my next build is going to be a fat tired bike with front and rear engine two wheel drive. I'm going with twin Staton 7 speed chain drives. I need to sell some motorcyles to drum up some extra money for this project. I want a "Rokon" like woods trail bike. That big Pugsley bike would be exellant for this application but its really too pricey for me. I have a dual throttle adapter already that ties the throttles together. Staton's have freewheels so one engine can be shut down if I wanted to in some situations. Dual redundancy. But mostly they would be run together. I can't wait to get started on it.
You really don't need to tie the throttles together. In fact, for safety purposes, ya might want to keep them separate, in case one of them jams. The only time you'd need to synchronize throttles is if you were driving two separate rear tires. With tandem drive, one engine could actually be idling or off, while the other engine drives the bike.
I ran separate throttles on my twin-engined beast w/front and rear staton drive. Front was friction drive, rear was chain drive. Gear ratios were different. When you throttled the front engine then switched to rear drive, it sounded like a gear shift from first to second gear.That was on my no-suspension bike. On my front-suspension girlie bike, I used Staton friction drive on front and rear. Also, with separate throttles, you'd be able to finesse the exact amount of power needed, especially at low speed and around pedestrians and vehicles. Engine speeds don't need to be synchronized, but I bet you'll be on both throttles as much as feasible. I know I was on both throttles 95% of the time.
I also used a 4-liter Happy Time fuel tank to feed into both engines' saddle tanks. My Mitsubishi tanks were a bear to fill. I had to literally run the bike up a tree to fill them to the max, and then they'd spill over. With the central tank, only the HT tank needed to be filled, then it would distribute into the saddle tanks. The front tank was at a higher position because I was using a girlie bike, so sometimes it'd run outa gas at high speed. I even tried using a 12-volt VW electric fuel pump to solve that high speed fuel starvation.