Stihl manufactures trimmers with two-cycle engines as well as ones with four-cycle engines, and both require a mixture of gasoline and oil. One reason why one of these trimmers may die at full throttle is that too much oil is in the gas, which causes poor combustion. Improper operation, including overuse of the choke, can also be responsible. Poor combustion produces carbon deposits that foul the spark plug and exhaust port, making the problem worse. When cold-starting a Stihl trimmer, you must move the control on the control grip to the "Start" position and turn the choke on by moving the lever to the "Choke" position.
The choke restricts air flow to the carburetor, producing a fuel-rich mixture in the combustion chamber. Once the trimmer starts, move the choke all the way in the opposite direction to open the carburetor and allow air to flow. If you don't do this, the engine will sputter and die when you open the throttle, because too much fuel is in the combustion chamber to ignite.
One of the consequences of operating a Stihl trimmer with the choke on or a fuel mixture that has too much oil is that the engine smokes, which fills the spark arrestor screen with carbon deposits that block air flow. You must clean this screen periodically to prevent the engine from stalling. It's just as important to regularly replace the intake air filter or clean it by spraying it with compressed air -- if it's the felt type -- or washing it with soapy water, if it's the foam type.
Always close the choke before removing the air filter to keep dirt out of the carburetor. The trimmer can sputter and stall if it isn't getting enough fuel, and that can happen simply because the fuel filter is dirty. Fuel filters are inexpensive, and it's more practical to replace a dirty one than it is to try to clean it.
On most models, it's in the gas tank or on the cap. While you're cleaning the filter, try running the trimmer with the cap loosened. If it doesn't stall, the cap vent hole may be plugged; and if so, you should replace the cap as well as the filter.
Stihl hedge trimmer over revving
The carburetor is factory-adjusted for sea level, and if you use the trimmer at high altitudes, it may not get enough air for proper combustion. Most Stihl trimmer carburetors have adjustment screws for high- and low-speed operation, as well as an idle adjustment. The manufacturer's recommended adjustment procedure is to screw both the high-speed screw -- "H" -- and low-speed screw -- "L" -- clockwise until they seat, then back each off a complete turn.
After that, adjust the "H" screw no more than one-quarter turn in either direction. Make the adjustments while the engine is warm. Chris Deziel has a bachelor's degree in physics and a master's degree in humanities. Besides having an abiding interest in popular science, Deziel has been active in the building and home design trades since As a landscape builder, he helped establish two gardening companies. By Chris Deziel Updated December 19, About the Author.Discussion in ' Mechanic and Repair ' started by strikerMay 14, Log in or Sign up.
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Messages: 4. I just purchased a Stihl FS90 trimmer from a guy locally. He said it is about years old. It ran fine for a couple days, but now when I hold the trigger down, it will rev up and then bog back down to near idle and it will repeat this cycle until you release the throttle and it will drop back to idle then. Stuff I have tried: The gas tank is full. I tried with and without the air filter and it does the same thing.
Spark plug looks ok Tried adjusting the H screw and it did nothing Any ideas? My next things to try tomorrow are the fuel pickup and spark arrestor. I've also read some stuff online that the carb can get clogged with very fine gunk and that can do it?
I appreciate the help! Messages: 2, Beyond what you have done and intend to do check fuel lines for possible air leak or extremely soft fuel line that may collapse under vacuum. If you notice a change in rpm's you may have an air leak there. So I pulled the cover off and there is no spark arresting screen so that is not the issue. For some reason, I decided to remove the gas cap and rev the throttle and the engine ran full throttle.
So I took it out to cut and I would have to take the cap off, rev the engine up then put the gas cap back on. It would cut for a while and then go back to revving up then bogging down and revving up, etc. If I took the cap off again it would work again. Any ideas? Bad tank venting? Anyone have an opinion on what I should try next?Log in or Sign up. Sign up now! Site Upgrade Planned for Next Week! The upgrade is planned for early next week, with additional features being rolled out in the weeks and months ahead.
As always, we welcome your feedback and look forward to hearing your thoughts. Messages: 17, Like the title says my Stihl hedge trimmers are over revving bad.
Any ideas what causes this? RussellBSep 28, Messages: 1, Over revving at idle or over revving at full throttle? At full throttle. Male, from Michigan. Messages: 23, Maybe the high speed screw has turned from all the vibration and it is now running too lean. Check that, or have it checked. Ridin' GreenSep 28, Messages: What Ridin' Green said. BlainethompsonSep 28, Yeah, which model? My HS45 is a real hand shaker. It's a HS82T.
I'll check the High speed screw. My thought is fuel related but the mix has not changed.Forums New posts Search forums. What's new New posts New media New media comments Latest activity.
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I installed a new carburetor, fuel line and filter - no difference. I removed the exhaust deflector to check the spark arrester but it was gone. I cleaned out the deflector and exhaust area really not that bad - no difference. It starts and runs great, except for its failure to rev up enough to do some work.
Any ideas? HuskStihl Chairin'em for the sound. Assuming you replaced the fuel and impulse lines and have the carb adjusted properly with no improvement, I'd bet u'r ignition coil is going bad. You'll also get more replies if you post this in the chainsaw forum. Good luck. Mar 27, How do I get to the chainsaw forum? First off what model is it? Stihl didn't make an They made an or What are your carb settings on the L and H side? Does your saw have points or electric ignition? It sounds like you've got it nailed!String trimmers can be troublesome garden tools.
