I have been having a problem starting my 2 stroke quad bike.?

I have been using my quad bike fine for a long time. Today i went to my quad bike to start it and it sort of refused to start, then after 10 seconds of turning the starter motor it came to life and smelt really strange and i ran it for a good 40 seconds and revved it up. While revving it up using the throttle switch the throttle switch went a little loose and then the engine cut out and now it will not start at all??

Sounds like the throttle cable has snapped.
Ja.

You could have multiple problems here. The hard starting leads me to believe you have low compression in your cylinders and that's why it doesn't want to start. You could also have leaking crank seals. This is another problem with the 2 strokes. This is just some of the more common reasons why it isn't starting but obviously with out being able to run diagnostics on the machine, I can't tell you for sure.

Check all throttle linkages, as it smelt funny, and the oil is included in the fuel of 2 strokes, it could be over-fueling.
If this was the case, you may be able to smell fuel at the exhaust - don't stick your head up there while cranking though - you may get a backfire also !
If it is this, you need to adjust the links/clamps or throttle settings.

Looks like two problems here one, is your throttle cable has either come off or snapped and that you have poor compression, these engines need oil wether pre mixed or seperate tank, as they are nearly always at full revs, if you have just been putting in petrol and going round like a looney you will have burnt the piston rings and so now you have no compression to keep the engine running, new rings and possibly new piston head if you are lucky if you are not then it is a new head or a re-bore of the old one.