Hello All,
Both the Maico 685 and ATK 700 have the same motor. It is a 685cc two stroke Zabel motor originaly made for sidecarcross racing. The 620cc is also a Zabel motor. I have a 685 in my one of my sidecars. It is a beast.
I have ridden a 620 also, it is a more docile version. The motors were based on the old Maico 500. Zabel originally built big topends for the Maico, but with the demise of Maico he built his own motors. Starting with the 620 the built the larger 685. Zabel now builds a true 700cc. I also have one of these. This motor is current sidecarcross World champion.
www.zabel-motor.com The 700 has more power than I need. It is almost unridable on our small Ca. mx tracks, but I love it for GPs. I have a KX5 sidecar and it is nothing in comparison. Not many ATK 700(685)s were sold, only a handfull. Zabel motors are readily available in Europe, and you have to get parts from Germany. I picked up parts to keep mine running on a recent trip to Europe where I met up with the KX500Freak. If you have any more question, I should be able to answer. Keep on roostin',
Mike the Tall
KXsidecar