You could probably find something a bit more unique by shopping online but it is much more important to have a helmet that fits you properly otherwise it is not doing the job. Just look up your local directory and find what shops are in your area and go visit all of them.
That way you can try the helmet on and be sure it fits. Ask for someone with experience in fitting helmets to serve you. You only have one head!

Folks – the reason the asker is looking to do this mod is because AMA now has a class for the 105cc modded 80's and 85's.

To be competitive in this class, and since no manufacturer is currently offering a 105cc model, this is the only option.

Standard cylinder on this enigne in nikasil. No sleeve.

To do a big bore kit you will either need to have a liner installed in the cylinder (not the most reliable option usually), or purchase a complete kit which includes a bored and re-nikasiled (or other plating) cylinder.

Because of the change in cylinder volume, standard porting will NOT work. The porting needs to be matched to the new engine displacement.

You can purchase a complete setup like this from shops like Lukes http://www.lukesracing.com/luksr/cr85bigbore105p04.htm

Another option which will actually give much better overall power is an increase and bore and stroke to the new 105cc AMA limit. It's more expensive, but will give at least 20% more torque and midrange power than just a bigger piston.

Companies like Max Power offer these kits http://www.maxpower-engines.com/big-bore-kits/cr105.htm

He'll have to also remember that putting this much more power thru the engine can result in decreased lifespan of transmission and clutch components. Just something to keep in mind!

My personal choice would be a cr 85 expert.

Honestly you will have to look around and ask individuals or sales people. i had in the past a 2 stroke honda cr125, i loved it, now i have a 4 stroke suzuki dr250. basically a street legal dirt bike, it doesnt seem to have as much power as my 125 did but it does have equal power throughout the rpm range where as my 125 only had great power in high rpms during the powerband, all and all if it is trail riding and a little motocross and you want something cheap and easy to work on i would go with a 2 stroke, top end rebuilds are very easy to do, and there are plenty of shops around the country that work on 2 and 4 stroke motors. good luck!!

Yeah, a new 125 starts at around 5 grand so with 500 bucks you could maybe get an old used Honda or Kawi 125 that's been thrashed and beat. You'll be inheriting a decade of problems and abuse that the previous owner will be glad to unload, so plan on steadily spending cash in the future.

Your only other option is to hit auctions and estate sales and hope for a bike that somebody has had sitting around in their garage, full of 2 stroke gas that's been varnishing the innards for years. Then you'll get to know the inside of that engine pretty well as you clean all that crap out.

And what's with the 50mph? Are you racing this thing? I don't know if I've ever gotten up to 50mph on a dirt bike, but I'd guess that any mechanically sound 125cc can eventually get to 60 on a long, flat surface. Honda 125s claim a 60mph top speed.

Ebay there is always someone parting out a bike. Or a cycle salvage yard. Most Go cart racers buy the carts with the engines or buy a new bike and sell the chassis and parts. They make carting engines Ive seen many on ebay and at carting shops.

At 13 a good used cheap dirt bike would be a 125 2 stroke (any make)

Not just a ton of power and with the 4-strokes taking over the dirt bike world you should be able to get one at a pretty decent price.

Check your local dirt bike shops for postings.
Good luck!

Well since most moto x tracks don't have a web site…i'd visit some of your local bike shops. clubs and enthusiasts advertise with flyers and such at these places. most bike shops have people working there that also enjoy riding so there is a good chance that the employees can steer you in the right direction. that's how i found some of the best places to ride back in my riding days.

Craigslist, if your looking for a used one. brand new, i always go to peb boys they will have them cheap if you need one right away. if your taking your time, i'm sure you can find a small shop in your city that will have what your looking for at a very cheap price, look in your phone book call some small shops and price them it's that easy.

Giant STP2's are popular, they retail for about $1000 but they can be found on special in some shops for around $900. When bike shops get the 2009 season bikes in they usually discount the prices on the 2008 seasons bikes. Some shops are currently selling 2009 bikes and if they aren't they will soon.