- Mon Mar 12, 2018 12:21 pm
#74797
That sound from the carburettor may be due to this:<
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A throttle opening that is too large for the engine speed or opening the throttle too quickly may cause ‘flat spots’ in carburetion and ‘pinking’ in the engine.<
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A sudden opening of the throttle or using a throttle opening that is too large may cause a temporary weak mixture. This is not due to incorrect jet sizes but to the greater inertia of fuel compared with air. <
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The greater inertia of fuel to air means that air will respond more quickly to the sudden drop in pressure in the venturi when the throttle is opened suddenly. Air rushes into the carburettor more quickly than fuel [the sound you hear?], upsetting the mixture strength and resulting in a temporary weak fuel/air mixture. The weak mixture causes the engine to hesitate – the opposite of what is normal when the throttle is opened.<
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Some carburettors correct this temporary weak mixture by fitting an ‘accelerator jet’, which squirts neat fuel into the venturi to compensate for the weak mixture.<
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The effects of this temporary weak mixture will be more marked with methanol than petrol, due to methanol having a higher specific gravity than petrol (791 for methanol, 737 for petrol).
