How to put new governor springs on?

The maximum rpm is regulated by the governor - most small machines powered by petrol engines where high rpm would be a problem have a governor that usually fall into one of two types. Machines at the budget end of the market tend to use a movable vane inside the air cowling and as the engine speed is increased so is the air pressure against the vane increased causing the vane to move against it's return spring and in doing so tends to pull the throttle towards the closed position slowing the engine until the spring pressure is in equilibrium with the throttle pull spring.

Leaves, grass and other stuff can find a way into the air cowling and jam the air vane operation and is commonly the cause of overspeed as is general wear, incorrect assembly or maladjustment.

Engines at the more premium end of the market tend to use a centrifugal governor where the gubbins is inside the engine crankcase though the operating principle is similar - the throttle butterfly is pulled open by a spring connected to the hand control and the governor arm will move as the speed increases tending to pull the throttle closed until again and equilibrium exists between the two springs. This type of governor is reliable but the connections to the throttle are just as prone to wear, damage or maladjustment.

It is many years since I laid hands on a Lawnboy mower so I am not really familiar with the model but the principle of the air vane governor is fairly standard.

Briefly, the air vane and carb throttle butterfly is connected together and biased by a spring into the basic position where the throttle butterfly is open and the air vane is close to the fan. When the engine is running the air vane is forced away from the fan closing the throttle until engine revs/air draught and spring tension is in equilibrium.

The throttle control is connected to the linkage via a spring and increasing the engine speed increases the spring tension/air vane bias towards the fan, thus opening the throttle butterfly until the increased air draught moves the vane and tends to close the butterfly until a new equilibrium is reached.

There are two main types of governor and the centrifugal type tends to be reserved for heavier stationary type engines. Most portable lightweight appliances use a vane-type governor where a vane is placed adjacent to the cooling fan so the faster the engine revs the more air is moved and the more the vane will move against it's restraining spring.

There is a spring biasing the throttle to fully open and this spring is connected to the throttle or speed control lever.
There is a link connecting the throttle to the vane. After starting the engine speed will rise until the governor vane moves under the rush of cooling air forcing the throttle butterfly to close against the spring pressure until the vane pressure and the spring pressure are equal and therefore a constant engine speed is achieved.

Moving the speed control lever to increase speed tensions the spring and opens the butterfly causing the engine speed to rise until the vane force again equals the spring pressure.

This is a fairly basic but very common type. There are variations using two or three springs but the principle remains the same.

Hi Myles:
Since I don't know your machine, I can only give you the logic that I would follow if I were given your box of parts.
- The springs are intended to return the trigger to the idle position.
- With the motor off, Move the trigger from idle to full on, then back to idle. That's what is upposed to happen with the spring pulling it back.
- The other spring is connected to a governor. that is sometimes a "vane" that gets air from the blades on the flywheel, but the idea is that when th engine is under load, more throttle gets applied.
Consider it a fun project in logic.
Play with it, and all of a sudden all of the bits will be right and you'll be cutting grass like a mad thing.
Cheerfuls.

Dose your motor have a manual choke or automatic?

Maybe this will help from the service manual.

I believe the white flipper under the flywheel cover you are referring to is the 'air vane governor'. Its got a blade on one end that curves with the flywheel. Its on a pivot with a spring on the other end to the carb linkage. As the flywheel speeds up the fan pushes the air vane away which in turn adds tension to the governor spring. Controling the speed of the motor and preventing over revving.

From the governor 'vane', on end with a small hole in it is for one end of the spring........the other end of the spring goes to the throttle arm on the carb. YOU MUST HAVE THE CORRECT SPRING WITH THE PROPER LENGTH AND TENSION!!!

there should be a little screw to help adjust your idle try that..counterclockwise to add more idle, clockwise to slow idle..

I am not sure what type or how old your mower is but most have whats called an "air vane governor". This system uses air flow and a spring to control a vane back and forth. One problem is debris sometimes collects in the system blocking air flow. When this happens the engine will over speed. The other is if the spring breaks or detaches from the governor.

You should avoid running the mower at all until you are sure you have found and fixed the problem. Over running can quickly cause catastrophic damage to the engine.
Inspect the governor and make sure it's moving freely and that there is no blockages in regards to the air flow. If you find that the governor is not moving freely you can attempt to control it manually when the engine is started but only after you have positively identified the governor as the problem.
If you are unsure where the governor is located please respond back with the make and model of your mower.
Hope this helps.