# Weed eater stalls when given throttle



## nate81

I have a Sithl FS85 Weed wacker that starts up after a few pulls (sometimes it takes 10-15 pulls...but it eventually starts)....It will idle just fine, nice and smooth, but when you give it gas it dies out....you can play with the gas a little...example would be to give it slow gas and let it rev up slow, but it eventually dies out. That is my problem.

Here is what i have exactly:
Stihl FS85 trimmer that has a Zama C1Q Carb.

Here is what I have done so far to fix it (nothing for me has worked yet):
New fuel filter.
New air filter.
Cleaned spark arrestor screen.
Cleaned spark plug.
New fuel lines.
I pulled the carb apart and 'wiped' it down...it did not seem very dirty anyways.
New primer bulb.


----------



## Basementgeek

Hi and welcome to the forum :wave:

Have you tried adjusting it any? Sounds like it is running to lean. Open the high speed adjustment, if possible. Many of engines have fixed adjustments.

I have a blower that is not adjustable and I find I have to keep the choke on a little, all the time.

BG


----------



## nate81

Thanks for the warm welcome 

I have not adjusted it any, as far as i know there are no adjustments I can make...i can only adjust the idle speed.


----------



## nate81

I ended up solving the problem....while in the bathroom to be exact lol


----------



## Basementgeek

Great

Now?

BG


----------



## nate81

I was in my uhm, erm.. 'office' reading the stilhl manual...and i noticed that it needs 89 octane or higher...i was running 87!! So i went and got some 89 and mixed up some oil in it...and after a few seconds to burn out the old, it runs great!!


----------



## Basementgeek

Thanks..

I have heard that before, a little better gas, but forgot about it.

BG


----------



## nate81

I'm back again....I was wrong, the weedeater still stalls on me. It runs fine for about 15-20 minutes, then when i try to give it gas it stalls out on me. Any ideas??? I really don't want to take it to the stihl shop and pay $100 to fix it!!!


----------



## Basementgeek

Hi:

Running 15-20 minutes it is OK then it stalls out, I assume you are saying the engine dies/stops.

What gas and oil mixture are you using? 50:1 probably. I think that is to little oil, my 2 cycles I use 32:1. Usually the only down side to that there is a little gray smoke and it will foul your spark plug a little sooner. Spark plugs are cheap compared to engines with to little oil.

BG


----------



## nate81

Yes, after about 15 minutes of running OK, it stops, the engine dies out. The manual calls for a 50:1 mix and thats what I'm using. Octane 93 gas as well.

You think adding a little more oil might help it run more smoothly?


----------



## SABL

Are you sure you are running a higher octane?? Most gas stations have a single pump that dispenses 3 grades of fuel from the same hose..... it probably takes a gallon to prime the hose and if you are only filling a 1 gallon can you may get a tiny bit of 93 octane. If your equipment requires higher octane, pump the first gallon into the tank of your vehicle, then fill your gas can. The fuel that is in the hose and metering system is what the previous customer purchased....probably not the premium grade you are paying for.


----------



## nate81

Extremely sensible statement SABL...I did infact purchase the gas from a single pump that dispenses all 3...I never thought of that.

Could this be the cause of all my problems? something this simple? 


btw...braveheart is one of my fav movies of all time lol


----------



## Basementgeek

Hi:

First check the manufacture and see the octane requirement is. It may not like 93, to "hot"

Next time it does dies, is it harder to pull the cord? Also need to check for spark right after is dies.

If is a lot harder to pull when it dies, that $$$$

BG


----------



## SABL

I would follow the manufacturer's guidelines for fuel but still pump a gallon or two into my vehicle to make sure I am getting the prescribed octane rating. I learned that many years ago when the single pumps came out (late 60's) from friends with motorcyles.

I'm almost as crazy as Stephen....:lol: He is my favorite character in "Braveheart".


----------



## nate81

this is from the manual that came with it...

"Use a regular branded unleaded gasoline witah a minimum octane rating of 90 RON (USA/Canada: pump octane min. 89!) If the octane number of the regular grade gasoline in your area is lower use premium unleaded fuel. Fuel with a lower octane rating may result in preignition (causing "pinging") which is accompanied by an increase in engine temperature. This, in turn, increases the risk of the piston seizure and damage to the engine"

After having read that...and changing to 93 octane, i still hear some "pinging" noises, but as SABL mentioned, i could have put mostly 87 with a little 93 in from the 'single pump theory'...which i totally agree with.

Also, to Basementgeek...after it stalls/dies out on me...i can pull the cord once (very easily) and it starts right back up, and idles like a dream. But then when given throttle, it conks out again


----------



## Basementgeek

I really lost here....

First oil is not the problem, leave it 50:1

Any chance the vent on the gas cap plugged ?

BG


----------



## nate81

I didn't realize there was a vent on the gas cap....I'll check tommorow and see whats happening.


