The dip stick broke off in your sons Yamaha ttr90 and there is a couple pieces that you cant get out - help?

I know nothing about the Yamaha TTR90 - but there exists a 'magnetic pickup tool' that might work for you if the pieces of dipstick will stick to a magnet . It is available from bike dealers and online. It is the size and shape of a slim pen that extends out to 12-18 inches. On one end is a small magnetized button. This is very useful for getting anything metallic from places too narrow to get your hand in, or off the garage floor if you are too lazy to bend down. In the UK it would cost a couple of pounds, so quite cheap. It will definitely go down the oil filler holes of any motorcycle.