John Deere 520 Hard Starting

I"m desperately in need of assistance! I have a JD 520 that I purchased last fall, and have been unable to start it on any consistent basis. My theory is that too much fuel is getting to the carburetor, and the lines stay full even at shutoff, as there is a strong raw gas smell and slight leakage around the carburetor as the engine tries to catch. Here is what we know:
***When the tractor does catch (very rarely now) it runs smoothly and at full power
-Battery is fully charged
-Ignition and starter are fine
-Points are clean and are firing
-Gas is getting into the carburetor
-Old gas was siphoned off and tank refilled -All fluids check
-Ambient temperature of no influence (hot or cold)
-Even with the throttle all the way back, and the choke off, there is a strong gas smell and some discharge, though virtually nothing in the way of black smoke from the exhaust . . .just air and a puff of white every so often. Any thoughts would be most appreciated!!! Thanks!

QUESTION..... On those rare occasions that it does start, does it happen to start just as you decided to STOP cranking? If yes, right there's a good clue the bypass is not working.

You may also by now also have fouled plugs.

As a test of the bypass circuit... First, I would roll the engine over until the points are open. I would then replace the spark plugs with new ones just to ensure they are NOT the problem. I would next place a jumper wire (a clip lead) from the battery's negative terminal (assuming you're still original positive ground) to the battery post on the coil. NOT the distributor side but the BATTERY post of the coil. Turn on the ignition switch and attempt to start the tractor.

As soon as it starts, you must remove the jumper. Leaving it in place while it's running will usually cause misfires from arc over inside the distributor cap as well as overheating of the coil & burning of the points.

If you give up becasue it has not started, you must remove the jumper. If you leave it in place but not running it is likely to drain your battery and maybe cook the coil & burn up the points.

If it starts right up with the jumper but rarely if ever starts without the jumper it pretty nearly assures your hard starts are caused by a failure in the ignition system's bypass start circuit.

There are many possible casues for this failure. One common one is the coil being replaced with a 6 volter (that's good) and a ballast resistor that has unfortunately been wired improperly (that's bad). The above will tell you if a failing bypass circuit is the cause of the hard starts.

Run the test & post back your findings.