The FS85 starts and idles fine. And if i repeatedly press the primer bubble, it will rev up. One i get the rpm up using primer bubble, hit the throttle, i get about 2 seconds of full throttle, then dies out. I have read the many posts prior to this. Spark plug fine, screen in muffler fine, new gas/oil mix. Adjusted carb to factory setting. Any thoughts?
Pumping the primer bubble while the engine is running should cause the engine to over fuel and stall (if the tuning is correct). Sounds like its not fueling enough, pumping the primer is forcing fuel through the carb causing the engine to pick up rev's, but this is soon exhausted which is why it wont rev on the throttle.
* Check that the fuel line is not damaged and drawing in air. (if this is intact try the next step)
* Strip and clean the carb. Replace any diaphrams if needed.
* Check gaskets seal between carb, air filter and cylinder.
Just out of curiosity what standard carb settings did you use.?
Testimonial: "Per what i read, High speed turn all the way counterclockwise. Low speed turned all the way in, and back out 1 full turn. The bottom one didnt seem to make much of a difference. Tighten in or out in quarter increments to a full 2 turn out"
Hi brenda_st292
You still have debris/trash in your carb...or the jets are not adjusted right, follow the directions below
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Sounds like you have dirt/debris in your caburetor jets,fuel passages or a diaphgram that is becoming non-flexible.
Check/Clean/Replace your Air Filter, a dirty air filter can make your engine run to rich with fuel.
Note: ALWAYS USE COMPRESSED AIR TO CLEAN YOUR JETS AND PASSAGES, VERY IMPORTANT.
Note:Before you disassemble the carburetor:
Write down on a piece of paper or take a picture of how the linkage attaches to your carburetor for later reference when you go to reinstall your carburetor.
Mark each piece with a awl, or some kind of instrument that will make an alignment scratch before you disassemble the carburetor into separate pieces.
That way you will know which way it goes back together when you reassemble it.
Sometimes you can get by with priming the carburetor or by using a very small shot of starting fluid and letting it run a few times like that, and it will flush the gunk out of the jets,but most of the time you will need to rebuild the carburetor.
Be sure to check your fuel tank for water and dirt/debris, if there is water/debris then you need to clean your tank.
Check you fuel line condition after a while they will degrade and need replacment.
Check/Clean/Replace your fuel filter if you have one, normally they are located in the fuel tank of chainsaws and weedeaters.
When you remove your fuel lines from the carburetor be sure to make a drawing to how the lines are connected to the carburetor or take a pictue for later reference.
Normally the big line will be the line the fuel filter is connected to inside of the tank.The smaller of the two lines is the return to the fuel tank from the carburetor after it is pumped thru the carburetor by the primer bulb.
Make sure you are using fresh fuel...and oil if your using a two cycle chainsaw or weedeater with the oil to the right mixture...too much oil as it can cause hard starting and excessive smoking.
If the chainsaw/trimmer is over a couple of years old, then I recommend that you buy and install a new carburetor repair kit,because the diaphragm will get hard and that will cause it to be hard to crank.
The diaphgram may look good and flexible, but it can be deceiving and not act as a fuel pump as it should because it has become too hard and will cause hard starting,start and run and shut off, etc.
When you clean your carburetor, I recommend that you use a laquer thinner type cleaner to clean and dissolve the laquer build-up in the float and needle jet passages.
Be sure to remove all plastic and rubber parts before using the laquer thinner because it can dissolve the plastic parts and render them unuseable.
Be sure to use COMPRESSED AIR to blow out all the fuel and air passages.The higher air pressure is needed to blow some of the trash/debris from the fuel or air passages.
Be careful when blowing out the passages, because there are sometimes small rubber type seats in the bottom of some of the passages.
Keep in mind that the float (if you have one) for the carburetor must be level when you go to reassemble the carburetor or follow the instructions you get with the carburetor kit, or you could also ask the parts man that you get your kit from.
When you clean your carburetor and remove the jet screws, you will first need to lightly seat the jet screws.
But before you lightly seat the jet screws count the number of turns it takes to seat the jet screws from their original position.
Be sure to mark the turns down on a piece of paper.
That way when you put the jets back in, you know to lightly seat them first and then turn them back out to their original position before you started.
Note:
The little spring inside of the carburetor goes under the float arm.
That is where your fuel inlet needle/float valve is located...on the arm at the end.
Normally there is a small indetion in the carburetor base and a small protrusion on the underneath of the float arm where the spring will be in the right postion for installation.
The spring will set in the indention and you will install the float arm with the needle/float valve and float rod into position over top of the spring,you will push down until it is in position and then you can tighten the screw that holds the float arm assembly in position.
Once you have your carburetor cleaned/rebuilt that should solve your problem.
Please take time to rate me
Bud
Sounds like the main jet or the diaphrams in the carburetor are deteriorated. Remove carb and soak in a good carburetor dip style cleaner and rebuild with a new kit. Also replace the fuel line and filter and use a fresh gas mix.
SOURCE: hi, have a stihl fs 85, runs fine for 10 minutes, then just cuts out. tried cleaning carb, muffler.
Two things spring to mind, fuel tank breather, to rule this out slacken off the filler cap when the machine starts to die, if it picks up again change the tank breather, or the ignition coil is breaking down when hot, this would require a replacment unit.
SOURCE: stihl trimmer must use choke for full throttle
Sounds like a tuning issue and carb problem. Before you go spending money on carbs or carb kits and start stripping down the carb, try this first.
*Unscew both H and L tuning screws ( not all the way out but back them off)
*Pull over until the engine fires up, it should run for a second and cut out.
*Screw both the H & L all the way back in.
*Then reset the carb to standard settings.
*Unscrew the H tuning screw 3/4 of a full turn.
*Unscrew the L tuning screw 1 full turn.
This should be the standard settings.
Start saw as normal and see if its any better. Failing that your probably looking at cleaning the carb or replacing diaphrams.
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