Stihl gas trimmer problem.


  #1  
Old 04-29-19, 01:52 PM
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Stihl gas trimmer problem.

I have a Stihl FS 70RC gas trimmer. I believe I bought it in 2012. It gets very light use...and has never had any issues starting (other than the first start of the season where I swear I am never buying a gas trimmer again. ) Anyway...I used it last weekend, started after a few pulls, and worked fine. This weekend...it was tough to start, and once it did, it was tough to keep it going.

Once it ran a few minutes, it would start to sputter...and I had to keep the gas pressed to keep it from dying. So the idle would not work, essentially. And then after it died, or if I cut it off...I could not get it to warm-start. I have to let it cool completely down...and then do a cold start. Of course once I do that...I have to make sure I keep giving it gas so it doesn't cut out. It doesn't make sense to me that a $300 machine is this freaking difficult to get to run. I took the carb cover off, and the air filter looks brand new...I mean this thing really only gets used a few times a year. The one thing that I notice is that there is a good smattering of oil...in that compartment on the back ( I don't know what it is...it's an opening of sorts...and there is a lot of oil spatter there).

I bought some fresh gas and plan on refilling it tonight to see if that makes a difference. If it does, I'll post that here.
But just wanted to see if the behavior rang any bells with anyone.
 
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Old 04-29-19, 03:29 PM
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Always start the season with fresh gas/oil mix and an ounce of Sea Foam if you've neglected the gas in it.. Use the best gas and oil you can find and avoid ethanol. Also empty the fuel out of it at the end of the season and run the carb dry.

Is your primer purge bulb working? Cycle that about five times to clear out air bubbles.

If you change trimmers go to an Echo 225.
 
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Old 04-29-19, 03:45 PM
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I am willing to bet that it is not the machine's fault. Fuel, fuel, fuel is what I think is the most common cause of small engine problems. Taking off the air cleaner cover won't tell you anything. It's what auto gas does when sitting for long periods in the tiny passages and orifices of a tiny carburetor that causes the problems. The tiny carburetors have really tiny internal passages and jets and it doesn't take much to get clogged or blocked.

What's done is done but if you use your tool infrequently I strongly suggest using Avgas (aircraft gas) or one of the canned gasses intended for small engines. Using a tool infrequently makes fuel care even more important. Aviation gas and some "canned fuels" are much more highly refined than auto gas and do not varnish or gunk up like auto gasoline can.

Buying fresh gas now probably won't help but you could get lucky. If it doesn't resolve the problem you may need to remove, disassemble and thoroughly clean the carburetor. It also wouldn't hurt to rinse out the fuel tank and fuel lines to make sure they are also clean. It's not a difficult job just make sure you take lots of pictures along the way so you can put everything back together properly.
 
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Old 04-29-19, 04:29 PM
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Aviation gas and some "canned fuels" are much more highly refined than auto gas and do not varnish or gunk up like auto gasoline can.

Cant dispute that this is an option, but if everybody would just run stabil gas treatment in the machine for 4 min at the end of the season the small gas engines will fire right up 5 months later when the season begins!

Forget once, you may be out of luck, let it sit for a full year, your in trouble!
 
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Old 04-29-19, 04:48 PM
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I 100% Agree it's likely a fuel issue, but disagree with how to deal with it.
If it's Stihi you had to have bought it from a dealer, with such low use you should have been buying there premixed fuel that is non ethanol gas with a fuel stabilizer in it.
There's 0 reason to be buying aviation gas!
There's thousands of gas stations selling non ethanol gas.
Good luck trying to pull apart that tiny Carb. and cleaning it.
I just buy a new one on Ebay that includes a new air filter, spark plug, gaskets, tank filter for $13.00. Dealer wanted $39.00 for just the carb.
At the end of the season I do as suggested, dump out the left over fuel and run it until it stops.
Season begins, add new fuel starts up second pull every time.
 
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Old 04-29-19, 08:19 PM
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"Is your primer purge bulb working? Cycle that about five times to clear out air bubbles."

Yup primer bulb is in great shape. I definitely did the five times.


For what it's worth, I rebuilt the carburetor on my Echo blower a few years ago. So I could take it apart if I had to...but I sure don't want to. It's a PITA and I just don't have much time to spend on it.

