Question about Craftsman 25cc Gas Line Trimmer

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Having problems keeping my 25cc running any ideas as to what i need to do. It will start with full choke but if I go to run it just boggs out and dies

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This sounds like a fuel delivery problem....but could be something else. Make sure the in-tank fuel filter is clear. There is a small screen in the carb that also filters fuel, You may need to remove the carb and rebuild it with a kit. It is fairly easy to do and a learning experience for many. Make sure that let the machine warm up good (running on choke) before you move it to run. There are 2 types of carb rebuild is partial and cures a lot of ills and one has almost everything in the carb in it. They sell them at small engine repair shops and on Ebay too.

Posted on Aug 08, 2010

  • Len Nicpon May 29, 2011

    If your gas trimmer starts but will run only at low RPM, the problem is most likely a restriction in the exhaust system, due to carbon buildup in the spark arrestor screen, muffler, or exhaust port. The problem is caused by running the engine with the choke in the START position past the warm up period, running the engine at low rpm for extended periods, or improper gas to oil mix ratios (usually a combination of all three). The problem progresses over time, with a gradual loss in engine rpm and power, until it will only idle, or fails to start.
    On some machines repair may be as simple as cleaning the spark arrestor screen (which may be a simple 10 minute removal cleaning, and reassembly job), or it could be a clogged muffler or exhaust port, the inspection and repair of which requires significant disassembly and cleaning. If you do not have the proper tools and skills, I recommend you have the repair performed by a small engine repair shop.
    If you're handy, brave, or frugal (like me) you can attempt the repair yourself. You will need a set of metric allen (hex), and torx (star) wrenches, medium flat, and phillips screw drivers, and a strong solvent spray cleaner (carburetor, or brake cleaner), and of course safety goggles, particle mask, and solvent resistant gloves. An exploded diagram of your specific model is invaluable for proper disassembly and reassembly (unless you enjoy re-doing your repair, and guessing where the extra parts go).
    Depending on the model of your machine, various parts of the protective housing will need to be removed to gain access to the muffler. Remove the muffler, by removing the two allen or torx screws which secure it to the engine (on some models the muffler is secured by a spring clamp). Disassemble and clean the muffler paying close attention to the spark arrestor screen. Soaking the muffler overnight may be required to dissolve heavy carbon deposits.
    With the muffler removed, inspect the engine exhaust port for carbon deposits. crank the engine, the piston should be visible as it travels through its compression/combustion stroke cycle, and will travel below (open) the exhaust port on the exhaust stroke cycle. The entire exhaust port should be open, and clear of carbon deposits. If cleaning is required, crank the engine until the piston closes the exhaust port, and liberally spray the exhaust port area with the solvent cleaner (you may need to repeat this step several times). On a severely clogged exhaust port mechanical cleaning may be require (scrapping the carbon deposits from the port walls). I have found a very small flat screw driver works best. BE VERY CAREFUL NOT TO DAMAGE THE PISTON OR RINGS DURING THIS PROCESS! Once the carbon deposits are removed spray the port with solvent cleaner, then blow out with compressed air to remove any remaining debris. Reinstall the cleaned muffler, and reassemble the protective housing. Follow the manufacturers starting procedure, and your gas trimmer should run like new.

  • Roy Cagle
    Roy Cagle May 29, 2011

    Often times, on a 2 stroke machine, just readjusting the L mixture screw by turning it out counterclockwise 1/8 to 1/4 of a turn leans it out enough to where it will accelerate, throttle up and reach maximum RPM. The L (or idle circuit) in the carb is functioning at idle and increasingly adds fuel to the carb (aongwith the H circuit) as the throttle opens. At WOT, both the L and the H circuit are contributing all the fuel they can so the machine can attain and hold max RPM's. I have found that most folks use too "lean" a fuel mix, not the richer one that clogs the spark arrestor and exhaust port.; but both ways lead to problems. Carburetor tuning is imperative to get these machines to run correctly.



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