How Do I Mix Fuel for My String Trimmer, Hedge Trimmer or Chainsaw?

These garden power tools generally have a two stroke engine (also known as a two cycle or 2T engine), and to make them lighter, they don't carry motor oil on board as in the case of a lawn mower or road vehicle. Instead oil is added and mixed with the petrol (gas) before use.
In general petrol/oil ratio for 2-stroke engines is 40:1 or 50:1 which is 2.5% or 2% oil. 50:1 is equivalent to 20ml in 1 litre or just over 2 1/2 US fluid ounces per US gallon. 40:1 is equivalent to 25ml in 1 litre or 3.2 US fluid ounces per US gallon. 
After adding oil, swirl the contents around to ensure it's thoroughly mixed.Consult the manual of the machine for details of the recommended ratio.

Lawn Mower Won't Start? - Top 10 Small Engine Troubleshooting Tips

1. Use fresh petrol (gasoline). Old petrol can cause difficult starting. Make sure there is enough fuel in the tank and check the vent in the tank cap isn'tclogged
2.  The spark lead should be firmly attached to the plug, and the plug tightly screwed into the engine block. Try replacing the plug with a new one if the engine won't start
3. Most modern mowers have a control handle which needs to be pushed forwards/upwards and held in place to keep the engine running. Make sure this control is mower is held fully against the mower handle while starting.
4. If a manual choke is fitted, turn it on. Don't turn on the choke if the engine has been running in the last 10 minutes
5. If the engine has a primer bulb, press it about 5 times. If the mower runs out of petrol during cutting, it will need to be primed again
6. Check the air filter isn't dirty. Wash and dry foam type air filters in warm,soapy water. A paper filter can be blown out with an air compressor, but will eventually need to be replaced
7. Check the cable connecting the "dead man's handle" (the control which keeps the engine running when held in place) to the engine is not damaged or snapped
8. The carburettor should be tightly screwed or bolted to the engine
9. Make sure there isn't any water collected at the bottom of the petrol tank. If there is, drain the tank and use a piece of stick or long screwdriver with a piece of rag tied on (with a twisty tie) to soak up water
10. If the starter cord is hard to pull, check the underside of the deck and remove any clumps of grass which may be jamming the blade. Disconnect the spark lead before attempting to move the blade to remove clippings!

    

    Paper air filter

    
    

    

    Foam air filter

How Can Hand or Garden Tools be De-Rusted?

Remove excess rust with steel (wire) wool soaked in lemon juice or vinegar which are mild acids. Rinse the tools and allow them to dry. You could soak the tools for a period to remove excess rust.
Another alternative which definitely works is phosphoric acid. This is often a constituent of rust removing chemicals and can also be bought in gallon containers from companies which supply cleaning chemicals. It is a powerful acid and can also be used for removing limescale from surfaces. Usually it is diluted with water before use. The objects being cleaned are submerged in the solution and should only be left in the acid for the bare minimum of time to dissolve the rust, otherwise the acid will start to dissolve the underlying metal! I have cleaned an old vice pillar drill vice belonging to my grandfather which developed a thick layer of rust after being exposed to dampness in a shed for over thirty years and the acid completely removed the rust.
Once you remove the rust, rub some oil into them and wipe off any excess. This will help to prevent future corrosion.
Sand can also be used as an abrasive for removing rust from tools.
If you wipe tools with light oil after use, it helps to prevent condensation and subsequent corrosion. Guns and tools were traditionally given (and probably still are) a coating of oil after manufacture and before packing to protect them from dampness and rust.