After purchasing this 84' 200x for 300.00 and just letting it sit for a few months too long I found my brother in my barn dismantelling his mint 81' ATC200 with intentions of using the engine on my project trike. Well knowing that there was no turning back now I proceeded to help him take his trike apart. He sold his old trike body parts on ebay and that paid for the new 200x ones. The original 200x engine had been taken apart by the previous owner and never reassembled so it wasnt like my project was going anywhere. We had the entire trike stripped of everything but the rear swingarm in about an hour. The swingarm pivot pin(bolt) wont come out so we opted to leave it in. That made it really difficult to paint the swingarm and frame that were spraypainted the wrong red and ugly white scheme. We sanded the frame and repainted it the correct colors.
The paint dried and a week later we got enough motivation to try and mount the engine. We used the stock 200x motor mounts with hardly a problem. By using the carb intake manifold from the 200x the x carb worked no problem. The airbox will mount the same way as the stock would fit. We used the entire electronics harness from the donor trike and made some minor modifications to get the new light to connect. Just match up the wire colors and your halfway there. We purchased new moose handlebars and mounted them. The gas tank that came with the 200x was in pretty good shape so my brother is pretty skilled at restoring them so he made it look brand new again, luckily there was little rust in the tank.
The rear brake was modified to use the old chrome foot brake from the donor trike to activate the brake. The 200x motors have the foot brake mounted to the engine but the old 200's dont. We welded a bar to the 200x foot pegs to act as a pivot and attached a linkage to the foot pedal and master cylinder.
New rear and front axle bearings made it roll straight again but that was after we found it was wobbling around the shop. In the process of doing that we found the hubs were from a 400ex and were sloppy on the 200x axle thus ruining the axle and hubs. Use the proper hubs please! New axle, new hubs, new tires and 8 x 8 stock rims from my trike since I got new 10 x 10's from ITP.
DG Power 4 exhaust and the 200x carb with a 118 main jet works well with the 200x head and new pipe. I use a 15 main jet in my stock 200x with a Krome Power 4 from DG.
To bottom it off we ordered new rear 18" maxis razr mx tires that still have to be mounted.
To top it off we ordered new plastics all around from Maier Plastics for about 300.00 total. You need the mounts from the old ones! New decals from ATC Heaven made it pretty.
Mistake 1: Sprocket ratio, get it right or your ride won't be. The stock sprocket ratio on the 81' 200 is 11/47. Don't go bigger in the front unless you have to and if you do just go 1 tooth. The rear should not change more than two or three either from stock. Any more and your performance could suffer greatly. I made the mistake of using the stock 200x rear sprocket with a 40 tooth front just to get it to fit at first. This has proved to be a waste of money. If you use a normal 200 atc as the donor engine you need to use a larger rear like the stock size. Something like a 45 tooth would work best on the 200x seeing as it has smaller tires.
Mistake 2: Put the 200x head on the donor 200 bottom, I didn't at first and took the entire trike apart to bench the engine so that I could. While your at it and have the head off go one step further and remove the piston jug with the piston still inside and use that also on the 200 donor bottom. It's very easy and takes only a couple minutes. There are a couple pics here of me doing it. The 200x piston is higher compression and not using it if you have the parts would just be stupid and a loss of power you will regret not having.
MORE UPGRADES YOU CAN DO:
Use a 185s not 185 bottom end with 200x jug and head, a xr 200 cam and springs, and an xr200 carb even though you need to heat up the 200x airbox boot to fit it. Bikerchick on Ebay sells a high performance cam with .39 valve lift that requires new springs, and maybe a little grinding on the head (I might be wrong). The cam is only like 55-60 dollars and would be well worth it if you have your engine benched anyway.
DONT FORGET A FULL GASKET SET!
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LIVE IN EAST PA. OR NEW JERSEY THEN CHECK THIS OUT 
