Carburetor Question


Old 05-14-02, 08:19 AM
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Tecumseh Dia Carb

I'm working on an old Sears Craftsman lawn edger. It has a Craftsman Model 143 631042 (Tecumseh engine). This engine uses a diaphram type carb Sears P/N 630989. I have installed a new diaphram and thoroghly cleand the carb but can't seem to get it adjusted properly. it has a dead spot when going to full throttle. If I advance it very very slowly it will rev. I don't believe there is any type of accelerator pump involved in this carb. It does have two adj screws. both are in good condition. I beleive the one closest to the filter is the high speed and the one closest to the engine being idle, but I'm not sure. Does anyone have any experience with this type of carb. I'm looking for ANY advice.
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Old 05-14-02, 10:48 AM
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The one closest to the engine is the low speed mixture
screw, turn it ccw a little and see if that helps your
acceleration problem.
Old 05-14-02, 08:16 PM
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Hello and Welcome Pasta to our Do-It-Yourself Web Site and our Small Engine forum.

The screw with the {"L"} marking is the Low Speed screw.
The screw with the {"H"} marking is the High Speed screw.

The problem your having is generically referred to as an off idle acceleration hesitation or stalling problem or condition. The low speed adjustment screw is adjusted inwards to much, resulting in a lean low speed fuel flow. The engine will seem to run well at low speed but not accelerate to high speed quickly.

To correct this, increase the Low speed fuel volume by turning the "L" screw outwards slightly. Retest the engine. Repeat the fuel adjustment and testing proceedure until the problem is corrected.

If the carb was rebuilt correctly and the fuel ports are cleared of any restrictions, the increase in low speed fuel will correct the problem.

The misunderstanding is that the low speed fuel adjustment only controls low speed. Not so. The low speed fuel circuit also supplies part of the fuel required to run the engine at high speed.

When both low and high speed fuel settings are adjusted and set correctly, both fuel circuits work together to prevent stalling during acceleration between low speed and high speed.

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