It is part of the throttle governor – the has a 90° bend inside the engine and runs against a ‘thimble’ which has pivoted bob weights on it.  As engine runs faster the linkage try to close the throttle.

No- not usually anything inside the stop the shaft being pushed in.

You can probably find Aspera or Tecumseh parts manuals on line which show everything.

You have to adjust the angle where the screw is to get required performance – I used to do these routinely many years ago.

re mixture screw. Depends on vintage. Old carbs where the float chamber was just that feeding the simple spray bar in a tube eg Suffolk Punch mowers it was just a drain but newer designs with plastic bits the vaporisers are quite a refined and complex shape inside the float chamber and it is a mixture setting, eg Balmoral mower. I can’t remember the details as it is quite a while since I played with either. I’ve referenced mower names as I don’t know the actual engine but probably not B&S.

When engine is stopped, the governor shaft rests on the top of the weight carrier and (if pulled by the throttle spring) the throttle can reach fully open.  Any lifting of the weight carrier due to the weights spinning round will tend to reduce throttle opening.

Engine operating speed is a balance between spring tension and the raising of the weight carrier.

Unfortunately I don’t recall which direction the governor shaft turns in, but it should be simple to work out.  The actual arc of operation will be no more than perhaps 30°, probably less.

Highly unlikely that is it totally gunked up – there really isn’t much to these.  If it was so bad as to be gunked up, I’d be wanting to split the engine casing anyway to give it all a clean out

The ‘push’ from the governor weights will try to close the throttle flap, opposite to the pull from the spring which tries to open the throttle.  A quick search found a Youtube video where someone showed the workings https://youtu.be/cZWy9rNscLU

3000 rpm is the full load speed for a 50 Hz genset. Off load the governor should maintain engine speed at no more than 3150 rpm (5% run out)

When initially starting, if the engine speed is below 3000, the governor will open the throttle fully, to bring the engine upto rated speed, but close it partially as rated speed approaches.

As Noel says, check that the throttle closes as the engine speeds up.

Once upto speed, depending on the electrical load applied to the alternator, the speed can vary between 3000 (Full load) and 3150 (No load)

Trying to shorten the run out, to control frequency more closely, can make the governing too sensitive, and unstable, so that the speed is constantly varying, even with a constant electrical load.

Hopefully, any “hunting” will gradually be damped out, by mechanical and electrical inertias

The electrical control set up should limit, and control, voltage.

Usually. lacking means of applying a full electrical load, normal practice is to set the maximum speed, unloaded, to 3150 rpm. As electrical load is applied, the speed should fall until, what ever load results in 3000 rpm, will be the maximum that the engine can deliver.

If the engine is overloaded, and the speed falls below 3,000 rpm, the frequency will be below 50 Hz, with the problems that can bring.

Overspeeding can bring electrical and mechanical problems, so is to be avoided.

HTH

Howard