This article is pretty basic stuff for people who know sleds and love to work on them just as much as they love to ride them. This is mainly for the first John Deeres that had the metal gas tanks, and it is targeted towards the people that are new to working on sleds. From what I've seen, this is the most common problem with the early JDs.

Gas Tank

To do this, it is best to remove the gas tank. This is simple. Just remove the fuel lines connected at the fitting on top, and unbolt the 2 brackets that hold it down, and lift it out. Next, remove the fuel line fitting, gas cap, and gas gauge. Then you should dump the old gas.
With the old gas removed, rinse the tank out with clean, regular gasoline, this will remove any water and rust sitting in the tank. This usually does the job. You also want to clean any rust off the fittings, a wire brush works well for this. Rinse them off well with gas or a light weight oil (WD-40). You may now put the gas tank back into the sled, and bolt down the brackets.

Next, you want to replace the fuel lines. Remove the plastic console from over the engine by removing the screws around the outside and the bolts that are located under the dash. Then remove the old lines from the Carb, and you should have already done this with the gas tank end. Pull the old lines out, and note the length, so you know how long to cut the new fuel lines. Use any 1/4 inch fuel line, from basically any auto/tractor/sled parts store/catalog. Cut the new fuel line the same length as the old line, and put it in place on the sled.
NOTE: One fuel line will go from the left fitting on the gas tank to the center fitting on the bottom of the carb. This is the one that will also have the inline fuel filter (shown below). The other one will go from the right fitting on the tank to the other second fitting on the bottom of the carb.
You will also want to replace the fuel filter, check valve, and two short pieces of fuel line including the fuel pickup line (shown below), and impulse line (short piece of fuel line that goes from the bottom end of the engine to the fitting on the side of the carb. which is demonstrated in this picture.

Carb Rebuild

This part can be tricky, especially with all the small parts and springs that Walbro carbs use. It is, however, usually the problem when an early Deere is running poorly. To do this, you will need a Walbro Diaphragm & Gasket Kit for your model (WR, WD, WDA) which will cost just about $10. It can usually be found at your local sled dealer.

To start, dissassemble the carb by removing the four (4) screws from the bottom. The fuel pump section of the carb will come apart, so be careful, take it apart slowly.
NOTE: Try to remember how they will go back together, because they must be in the correct order. CLICK HERE for a diagram of the order of the assembly. Be sure to keep the old springs and other parts for when it goes back together, these are reusable.
Remove the old gaskets and diaphrams from the plates, these must be completely be peeled off.

If some gaskets are stubborn, I reccomend using WD-40 to help soften them up and remove them.
Also, do not forget about the metering gaskets at the top.

Now, the plates can be put back together, be sure everything is there and in the right order. Walbros are infamous for having many small parts. After the carb is back together, place it back on the sled with the included gaskets, and reconnect the fuel lines, and if all is done right, you should have a well running Deere. You may need to do some tuning, CLICK HERE for tuning instructions.