Jon Weaver wrote:

I have a McCulloch strimmer which takes a 40:1 petrol/oil mix.
However, my mixing bottle (which takes 1 litre of petrol and has a
pointed top graduated in different radios) has become 'bloated'

This means that when you fill it to the 1L mark, there is actually
more than 1L in the bottle.

If I then top it up to the 40:1 with oil, I am getting a slightly lean
mix.

So, to counteract this, I have been adding a few extra drops of oil,
but the problem is that I don't know what ratio I am creating this
way.

I imagined that a slightly richer mix would be better than a lean one,
so I have made sure that I mix is on the 'rich' side if anything. I
figured that if it was too lean, then I stand the risk of seizing the
engine and doing real damage. But it is too rich, I would just have
too much oil, resulting in more smoke from the exhaust.

However, I asked my local lawnmower maintainer about this and was told
that it should be spot on 40:1.. To much or too little oil is just as
bad for the engine.

Is this really true? Is it a real problem running a 2-Stroke engine
with too much oil?

Even if too much oil is not ideal, is it so bad that you should throw
away a mix, if you added too much oil by accident?

Can anyone shed any light on this?

Very critical in that it must have oil in the gas, otherwise it'll seize
up. The oil is hoiw the engine get lubricated. If you can't have it
really close to the proper ratio, be a little heavy on the oil. You'll
foul a plug occasionally but at least you won't fry the engine. Being
lean on the oil is asking for trouble. Sounds like you have it pretty
well set though by adding a tad bit extra oil. You did the right thing.

--
John S. DeBoo