Hi we have a Homerlite Mighty Life 2 Stroke Petrol Strimmer, that seems to object to having oil in it, we are doing the mixture right [50-1 as manufactures specks], but if we put oil in with the petrol it will eventually start but won't keep running once it has but if you just put petrol in it does, is this a fault on the strimmer? and if so what do we do next? Also would it cause damage by not putting the oil in? or should we make the mixture weaker?

Do not run that trimmer without oil in the petrol, or it will seize up and have to be thrown away. Very nearly all trimmers are crankcase induction 2 strokes, and the only lubrication the engines get is from the oil in the fuel. (Honda sells 4 stroke trimmers that use different lubrication arrangements, but I've never heard of Homelite doing so, and in any case you said it is a 2 stroke.)

If you are sure it is the oil in the fuel that is making it refuse to start (this would be very unusual, by the way) it sounds as if the carburetor is set a bit lean. The oil increases the viscosity of the fuel a bit and also tends to coat the inside of the jet, which may cause the air/fuel ratio to be a little leaner when the oil is present. You need to go through the carburetor manufacturer's procedure for adjusting the mixture. If you tell us what brand and model of carburetor you have, we can direct you to the carburetor manual. I suggest you do not attempt to adjust the mixture without having this information, because you are likely to make things worse.

Hi, thanks a lot for your advice,I think that we seem to have got it sorted now cos it at least starts [with oil in petrol] and will run so we can use the strimmer

It sounds like it is time to tune the carburetor. This generic description of how to do it may be useful:
http://store.chainsawr.com/blogs/tu...ment-and-tuning-of-a-chainsaw-carburetor

Note that trimmers like yours use chainsaw carburetors. Where it says you should start with the mixture screws 1 turn from all the way in, this depends on the brand of carburetor - in my experience one and a quarter turns is more common as the starting point. Before you start, however, measure the screw positions as they are now, so you can easily go back to your starting point where you at least know it will run. To do that, check where the screw slots are pointing, and gently rotate each screw clockwise until you feel it touch the seat lightly, keeping track of how far you have rotated it. Write down how far it was for each mixture screw. Then set them for your starting point and see if small adjustments make it better or worse. Hint: it is almost certain to end up within a quarter turn of one and a quarter turns out - but a quarter turn is a lot in terms of the effect it will have on how the saw runs. If you end up with it more than one and a half turns out, or less than one turn, the chances are you are doing it incorrectly, or the carburetor needs cleaning and perhaps new diaphragms or other parts. The diaphragms, in particular, tend to age, especially if it has been run on fuel containing ethanol.