Do you train at a club? Has your instructor given you any tips on how to stop this?
Personally I'd stop the activity (jumping/weaving etc) as soon as he jumps to nip and go back to the start of the obstacle, get him to do it again, again if he jumps to nip I'd stop and only click and treat (presuming you use clicker - great tool!) when he has done it without biting.
At our club we also use a target disc to try to get the dogs focusing on going forwards rather than focussing on you so that might help. Again, it helps if you use clicker but you get them to go to the target to get a treat and click when they touch the target, you can then use the target after an obstacle and get the over a jump to the target, then 2 jumps etc etc. It also helps to speed them up through the weaves as they're focusing on getting to the target.
Another route you could take would be to get him playing with a tuggy toy, he does some jumps etc (no biting) and then gets to take his biting behaviour out on the toy.
I hope one of these helps, if not I'm sure the real experts will be along shortly!
