Weed eater stalls when given throttle

nate81 · 05-18-2010, 10:47 AM

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** · 05-18-2010, 02:22 PM

Hi and welcome to the forum

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 · 05-18-2010, 02:50 PM

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 · 05-18-2010, 05:07 PM

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

**Basementgeek** · 05-18-2010, 05:41 PM

Great

Now?

BG

nate81 · 05-18-2010, 06:53 PM

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** · 05-18-2010, 07:05 PM

Thanks..

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

BG

nate81 · 05-27-2010, 06:15 AM

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** · 05-27-2010, 07:11 AM

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 · 05-27-2010, 09:33 AM

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** · 05-27-2010, 02:34 PM

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 · 05-27-2010, 06:16 PM

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** · 05-27-2010, 06:39 PM

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** · 05-28-2010, 03:09 AM

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....

He is my favorite character in "Braveheart".

nate81 · 05-28-2010, 03:56 AM

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** · 05-29-2010, 08:23 PM

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 · 05-30-2010, 01:52 AM

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

sspenser · 07-31-2010, 08:47 AM

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** · 07-31-2010, 02:16 PM

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 · 08-01-2010, 04:45 AM

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!!