Need an engine wizard for this problem. Please help!

[Loco3000]

I have a one year old Stihl carburetor on my kombi that I must admit only gets used a few times a year. After sitting over winter the machine runs but will not idle. Just dies when not throttled. Have added new fuel. Running without a spark arrestor. Idle screw adjustment does nothing. Do I need to clean carb or is there an easier solution I’m not seeing?

 

[GMB74]

My KM91 does the same thing because I don't use it a lot. Find out if you need a special screwdriver to remove the mixture screws and obtain one if needed. One at a time, screw the mixture screw in until it stops. Count the number of turns. Remove the screw and carefully blow out the passage with a can of carburetor cleaner. Reinstall the screw to the original position (number of turns out from where it stops). Do the same with the other screw. See if this fixes the problem. These primer bulb carburetors seem to be very sensitive to this sort of thing and cleaning may or may not work. Using ethanol gas makes it even worse. When I worked at the dealership and we had a machine like this, we just automatically replaced the carb rather wasting time trying to clean them. They aren't (weren't) very expensive. Hope this helps.

 

[FergusonTO35]

Are you using fuel stabilizer? I've been using it more than 25 years and never had a plugged carb. My carbs need repair only when the parts are worn out. And, no I don't use non-ethanol gas.

 

[Loony661]

How do you store your machine when not in use for long periods of time?

I ask because contrary to popular belief, storing them full of fuel is actually better for them. (As long as your fuel is non-ethanol) Keeping the carb wet is better for the diaphrams and seals, and keeping the fuel tank plump-full provides the longest storage protection you can have. After all, exposure to air (oxygen) is what breaks fuel down in the first place.. Everything I own gets stored “wet” and I don’t have to clean carbs, rebuild carbs, or have any other fuel system related problems. My FS130 with the similar 4-Mix engine gets used maybe 1/2 dozen times from June-Sept. Otherwise it sits. Always fires right up. Fuel is 91 octane non-ethanol gasoline mixed 40:1.

 

[Loony661]

Oh, and welcome to the forum!

 

[Loco3000]

My KM91 does the same thing because I don't use it a lot. Find out if you need a special screwdriver to remove the mixture screws and obtain one if needed. One at a time, screw the mixture screw in until it stops. Count the number of turns. Remove the screw and carefully blow out the passage with a can of carburetor cleaner. Reinstall the screw to the original position (number of turns out from where it stops). Do the same with the other screw. See if this fixes the problem. These primer bulb carburetors seem to be very sensitive to this sort of thing and cleaning may or may not work. Using ethanol gas makes it even worse. When I worked at the dealership and we had a machine like this, we just automatically replaced the carb rather wasting time trying to clean them. They aren't (weren't) very expensive. Hope this helps.

Thank you. I will try this. I paid over 100$ for a new Stihl carb last year so I’m hoping to salvage it before getting a replacement. Only has 25 hours run time on it.

 

[Loco3000]

How do you store your machine when not in use for long periods of time?

I ask because contrary to popular belief, storing them full of fuel is actually better for them. (As long as your fuel is non-ethanol) Keeping the carb wet is better for the diaphrams and seals, and keeping the fuel tank plump-full provides the longest storage protection you can have. After all, exposure to air (oxygen) is what breaks fuel down in the first place.. Everything I own gets stored “wet” and I don’t have to clean carbs, rebuild carbs, or have any other fuel system related problems. My FS130 with the similar 4-Mix engine gets used maybe 1/2 dozen times from June-Sept. Otherwise it sits. Always fires right up. Fuel is 91 octane non-ethanol gasoline mixed 40:1.

I stored it wet but didn’t use a fuel stabilizer which might be a problem. I’m pretty sure it had supreme plus gas from chevron with no ethanol?

 

[Loco3000]

Are you using fuel stabilizer? I've been using it more than 25 years and never had a plugged carb. My carbs need repair only when the parts are worn out. And, no I don't use non-ethanol gas.

Good question. I think I need to use stabilizer going forward to prevent my current issue.

 

[Loony661]

I stored it wet but didn’t use a fuel stabilizer which might be a problem. I’m pretty sure it had supreme plus gas from chevron with no ethanol?

Most of the 2cycle oils used in the mix contain fuel stabilizers. So adding extra generally isn’t needed with good quality non-ethanol gasoline.

 

[Loco3000]

Thank you. I will try this. I paid over 100$ for a new Stihl carb last year so I’m hoping to salvage it before getting a replacement. Only has 25 hours run time on it.

I stored it wet but didn’t use a fuel stabilizer which might be a problem. I’m pretty sure it had supreme plus gas from chevron with no ethanol?

I totally understand reasoning on this and I usually store it wet. I wonder why Stihl recommends storing it away dry??

 

[Loco3000]

My KM91 does the same thing because I don't use it a lot. Find out if you need a special screwdriver to remove the mixture screws and obtain one if needed. One at a time, screw the mixture screw in until it stops. Count the number of turns. Remove the screw and carefully blow out the passage with a can of carburetor cleaner. Reinstall the screw to the original position (number of turns out from where it stops). Do the same with the other screw. See if this fixes the problem. These primer bulb carburetors seem to be very sensitive to this sort of thing and cleaning may or may not work. Using ethanol gas makes it even worse. When I worked at the dealership and we had a machine like this, we just automatically replaced the carb rather wasting time trying to clean them. They aren't (weren't) very expensive. Hope this helps.

So I tried what you suggested and it actually solved the problem but unfortunately it was only temporary. After About 10 minutes of shearing it started to stall again when not throttled. I am going to try and repeat the procedure to try and remedy. I gave 2 spray blasts in each port. Is that enough?

 

[GMB74]

Sounds like you loosened up the dried/deteriorated gas inside the carb that was causing your problem. That's a good sign. Try cleaning the jets again. Maybe you can push the gunk out and get it to run properly. As others have said, use stabilizer, it helps. Better yet, try premixed fuel like Stihl Motomix. Check out Youtube, there is a video by Steve's Small Engine Repair that explains what is in pump gas that causes these problems. Premium premix fuels like Motomix, Husqvarna XP+, etc. are manufactured without these substances that degrade and plug up your carb when it sits and dries out. Keeping your machine full (wet) with ethanol gas has its own issues with absorbing moisture and causing corrosion if it sits long enough. I have seen plenty of carbs full of silver dust from dissolved/corroded carburetor metal.

 

[FergusonTO35]

Full ounce of Sta-Bil marine formula per gallon FTW!