Fs 91 r won’t start

[Garrettarsen00]

Weedeating a back yard when it dies on me due to running out of gas, so I go over there and fill it up and go to start it and now it doesn’t wanna turn on, this was 3 days ago and I have tried 2 times since then and it will start up first time and die after a few seconds and not turn back on. Used the same gas mixture but if I didn’t and went from 40:60 to 50:50 could that cause my issue?

 

[StarTech]

First I hope you weren't using either 40% oil to 60% gas or 50% oil to 50% gas. As you should had been using 40 to 1 / 50 to 1 mix ratios which are 40 parts gas to 1 part oil / 50 parts gas to 1 part oil. Basically that is either 40/50 ounces to 1 ounce. Here I use a multi mix synthetic oil that is good in anything that requires 16:1 up to 50:1. It actually mixes at 50:1 (2.6 ounces of oil to one gallon.) Now of course this is based on US liquid measurements.

These FS91's are four cycle hybrid engines (4 mix engines) (4140) and are fairly expensive to replace. I would highly recommend you carry it to a shop that knows what they are doing. But you can check the muffler spark arrester for clogging as these are known for these to clog especially when a 40:1 mix is used. The difference between the 40;1 and 50:1 when synthetic fuel oils are used will not cause a problem than the 40:1 will tend to clog the spark arrester quicker.

Other than that it can be the valves out adjustment, carburetor problems, or internal engine problems. An experienced tech will know how to properly diagnose the problem and repair it quickly. We have the appropriate non invasive test tools on hand and the experience of how these breasts can act up.

But if you feel comfortable troubleshooting the problem and have deep pockets we can try to walk you through the some of the basic troubleshooting.

 

[Garrettarsen00]

First I hope you weren't using either 40% oil to 60% gas or 50% oil to 50% gas. As you should had been using 40 to 1 / 50 to 1 mix ratios which are 40 parts gas to 1 part oil / 50 parts gas to 1 part oil. Basically that is either 40/50 ounces to 1 ounce. Here I use a multi mix synthetic oil that is good in anything that requires 16:1 up to 50:1. It actually mixes at 50:1 (2.6 ounces of oil to one gallon.) Now of course this is based on US liquid measurements.

These FS91's are four cycle hybrid engines (4 mix engines) (4140) and are fairly expensive to replace. I would highly recommend you carry it to a shop that knows what they are doing. But you can check the muffler spark arrester for clogging as these are known for these to clog especially when a 40:1 mix is used. The difference between the 40;1 and 50:1 when synthetic fuel oils are used will not cause a problem than the 40:1 will tend to clog the spark arrester quicker.

Other than that it can be the valves out adjustment, carburetor problems, or internal engine problems. An experienced tech will know how to properly diagnose the problem and repair it quickly. We have the appropriate non invasive test tools on hand and the experience of how these breasts can act up.

But if you feel comfortable troubleshooting the problem and have deep pockets we can try to walk you through the some of the basic troubleshooting.

It can’t be that bad where I need a shop to do something to it. I’m good with trouble shooting it. But I just put the wrong mixture in it. I really thought it was a 2 stroke idk how I messed up that bad. I thought my old mixture was a 40:60 so I made a new one but i guess it was 40:1.

 

[slomo]

I would dump all that Wesson Oil out that you put in. Flush the tank out with regular unleaded fuel. Flush it out again. Get all that oil out. Probably have to spray something into the carb to get it to fire off.

Download the manual for that machine. Read it a couple times. Read it again. Follow what is says to the letter.

 

[Garrettarsen00]

I would dump all that Wesson Oil out that you put in. Flush the tank out with regular unleaded fuel. Flush it out again. Get all that oil out. Probably have to spray something into the carb to get it to fire off.

Download the manual for that machine. Read it a couple times. Read it again. Follow what is says to the letter.

Man I’ve read the Manual it was a simple mistake, all my other weed eaters were 50/50 mixes and it just completely left my mind. How do I go about flushing it out?

 

[slomo]

Okay, we all have to start some place. I'm with ya' dog.

You meant to say 50:1. 50 parts fuel to ONE part oil.

Take fresh unleaded. Pour it INTO the fuel tank. Put the cap on. Shake it up, swirl it around. Dump it out. Get the tank clean as a new one. LOOK inside, make sure it's clean. Used compressed air and blow it out.

 

[Garrettarsen00]

Okay, we all have to start some place. I'm with ya' dog.

You meant to say 50:1. 50 parts fuel to ONE part oil.

Take fresh unleaded. Pour it INTO the fuel tank. Put the cap on. Shake it up, swirl it around. Dump it out. Get the tank clean as a new one. LOOK inside, make sure it's clean. Used compressed air and blow it out.

Do that a couple of times then make sure I put the right stuff in there and then try again?

 

[slomo]

Do that a couple of times then make sure I put the right stuff in there and then try again?

Sure. Clean the tank out, put in fresh fuel. Yank the cord.

 

[Tiger Small Engine]

Sure. Clean the tank out, put in fresh fuel. Yank the cord.

There is no equipment that runs on 50% fuel and 50% oil. The Stihl FS91 is a 4-mix, meaning it is a 4-stroke that has no crankcase for oil. It has valves (unlike a 2-stroke). I have noticed in life that people sometimes have a difficult time in life listening. Listening is a learned skill that I have improved on over the years.

 

[StarTech]

The problem is the OP has his terms wrong. He has the normal fuel mixes of 40:1 and 50:1. The FS91 will run on both fine. I use modern fuel oil (multi-mix) mixed at 50:1 in about everything.

I tried to get him to check the spark arrester in the muffler as they tend to clog using 40:1 mix as Stihl tends to run their equipment on the rich side.

Item #2 is the spark arrester screen that need removing,cleaned, and reinstalled.

Yes the 4-Mix engine confuses a lot of people when I ask have you checked the valve adjustment as they think it is a normal 2 cycle. It is not, it is a hybrid 4 cycle engine that uses 2 cycle fuel mix to lube the crankcase as normal 2 cycles do. A very good design overall.