me the carb looked to had poor fuel ran through it and said he woudn't run pump gas if it was free. I realize this debate has gone on for years but I look at it like this. If mfgr is that generous with warranty and confident enough a consumer will be convinced and continue after using 3 quarts,they should know better than shade trees.

 

[brokeasajoke]

Take the carb apart and see if there is a gunky film on the inside? You can scrape it and it looks like plastic. I had a Stihl weed eater that I had the dealer repair the carb every year because of the exact symptoms. He took the carb apart and showed me this film. He said it was a common problem. Something they put on the aluminum during manufacturing in China. It comes loose and plugs up

Let us know if new carb solve's the problem.
On a side note. When I bought my Husqvarna trimmer and saw they offered additional 3 years warranty if I bought 3 quarts of their pre-mix for each. I continued using pre-mix and both started and ran perfect for over 4 years,,,,,,then my son borrowed the saw. After I went to his house and retrieved it,the engine bogged each time throttle was pressed. True to their promise,the dealer fixed it under warranty. The tech told me the carb looked to had poor fuel ran through it and said he woudn't run pump gas if it was free. I realize this debate has gone on for years but I look at it like this. If mfgr is that generous with warranty and confident enough a consumer will be convinced and continue after using 3 quarts,they should know better than shade trees.

I took the carb apart and cleaned wit brake cleaner and sprayed all holes. I always run ethanol free fuel and clear out the gas nozzle hose into truck or mower first. Always use stihl ultra silver bottle. Once it starts it runs great.

 

[xrjohndeere]

I took the carb apart and cleaned wit brake cleaner and sprayed all holes. I always run ethanol free fuel and clear out the gas nozzle hose into truck or mower first. Always use stihl ultra silver bottle. Once it starts it runs great.

That is exactly how mine was. I ended up replacing the carb with a new one and that I believe fixed it. I was so ticked off at it I gave it to my nephew. He said it starts and runs like a champ. Go figure. I went and bought a 4 cycle Husqvarna. No mix gas. Starts very easy and quiet. I also have a Ego battery powered weed eater. I like it better than any others I have had. Squeeze the trigger and go. Good luck. It can be frustrating.

 

[brokeasajoke]

New carb new plug same symptom. Carb was pretty well set from the factory though. Idles good and seemd to be about right wide open. Had to give it a snuff of brake cleaner to get it going though just like before.

 

[Richard001]

Does the engine have a primer bulb ? If so, and after using that, it still will not start, then I suspect that the fuel line are not routed correctly.

 

[brokeasajoke]

Yes it does and I'm pretty sure I put them correct but it's as easy as finding needle nose pliers to find out

 

[newbury]

Did you check the impulse line?

 

[brokeasajoke]

Did you check the impulse line?

What do I look for? It primes well with the bubble.

 

[Richard001]

From here:

Carb Cleaner vs Brake Cleaner | What's the Difference? | PJ1 Powersports

Find out make makes brake cleaner and carburetor cleaner unique and when to use each to get your parts clean without damaging other components!

pj1.com

July 27, 2020 at 10:06 pm
I sprayed brake cleaner on the outside of the carburetor on my Stihl FS 55 R weed eater and, it never ran correctly again. I adjusted it and got it running a bit better, but, after it set a few days it would not start again. I replaced the carburetor before it would start and, run correctly. Any idea what happened?

Reply
BlueDevil Pro says:
November 6, 2020 at 1:27 pm
Jack,

Thanks for your question about your Stihl Weed Eater. Sometimes if your carburetor has any sort of debris or build up inside trying to clean it can actually end up clogging it. This is especially true in a small engine carburetor like you’re talking about because the air and fuel passages are so incredibly tiny it is very easy for them to get clogged from debris or gunk.

Thanks again for your question!

Reply
johnny stecchino says:
January 4, 2021 at 8:58 pm
chances are that there was a plastic jet or nozzle and it was destroyed by the brake cleaner. brake cleaners destroy plastic or rubber parts. brake cleaner should only be used on metal parts or brakes. brake cleaner is a very powerful cleaner/degreaser and it easily dissolves organic compounds and oils.

carb cleaner is designed to clean carbs with plastic jets, it is designed not to destroy plastic parts or wash away “oils”. it does dissolve gas that’s turned into “varnish” or dried up gas. it leaves plastic jets intact and does not leach out the oily plasticizer in plastic parts. once that is leached out, the plastic goes brittle and breaks up.

lesson: use the products as intended! or else you are taking a chance – you don’t know what they are really designed to do or how they do it and then you get the surprise.


I think you are making a big mistake using brake cleaner on your carb.

