Stihl brushcutter [four stroke] wont rev.

clean -rebuild --replace carb

check that you have reconnected the fuel and primer lines properly

Here's a link to your owner's manual,look at page 26 for carburetor adjustments,I have 3 stihl's,a blower,weedeater and chain saw,had them a long time,never had to adjust the carb.What problems are you having?Clean your air filter or replace it if's real dirty and can't get clean,use 50;1 regular unleaded gas and oil mixture,put a new plug in it,same as you were using,Autozone has them cheaper than the Stihl dealer.Are you using your choke and throttle correctly when starting?On mine,I set the throttle,lock it in,put choke on close,pull a few times,no more than 5,then open choke and pull,it should start,is your spark plug getting oil-gas on it,if so then your flooding it at start up,use fresh gas mixture.I wouldn't adjust the carb. https://www.stihlusa.com/WebContent/CMSFileLibrary/instructionmanuals/FS160_180_Manual.pdf

Check valve clearance. The four stroke engines need regular checks on the valve clearance's

Check valve clearances

1. Try depressing the brake handle when starting.
2. The battery has not been charged.
3. The battery is hooked up wrong. This is often the reason for blown fuses.
4. There isn't enough gas or two-stroke oil in the scooter.
5. There is a gas flow problem, especially on the Euro Scooter or Yamaha models.
6. The spark plug wire is not connected.
7. A low battery or bad relay can cause the scooter to only start by using the kick starter.
8. There is no spark to the spark plug. The coil is bad and needs to be replaced.
9. Turn the key to the "on" position.

You need to check for a spark. There are a few ways to do this. The easiest way is to remove the spark plug and put it back in the spark plug cap. Then ground it to the engine - you should be able to lay it against a non-painted portion of the engine. Make sure there is good metal-to-metal contact. In a semi darkened area, attempt to start the scooter. You should see a definite spark at the tip of the spark plug. It's hard to see in direct light. If the color of the spark is blue, that means it's a strong spark. A white color is less strong, and a yellow color is weak. Most scooter starting systems are a bit weak (compared to cars). Even a yellow spark should start your scooter just fine.
The spark must occur at the right time. Just about all scooters made since around 1980 have an electronic ignition. These systems can rarely be set. In general, the spark occurs just before the piston reaches the top of it's stroke. There is a slight delay between the spark plug fire and the fuel-air mixture ignition. That's why the spark occurs a little early. Most ignition systems have an advance unit build in. As the engine speeds up, the time of the spark retards a little bit. This helps the engine fire the mixture at the proper time

There are a lot of tiny fuel and air passageways in the carburetor that must be kept clean it order for your scooter to run right. Carefully, take the carburetor apart. This can be relative easy (on a 50cc scooter). The carb has tiny passages that can get gummed up. Your scooter will not run correctly if the carburetor isn't completely clean, so take your time. I use a gallon container of carb dip (you can get a gallon at your local auto supply store).
First, remove all of the rubber and gaskets or they will get damaged. After a 20 minute soaking in carb dip, I blow out the carb with compressed air. You have to get all the jets and the passageways clean. Be sure the jets are clear, especially the starter jet. Sometimes carb cleaner won't clear out these tiny jets. Use a guitar or a piano string, a strand of copper electrical wire, or a tiny drill bit pin vise. Be sure not to increase the size of the hole in the starter jet or you'll change the tuning. Carefully reassemble everything, checking for cracks in the rubber carb boots and the gaskets. Replace them if they are old and cracked. Be sure and remove all rubber and gasket material first or they could get ruined. Spray carb cleaner also works if you're diligent.
If you have an electric choke, check it to make sure it works. Check the resistance between the wires - you should see around 10 ohms or less. Measure the length of the choke assembly. Remove the choke from the carb and plug the wires into a 12V source for 15 minutes. The choke body should be warm. Measure the length again - it should increase by around 1/8".
Next, consider whether your exhaust pipe is clogged. This is especially a problem with older two stroke scooters. The unburned fuel/oil mixture builds up in the exhaust pipe along with carbon over time. If the exhaust pipe is clogged, your scooter will run terribly or not at all. It can be difficult to tell if the exhaust pipe is clogged. The easiest way to tell is to remove it and try starting your scooter. It will be a bit loud - two strokes will sound like a chain saw. If it runs with the exhaust pipe off, you know that is the problem

hope this helps

John

adjust the carb. the fuel air mixture is messed up. try adjusting both screws to the right

The problems you are having sounds very much like a blocked exhaust port/silencer. On these small two stroke machines it is normally the cause of lack of power or not revving. Happy gardening !!
Stantheman 19/09/2010

ok buddy on carb will be a screw try fiddle with this mixture screw on carb below get back to me with results

Jets in chainsaw may have build-up. A good build-up remover is called SeaFoam. Add this by direction to the gas. When using the SeaFoam you need to run full throttle with intermittently full choke until motor runs smooth with no choke.

Double check 2-cycle mixture. Too lean mixture in the chainsaw wont stay running.