do u have to use 20% what would happen if i used 30% on the break in

I would reccomend using 20%, thats just my personal preferance though. If you do use 30% then your engine will be making slightly more power, but the engine wont last as long as one used on 20%. I'm not 100% sure about this though. I hope that this helped.

xXMAGIKXx

If you want to use 30% then thats fine. But I recommend breaking it in with 20% then move up after the break in is done. But thats just me, some say to break in the engine with the fuel and the percentage that you will use. But as I said before I would break it in on 20% them move to 30%.

how much more longer will it last

theres too many variables to give a definate answer, but when you run 30%, it raises compression, which shortens the life of an engine as compared to the compression created when running 20%.