Honda is popular Japanese dirt bike brand. Honda is a huge company, they aren't just known for their bikes, they make cars, generators, lawnmowers, and more. Honda has a few different series' of bikes. Some of them are the 4-stroke CRF, the 2-stroke CR and the know out of production 4-stroke enduro XR.
Another popular Japanese mega company is Yamaha. Yamaha is also known for their sound and music related products. Many people, like myself, get a Yamaha because some consider the best product out there. Yamaha's series' are the 4-stroke YZF, 2-stoke YZ and the 4-stroke TTR. 
Suzuki is another popular Japanese company. Suzuki is becoming more and more well known for their cars rather than their bikes. Suzuki hit it big this summer with the signing of motocross superstar Ricky Carmichael. Suzuki has the 2-stroke RM, the 4-stroke RMZ and the 4-stroke DRZ.
Kawasaki is the smallest of the Japanese companies. They don't really make anything but  motorcycles and quads. Kawasaki is known for their great youth riding program that has started some of the best riders ever.
KTM is an Austrian company that is famous for their dirt bikes. KTM uses after market parts on their stock bikes. KTM's are the usually the most expensive and top-notch stock bikes. KTM isn't known for their motocross program but with the recent signing of Nathan Ramsey and young phenom Mike Alessi. Popular series' of KTM's are the EXC, MXC, and the SX. 

                                       

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