Difficulty in starting is often due to an issue with the carburetor carburator. In this article, I offer a list of troubleshooting questions to help you find the problem. I strip and clean a carburetor and point out where problems can arise. If you found this guide was useful and it helped resolve the issue with your trimmer, please take the time to share a link to it on social media, Facebook, Pinterest etc.
Usually though, the problem is caused by parts which wear out or become compromised in some way in the carburetor. Before jumping to conclusions and starting to troubleshoot, follow a proper start sequence. All two-stroke engines on trimmers and also four-stroke engines on lawn mowers, generators, and other small equipment are fitted with a device called a carburetor often shortened to carb in North America or carby in Australia.
Engines in older cars and other gas-powered vehicles also had a carburetor before the introduction of fuel injection in the s. The function of the carburetor is to mix a mist of gasoline and air together to form an explosive mixture which is burned in the cylinder of the engine.
Two-stroke also known as two-cycle or 2t engines are used on most hand-held garden power tools.
They have several advantages over four-stroke engines like the one in your car or lawn mower. Firstly, there is no sump or reservoir on the underside, filled with oil for lubricating the engine. A sump would be impractical considering that such hand-held power tools may be used upside down and at all angles.
Small four-stroke engines are fairly "primitive" and don't have an oil pump, relying on a "splasher" or "flicker" on the connecting rod to throw oil from the sump onto the piston and other moving parts. So this system would be ineffective on a two-stroke engine if it was used upside down. To lubricate these type of engines, you need to pre-mix oil with gas.
The absence of a sump and its oil content reduces weight.
Stihl FS90 Revs up and down under full throttle
Also two-stroke engines don't have valves, a cam shaft, or the other bits and pieces which operate the valves. This further reduces weight. So the result is a lighter machine, a higher power-to-weight ratio than a four-stroke, no requirement for an oil change, and less working parts to wear out or fail.
The greatest disadvantage of these types of engines is that because oil is burned in the combustion chamber or cylinder along with the gas, they produce smoke and are smelly which causes pollution in cities where scooters and motorbikes are the main means of transport. Low smoke two-stroke oils are available, however, which somewhat cut down on emissions. I have a bargain basement trimmer I bought in a large home store.
Unfortunately, spare parts are unlikely to be widely available for repairing such a model although the store may be able to get them from their supplierwhich was probably mass produced in China.
Still, it was cheap and I've got years of use out of it with no engine problems except the protection guard for the line broke and I had to make a new one. That way, you can be certain of getting service information, spare parts, and after-sale support.
Gas petrol is flammable. Keep all sources of ignition away from where you are working on an engine. This includes naked flames, cigarettes, hot surfaces, and tools which generate sparks e.
Rags soaked in gas can ignite, so dispose of them safely.Forums New posts Search forums. What's new New posts New media New media comments Latest activity.HOW TO FIX A WEEDEATER THAT BOGS DOWN, WON'T REV UP, KILLS
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It was running great when I put it up. A couple of weeks later I started it up.
My STIHL Saw Keeps Stalling
I idled great and seemed fine. However, it will not rev up. Pull the throttle and it bogs and dies. I have tried all the basics, gas, fuel filter, fuel, plug, carb, air filter, hoses Plug is new and looks great and appears to be burning clean and properly. As long as the intake is covered it runs ok. Uncover it and it's back to the same problem. Last edited: Nov 18, HD ArboristSite Guru.
Anne Illinois. Not sure what you have done to carb but take carb apart clean well. If that don't work try adjusting metering valve a little.The Stihl FS 55 is a straight shaft trimmer and brush cutter designed to let you easily maneuver it around obstacles on your property.
The FS 55 is run by a 1 brake horsepower. The "R" version of the FS 55 comes with a loop handle halfway down the shaft and the controls on the shaft itself, just below the engine. If the Stihl FS 55R starts to give you problems, troubleshoot it before calling a repair person. Mix 1 gallon of unleaded gasoline with 2. Shake the mixture to thoroughly mix it up. Clean the area around the fuel cap at the end of the trimmer. Turn the cap counterclockwise to remove it, fill the tank until you can see the gasoline level approach the opening, then replace the cap.
Pull up on the rubber boot over the spark plug, located on the very top of the FS trimmer, to remove it. Rotate the spark plug counterclockwise to remove it from the trimmer. Hold down both triggers, one on each side of the handle, until they lock into place. Pull the starter cord three times to clear the chamber.
Stihl trimmer FS55
Move the choke lever, on the left side of the machine, down to the lowest settings. The icon for the setting you want will look like a horizontal symbol between two horizontal lines. Press the fuel pump bulb, located right next to the choke lever, five times. Clean off the spark plug, replace it and return the rubber boot. Pull the starter cord until the engine starts. Squeeze and release the throttle trigger to put the engine into idle mode.
Pull up on the rubber boot over the spark plug. Unscrew the spark plug and clean it off. Check the electrolode gap on the end of the spark plug, as this gap should be no larger than.
Push down slightly on the external electrolode to close the gap. Replace the spark plug and the rubber boot. Move the choke lever to its highest setting, which has an icon that looks like a vertical line between two horizontal lines.