A Twitter user has recently posted a video apparently showing members of the Syrian rebel group Tahrir al-Sham firing a Chinese W85 copy of the Soviet 12.7x108mm DShK heavy machine gun from a short mount that is somehow clamped to the back seat of a common motorcycle. The video only lasts a few seconds and shows the gunner very delicately shooting single shots from the heavy machine gun. You can easily see the motorcycle bouncing from the recoil of the large round as the heavy machine gun is fired. It is suspected that the entire process was meant for a staged video production or testing rather than any actual combat use in Syria, due to the actions of both the gunner and his accomplice.
A DShK of any variant would weight between 35 to 50 pounds depending on the type, mount, and what kind of ammunition is used. In this case, if the common moped can easily support the weight of the average 150 (plus or minus depending on geography) pound adult, then a mounted DShK wouldn’t be an issue for a temporary time period. But due to the air filled tires and a single kickstand, it doesn’t appear that this mount situation can be useful for anything other than well-aimed single shots.