I didn't get the fuel into it yet, but hopefully will be able to try it tomorrow night (BF is coming up so maybe I can sweet-talk him into looking at it LOL).


I am familiar with Stabil, and have used it before. If I get the thing working again I might pick some up. But I should slap myself on the fuel. I actually have a small can of TrueFuel...but I had stashed it in the cabinet and completely forgot what the heck I bought it for.

If I can't get it to start, then I'll try buying a new carb and see if I can put it on (had no idea I could get one on eBay - DUH). And then I WILL be using the canned fuel in the future.
 

Last edited by yardnut; 04-29-19 at 08:52 PM.
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Old 05-01-19, 07:41 AM
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Well I bought some Mechanic-in-a-bottle after reading all the rave reviews. Put in 2 ounces and let it sit a few minutes. But no change. BF is actually astounded that this thing won't start - he said he has had a Stihl for years, does pretty much nothing to it, maintenance-wise, and it starts every time. I guess 2-cycle gas engines and me, just don't mix.


I called the dealer closet to me, and they said that they have to send the carburetors off for service! I did find one dealer - not really close to me - that sells the replacement carbs but she couldn't give me a price unless I had the exact model number of the carb (which I don't). She said probably between $30-$50.

So, I looked on eBay and ordered this:

https://www.ebay.com/itm/153069574742

Should be here in a few days, so guess I get to replace a carburetor LOL. Should be easier than rebuilding though. I sure hope it works.
 
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Old 05-01-19, 08:13 AM
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What did you do with the Mechanic in a Bottle? Did you just put it in the tank?

You would need to get it mixed thoroughly, then cycle the primer bulb about five times. Then with the choke on full and no throttle, spin the engine over about five times to get the fuel/cleaner into the carb and circuits.

Let that sit half an hour, take out the plug and spin the engine with full throttle, no choke, to purge the combustion chamber. Then stick the plug back in it and try to start it with normal starting procedures.

Once you get it going you should be able to start it with just a couple pulls if you take care of the fuel. If you don't you may as well buy a dozen carburetors.
 

Last edited by marbobj; 05-01-19 at 08:33 AM.
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Old 05-01-19, 08:39 AM
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If it's Stihl you had to have bought it from a dealer, with such low use you should have been buying there premixed fuel that is non ethanol gas with a fuel stabilizer in it.
I've had Stihl products before but never heard this but I wont buy Stihl again, you have to go to the dealer for parts, too expensive!

So, I looked on eBay and ordered this:
Just be aware, these are cheap, I mean really cheap China made crap, I have found them to be close to useless!
 
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Old 05-01-19, 08:51 AM
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"What did you do with the Mechanic in a Bottle? Did you just put it in the tank?"

I followed the instructions on the bottle. Yes I "just put it in the tank". And primed...and pulled....many times.

"You would need to get it mixed thoroughly, then cycle the primer bulb about five times. Then with the choke on full and no throttle, spin the engine over about five times to get the fuel/cleaner into the carb and circuits."

Mixed thoroughly, with what? The instructions said nothing about mixing it with anything. After we had no success with just the additive, we did add fresh fuel. And that made no difference either. I just went out and tried it again (I took today off from work) and same result. I can prime 10 times and pull 20...and it will NOT start.

"Let that sit half an hour, take out the plug and spin the engine with full throttle, no choke, to purge the combustion chamber. Then stick the plug back in it and try to start it with normal starting procedures."

What "plug" are you referring to? None of what you are saying is on the instructions.

"Once you get it going you should be able to start it with just a couple pulls if you take care of the fuel."

Pretty sure I already stated that in a previous post.
 
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Old 05-01-19, 08:54 AM
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"Just be aware, these are cheap, I mean really cheap China made crap, I have found them to be close to useless!"

I purchased it because it was recommended in one of the replies here. So now you tell me they are crap? Great.
 

