2 Cycle Carb Question


Old 10-05-02, 07:21 AM
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Trimmer carb rebuild

I inherited a FS 80 Sthil trimmer and has a new carb rebuild kit on it but I'm having trouble getting it to run. It will start but strugles to run at full throttle. Someone have an idea of what to check or have the specs on settings for the carb. Any info would be helpful, thanks.
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Old 10-05-02, 09:20 AM
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Hello sbrickles. Welcome to our Small Engine forum.

If the new carb kit parts are installed correctly & the carb is reinstalled on the engine correctly, try altering the fuel adjustment screws.

Keeping in mind that both the high and low speed adjustments supply fuel to the engine at the same time and work together to allow the engine to run correctly.

When the LOW speed adjustment is too LEAN, the engine will idle but it will also bog down, stumble, stall and or fail to run well at high speeds or when attempting to accelerate.

To correct the condition, once the engine is warmed up & running on idle, increase the LOW {L} speed fuel setting until the engine just begins to run fuel rich.

Evidence of an overly rich fuel mixture is blackened smoke from the muffler. If this happens, turn the LOW {L} fuel screw in slightly.

When the engine will accelerate from idle to high speed without bogging down, stumbling or stalling, adjust the HIGH {H} speed fuel screw until the engine runs slighly fuel rich.

Watch the muffler exhausts for hints of blacker smoke or an increase in smoke. At this point slightly turn in that screw to just prior to an overly rich fuel mixture.

One must keep in mind that 2 cycle small engines DO NOT have governors. The engines top speed is controlled entirely by the fuel mixture. Too LEAN and the engine will overspeed and destroy itself in short order.

Running slightly fuel enrichened will control the top speed, ensure proper cooling, since the incoming fuel oil mix also helps to cool the internal cylinder temps and provide proper air cooling and cutting speeds, etc. Fuel settings are critical and necessary adjustments that must be properly and accurately set.

Read the manufacturers online web site for product information, problem possibilities, causes and solving methods, part locations, disassembly, reassembly methods, repair proceedures and instructions, pictorials and schematics, which may be available online.

Read the recent postings and replies offered within this forum, for other postings and replies on this topic of two stroke engines.

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