hi im 13 and about 175cm and about 50kg l have a yz85 lw that l am flat foot on and l wanna start motocross racing in austrailia but l wanted to no if l should start on the yz 85 and then move up or get a yz125 or yz250f and then start l have been riding 2 strokes all my life sine l was 5so l dont no if l wanna get a 4 stroke because l love that hit of power that the 2 storkes have so what do you guys think l should do??

You r tall for the 85cc but l still think u would do better to get ur foot in the door with a few race meets on the 85cc before u move onto the bigger bike. Then u really would be better off in Australia to go for something like a crf250r & not a 2 stroke 125cc. As l have previously stated the 125cc is r slowly disappearing from the grids here in Oz & r not being produced by all the known manufacturers any longer.
Racing mx in Australia does differ from other places in that not that many people race older bikes & we still have many race meets where the 2 stroke 125cc is race against the 4 stroke 250cc's. We also do not have allowances for modified classes so advice from those not living in Australia may be good advice for that country but not for here.
Being a bit taller u would find that u have a slight advantage over many of the smaller riders & once u have got the idea of how things r when racing u can move directly onto a bigger bike, but even in C grade many of the riders have been riding for a number of years so starting off there may be intimidating.
Regardless of which bike u choose to race u will still have to do ur 5 hours of coaching & again u may find that easier on an 85cc. But if u then choose to move to the 250cc u have to do another 5 hours coaching to move to the larger bike. These r new rules that have only been in place for a couple of years & designed to make sure the kids have a basic grounding in how to handle a bike before they r put in a race situation.

The other point about staying on the 85cc for just a bit is ur weight. You weigh about half a kilo more than my son who is considered very light (especially as he is 3 years older than you) he races 3 sections this year. The 85ccc section on the crf150r, the 125cc section (when they run separate from the 250cc & the 250cc section. He is an A grade rider but has taken longer to be able to ride the 250cc to optimum due to his weight as it is a lot of bike for someone who is under 50 kilos.

If you were in the USA l would say go with the 125 for a year or so before you have to be on a 4-stroke.KTM and YAMAHA are still making 125s and KTM has a sweet 150sx 2-stroke.Most kids struggle going to a 4-stroke from an 85cc. l do not know the rules there in oz land that Auburn was pointing out.so you are going to have to go with the flow.

l agree with Auburn that u should run for a while in the 85 class, 13 is pretty young to jump into the lites class. As far as 125 versus 250F, my first thought is to say u will be at a disadvantage on the 125, but as a novice who cares. No disrespect but obviously u r not going to go out & sweep the field in ur first couple years. So l say get ur feet wet on the 85 since u already own it. When u feel comfortable racing move to a 125 & when u reach a point that u feel the 125 is keeping u off of the podium move to the 250F.

stay on the Yz125 for a little wile longer and once you feel to big for the bike and the yz85 feels to small gat a 125 two stroke.