----------



## sspenser

Would love to hear what the final resolution here was. I'm having the exact same problem, have the same carb on my Yard Man weed whacker.


----------



## K-B

On a two-stroke, shutting off after warm-up is usually one of 2 things: Either losing spark when the coil gets hot, or a plugged/defective fuel tank vent. A coil issue can easily be diagnosed by immediately checking for spark presence after the engine shuts down, as generally you will have to let it cool before it will resume sparking. A fuel problem can be diagnosed by "priming" the engine with a shot of premix gas (do NOT use ether/starting fluid on a 2-cycle engine) directly into the carb after the engine shuts down. If your issue is fuel related, it should immediately start back up, if only for a few seconds. A tank vent can easily be tested with a vac/pressure tester.


----------



## nate81

I actually got tired of not having my weed eater....(3+ months now) and bit the bullet and took it to a certified Stihl repair shop yesterday actually. I could not find a 'vent' on my gas cap....it seemed like one solid piece to me? They will be diagnosing my problem for me next week and i'll let ya know what it was  I gotta have my weedeater!!


----------



## K-B

Many premium 2 cycle engines do not have a vented cap, rather a remote tank vent. A remote vent is generally more durable and less prone to leakage.


----------



## Basementgeek

Also, I have seen a few of these small engines require something more than the regular/econo grade of gas to run good.

BG


----------



## K-B

Basementgeek said:


> Also, I have seen a few of these small engines require something more than the regular/econo grade of gas to run good.
> 
> BG


Yes. In fact, many mfg's of premium handheld equipment including Echo, Stihl, Dolmar, are now recommending to fuel with an octane rating of no less than 89. Another thing to keep in mind when purchasing higher octane fuel is to put a couple gallons in your vehicle first and then fill your can. This is because the person before you may have purchased regular gasoline, and the lines are still full of that. If you are filling a small gas can you may inadvertently be filling it with the regular gas.


----------



## nate81

Ok, so the dealer called me and said this....

my carb was bad....so its gonna cost $185 total to fix (I already gave them a $65 deposit/non refundable) and the new carb would run about $100....***??? input on this please?


----------



## Basementgeek

How old is it and now much did cost new?

BG


----------



## nate81

its like 10 years old and i'm assuming quit a few hundred dollars, it was to of the line back then and from what ive read, still is top of the line, but no longer manufactured...


----------



## Basementgeek

I guess it will be up to you to decide if it is worth it. I would not pay more than half of what it cost, in todays dollars.

BG


----------



## K-B

The FS85 sold for around $300 10 years ago and was an extremely popular model.


----------



## nate81

any input on their price of a carb? Should it cost $100?? Or could i get a carb elsewhere for much cheaper and slam it on myself? or....should i sell this weedeater as is...and buy a new one?


----------



## K-B

You can find a new carb for $50-60 online...search for Walbro WT-38
Through Stihl...I'm not surprised that it would cost $100. Generally, you figure you don't want to spend on repairs more than half of what the machine costs new, although that does depend a lot on the condition. Obviously you wouldn't want to spend $180 on a machine that has thousands of hours or has been beat up for 10 years.
If you decide to get a new one, you'd want to plan on spending at least $300 to get one similar in quality to the FS85.

EDIT:
You can get the ZAMA C1Q for around the same price...C1Q-S28D.


----------



## nate81

K-B said:


> You can find a new carb for $50-60 online...search for Walbro WT-38
> Through Stihl...I'm not surprised that it would cost $100. Generally, you figure you don't want to spend on repairs more than half of what the machine costs new, although that does depend a lot on the condition. Obviously you wouldn't want to spend $180 on a machine that has thousands of hours or has been beat up for 10 years.
> If you decide to get a new one, you'd want to plan on spending at least $300 to get one similar in quality to the FS85.


Awesome advice, i think i'm going to search and find a carb myself online and attempt to put it on myself and save about $50-$60 bucks. This weedeater is in very good cosmetic condition, it was very well taken care of, i cant see throwing it away just yet.


EDIT:
whats the difference in carbs? Should we get into that here or should i start a new thread or maybe i should just do some searching


----------



## TheAlSmith

nate81,

I am a Stihl MST and agree with all of the suggestions here so far and that what you have done is fantastic but I also think you may have overlooked something really simple here.

If your unit bogs out when you give it throttle your low speed circuit isn't getting enough fuel for the mid-range. Since you can't open the jet up as it is fixed the next question is "Did you clean the carb using an ultrasonic cleaner?" This can get the debris out of the circuits that you can't access yourself.

On a side note here, NEVER spray a 2-stroke carb with carb cleaner!!!! They have checkvalves inside that the chemicals will destroy leaving your carb a paper weight. You must use an ultrasonic cleaner and any respectable Stihl dealer will have one that you should be able to borrow for a small fee if not free.

