Assuming a Briggs & Stratton 'Classic' type engine (most common) ....
Thanks to emmission regs and cost-cutting exercises, the carburettors on Briggs engines haven't had any adjustments whatever for some time.
If there are 2 govenor springs under the air filter, then the engine has a governed idle, and you're stuck with it as it is. There's no point in messing with the idle spring tension - the carb has no idle circuit, and so below a certain RPM it will simply not run.
You CAN adjust the high speed RPM by bending the main spring anchor point - but you need a tachometer to do this (or an experianced ear!). Regardless, the differance between MIN and MAX will only be about 800 RPM.
phil_saunders(a)bigfoot.com
Phil Saunders, April 2010
