Hi Stu,
It can be so frustrating taking action shots and no matter what you seem to do they come out all blurry. Now I'm guessing that you are trying to freeze the action as they come over the top of a jump etc., but what shutter speed are you using to try and do this, as you don't say? Also, what focal length, within the range of your telephoto zoom lens, are you using?
If I was taking fast moving action, keeping the camera in a firmly fixed position I would set the ISO to either 400 in bright sunny conditions or between 800 and 1600 when conditions are overcast and quite dim, with my shutter speed set between 1/500th and 1/1000th of a second. However, if you're trying to show movement then you'll have to learn how to pan the camera. The key here is to use a much slower shutter speed and follow the direction of your subject, making sure you keep them in frame, whilst you take the shot. But you must keep panning the camera as you depress the shutter button, otherwise everything in shot will be blurred. Again, if your subject is only moving at say 20-25mph using a 1/30th shutter speed will nicely blur the background and the spokes on the wheels. Of course if they are moving a little faster you will need to use a slightly faster shutter speed. One word of warning on panning though, it only works if you subject is moving in a straight line. It's no good if they are both moving forward whilst travelling in an arc through the air, because you would then have to move your camera both up and down as well as across and this creates a very funny blurring no matter what you do. So before you go on your day out get some practice on panning the camera. If you have a friend with a motorbike, get them to ride up and down while you take a few shots of them as they go.
Anyway, hopefully that has given you a few pointers, but the best advise I will give you is on your day out with this professional photographer ask them what settings and techniques they use to get their shots and copy them.
Best of luck,