Hi, been on hols so a bit late in on this thread.
About time the MTA4 population increased a bit!
In case I'm not too late and it's already been done, whoever was doing twin tank mods, I'd recommend running the tanks in series (rather than parallel with a t-junction). Simpler pipework, less chance of air leaks developing as less junctions. Also if in parallel and one of the two tanks runs out before the other it just starts introducing bubbles into the fuel line and buggering your tune. Rig them in series is the way forward.
It is generally accepted that the thunder tiger manuals are terrible and say all kinds of crap. The favourite is the fact that the MSN is marked as the LSN in one or two of the pictures. If anyone having trouble tuning and hasn't been told or figured it out, hsn is big copper screw, MSN is the large silver screw that's easily accessible on the side of the carb (don't touch it), and the LSN is the little back screw in the grommet on the opposite side of the carb to the MSN, where the throttle linkage attaches to the carb - right under the air filter so hard to get at. Lots of people start off merrily tuning away on the MSN thinking its the LSN and not understanding why things arnt having the effect they should.