Last edited by yardnut; 05-01-19 at 09:18 AM.
  #12  
Old 05-01-19, 09:13 AM
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UPDATE!
So I just went out and tried again...and it started! I let it run...it cut off...I started it again...and let it sit there with the choke on, and let it run for maybe 1 minute. Picked it up and used it for about 2 minutes...and then it started doing the same thing...sputtering when I gave it gas...and then it cut off. Started it again...same thing. Used if for a minute but it cut off when I gave it gas. Now it doesn't want to start...but honestly I am over it for the moment.
So..any thoughts on THIS behavior? Could it be some other issue?
 
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Old 05-01-19, 10:01 AM
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Plug = spark plug
Mix thoroughly with the gas in the tank = just shake it after you add it to the tank.

The primer does not prime the engine, it just primes the fuel system so the choke can be effective when starting.

Right now you likely have the engine flooded. It won't start if you pull the cord 100 times.

Do this:

Dump all the gas out of the gas tank.
Put the choke on full and leave the throttle closed.
Pull the start cord ten times to turn the engine over. This gets all the gas out of the carburetor..
At this point you have a flooded engine with the fuel removed from everything before the crankcase. You need to purge the fuel from the crankcase and combustion chamber.
Take out the spark plug and place the spark plug wire away from anything it may ground on and create a spark to avoid a fire hazard.
Hold the throttle fully open and spin the engine over ten times.
Add a half spoon of fuel/oil mix down the spark plug hole and reinstall the spark plug.

At this point you have manually replaced the carburetor (roughly)

With full throttle and no choke, see if it will try to start. You'll have to pull it a few times to get the fuel you added to reduce to a combustible mixture. Each pull moves it closer. When it tries to start it will sputter and die.

Now add fuel back to the tank and cycle the primer a few times after you see the bulb full of gas. At that point the carb will be free of air and filled with fuel.

Now use normal starting procedures. If it doesn't start right off, take the choke off.

That usually gets a two stroke going.
 
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Old 05-01-19, 10:12 AM
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So..any thoughts on THIS behavior? Could it be some other issue?
No - it's fuel...............................................
 
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Old 05-01-19, 11:09 AM
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Update again! I guess it just needed more time to sit. I was working in the yard digging up a stump...and went back to the trimmer and tried again. Started, and this time, it didn't sputter or cut off. I'll be dumping the fuel and replacing it with the canned stuff tonight. Yay!!


But just to educate myself...

"Put the choke on full and leave the throttle closed."

Okay, I know what the choke is. It's that little orange switch that has a cold start and a warm start position. What is the throttle? Do you mean the lever/trigger handle that is used to give it gas?? If so....what does "leave it closed" mean?

Sorry - I know I probably sound dumb to you....but I don't work on this stuff normally. I only know about the carb because I just got fed up with my blower a few years ago and decided to try rebuilding it.
 
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Old 05-01-19, 12:58 PM
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No problem. We all have things we know and things that are a little foreign. Sounds like you're a good hands on little lady so catching on is easy for you.

Pretty sure what you have is a gummed up carb. The little passages in it that carry fuel are blocked. The longer the cleaner (Mechanics helper) is in contact with the gum, the more it dissolves and the better everything works. Today's fuel separates quickly without things like Stabil put in it.

The choke is a separate circuit that carries extra fuel for cold starting. The engine needs that when cold. After it's warmed up it runs on the normal high/low circuits and the choke isn't necessary.

Too many times when the engine isn't starting we go to the choke and over use it. Consequently the engine gets "flooded" and is a bear to start, especially 2 strokes.

The throttle you have is what you speed up the engine with, the choke is the other one you mentioned. Anytime you suspect you have over used the choke, always hold the throttle fully open and leave the choke in the off position - usually pushed in.

What you have now is the cleaner doing its job and the carb is getting cleaner. Probably, considering the quality of the machine, if you take good care of your fuel like discussed earlier, you'll have a lot fewer problems. Keep a little cleaner in the gas/oil mix for a couple tank fulls. Make absolutely sure you have the proper oil to gas ratio

If what you have now is running well, I wouldn't change carburetors. The one on your trimmer is much better than the one you bought to replace it.

We'll hope everything goes well and if you need a little help, let us know,.
 
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Old 05-01-19, 01:06 PM
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Thank you so much! Yeah that carburetor will be sitting on the shelf I guess. Oy vey.
 
 

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