Also, the vent in the fuel cap is often a rubber ring inside of it. If it doesn't breath properly you will have a start and stop issue as the unit can't get fuel.

I'd also like to know what the tech found was wrong with your unit so please update us.

Thanks,

Al


----------



## nate81

Thanks so much for that information TheAlSmith, it is really, really appreciated.

To answer your question about what the tech said, he said this....

my unit needs a new carb due to a 'small peice' missing from the carb....he then proceeded to show me where it was and how small it was....

I was like ..."ok, thanks"...so I am now on a mission to buy a new carb from the internet for around $50 and slap it on and i *hope* this works!! I should have my new carb in about 10 days or so from today so sometime around August 14, 2010.


----------



## nate81

So I got my new carb today, it seems to have fixed my problem  Now I need to figure out how to adjust it, it is idling wayyyy to fast, the head is spinning. Also i'm noticing a slight delay in the throttle. I can hit the gas, and there is a 1 or 2 second delay.


EDIT: I have all 3 screws turned to the right as tight as they can go...and then turned them back just a little bit. Even with the screws really tight (turned clockwise) it idles really high.


----------



## K-B

Turning them in leans out the mixture (more air, less fuel), which causes the engine to run faster. Try turning them both in until seated (do not force them tight, this can permanently damage both the needles and the carburetor body) and then back them both out 1 1/2 turns. Then turn in the L screw until the RPM's start to drop, the back it off a little bit. If it's still idling too fast, back the idle speed screw out until the head stops spinning. If it bogs when you hit the throttle, back the L screw out a little more (FYI, a little bit goes a long way - even 1/8" turn or less can make a big difference).
For the H screw, if you're not used to tuning a two-cycle engine and don't have a tachometer it can be difficult. To tune it by ear, you turn the screw in (clockwise) until the engine runs smoothly at full throttle, then back it out until there's a slight burble, or four-stroking sound.


----------



## nate81

The screw with the yellow arrow doesn't seem to be adjusting anything at all. I turned it 'out' (counter clock wise) just a bit, and started the motor...and it just wobbled the rest of the way out!


----------



## K-B

That is not an adjustment screw, so tighten that one back up. It looks like that carb probably has a fixed Hi speed screw, so the red arrow would normally be your L screw and the green arrow is your idle speed screw. If the engine bogs when you hit the throttle, turn the L screw out. Once that is set good, adjust the idle speed screw in or out until the engine idles smoothly and the head is not turning.


----------



## nate81

Would it be normal for the idle speed screw to have to be turned out 5-6 or more times? as opposed to 1-2 turns?


----------



## TheAlSmith

Yes it is possible for the idle speed screw to be turned out that far. It is tapered and only holds the throttle open to the minimum set amount it is allowed to close. That is how your low idle speed is maintained. Set your low speed screw to the leanest it can be and still give you solid throttle response and THEN adjust the idle screw (green arrow) until the head stops spinning. If you have a tac it should idle at about 2800 RPM but if not I'm sure you can tell by ear from experience how it should idle smoothly yet still not have the head spin. If you can't get the head to stop spinning then you have an issue with your clutch (weak or broken springs).

Anyways, I hope this helps.

TheAlSmithonline


----------



## nate81

Ok, i found out why it was idling soooo fast....when i put the throttle cable back on, there is another adjustment ...i had it way too high, which pulled on the throttle lever = idle high. soooo after i fixed that...i played with the 2 screws and i got it to idle very, very nicely, the head will not spin any longer. I still hear a 'pinging' noise and notice a slight delay and hesitance going from idle to full throttle. I think this may be a gasoline issue. I am going to dump all of my gas, and get some fresh 97 octane (after putting about 2 gallons into my car i will then put 1 full fresh gallon of pure 97 octane in my mix jug for my weedeater)

Another quick question....whilst weed eating, do i hold the throttle wide open?? It just seems like wayyyy to much power for the little weeds and trimming i need to do. Can't I just realtime adjust my speed (up and down constantly) and get the same effect? 


To all whom have helped...you saved me soooo much money and I have learned a lifelong lesson that I can teach my Son one day, so thank you!


----------



## K-B

Yes you can vary the power, however something to keep in mind is that running at low RPM for an extended time can not only cause carbon buildup in the engine, but it can also be bad for the clutch.


----------



## nate81

What would the downsounds be to running full throttle for extended periods of time? Can you 'blow' a engine like this?


----------



## K-B

No, they're designed to run at full speed with load. Running it at WOT (wide open throttle) for a long time with no load can be bad, so if you're trimming very light grass I would recommend you alternate between WOT and half throttle.


----------



## nate81

Thanks for everything


----------



## chadler2091

nate81, what was the cause of your problem listed in this thread. I am having the same problem.

Thanks.


----------



## nate81

did you read all 3 pages? it was my carb, i replaced it with a $30 one from ebay and it runs like new now!


----------