 

[Richard001]

From here:

Carb Cleaner vs Brake Cleaner | What's the Difference? | PJ1 Powersports

Find out make makes brake cleaner and carburetor cleaner unique and when to use each to get your parts clean without damaging other components!

pj1.com

July 27, 2020 at 10:06 pm
I sprayed brake cleaner on the outside of the carburetor on my Stihl FS 55 R weed eater and, it never ran correctly again. I adjusted it and got it running a bit better, but, after it set a few days it would not start again. I replaced the carburetor before it would start and, run correctly. Any idea what happened?

Reply
BlueDevil Pro says:
November 6, 2020 at 1:27 pm
Jack,

Thanks for your question about your Stihl Weed Eater. Sometimes if your carburetor has any sort of debris or build up inside trying to clean it can actually end up clogging it. This is especially true in a small engine carburetor like you’re talking about because the air and fuel passages are so incredibly tiny it is very easy for them to get clogged from debris or gunk.

Thanks again for your question!

Reply
johnny stecchino says:
January 4, 2021 at 8:58 pm
chances are that there was a plastic jet or nozzle and it was destroyed by the brake cleaner. brake cleaners destroy plastic or rubber parts. brake cleaner should only be used on metal parts or brakes. brake cleaner is a very powerful cleaner/degreaser and it easily dissolves organic compounds and oils.

carb cleaner is designed to clean carbs with plastic jets, it is designed not to destroy plastic parts or wash away “oils”. it does dissolve gas that’s turned into “varnish” or dried up gas. it leaves plastic jets intact and does not leach out the oily plasticizer in plastic parts. once that is leached out, the plastic goes brittle and breaks up.

lesson: use the products as intended! or else you are taking a chance – you don’t know what they are really designed to do or how they do it and then you get the surprise.


I think that you are making a big mistake by using brake cleaner on your carb.

 

[brokeasajoke]

From here:

Carb Cleaner vs Brake Cleaner | What's the Difference? | PJ1 Powersports

Find out make makes brake cleaner and carburetor cleaner unique and when to use each to get your parts clean without damaging other components!

pj1.com

July 27, 2020 at 10:06 pm
I sprayed brake cleaner on the outside of the carburetor on my Stihl FS 55 R weed eater and, it never ran correctly again. I adjusted it and got it running a bit better, but, after it set a few days it would not start again. I replaced the carburetor before it would start and, run correctly. Any idea what happened?

Reply
BlueDevil Pro says:
November 6, 2020 at 1:27 pm
Jack,

Thanks for your question about your Stihl Weed Eater. Sometimes if your carburetor has any sort of debris or build up inside trying to clean it can actually end up clogging it. This is especially true in a small engine carburetor like you’re talking about because the air and fuel passages are so incredibly tiny it is very easy for them to get clogged from debris or gunk.

Thanks again for your question!

Reply
johnny stecchino says:
January 4, 2021 at 8:58 pm
chances are that there was a plastic jet or nozzle and it was destroyed by the brake cleaner. brake cleaners destroy plastic or rubber parts. brake cleaner should only be used on metal parts or brakes. brake cleaner is a very powerful cleaner/degreaser and it easily dissolves organic compounds and oils.

carb cleaner is designed to clean carbs with plastic jets, it is designed not to destroy plastic parts or wash away “oils”. it does dissolve gas that’s turned into “varnish” or dried up gas. it leaves plastic jets intact and does not leach out the oily plasticizer in plastic parts. once that is leached out, the plastic goes brittle and breaks up.

lesson: use the products as intended! or else you are taking a chance – you don’t know what they are really designed to do or how they do it and then you get the surprise.


I think that you are making a big mistake by using brake cleaner on your carb.

Good point. My cleaner is acetone based and doesn't play well with ABS especially in large doses. Brand new Stihl brand carb giving same symptoms. I did check the lines. Switched them and tried to prime but of course wouldn't prime. Switched back primed carb and fired up with one pull! What the heck. Went out a few hours later and it took about 5 pulls and started. Gonna let completely cool till tomorrow and try again.

 

[Richard001]

Does your carb look like this with only two line going to it ?

If it is, in this video the guy says that the bulb pressurises the fuel tank. If the fuel tank cover does not seal the opening to be air tight, or of the one way valve in the cap is malfunctioning, then you will never pressures the tank and thus no priming.

Richard

 

[brokeasajoke]

Does your carb look like this with only two line going to it ?

View attachment 739816

If it is, in this video the guy says that the bulb pressurises the fuel tank. If the fuel tank cover does not seal the opening to be air tight, or of the one way valve in the cap is malfunctioning, then you will never pressures the tank and thus no priming.

Richard

It's a little different. Tank gets pressurized. When I pulled line off carb fuel came out until pressure stabilized. I get the pssst when opening the cap as well. Primer bubble primes great.

 

[brokeasajoke]

So my Husqvarna 525LST started doing the same thing. Dumped the gas from both pushed bubble to clear carb on both and filled up with different gas. Pow, 2 pulls. Never got bad gas in my life and it may not be but that's what it looks like. Seems if it would run it would start.