MTD Yard Machine 7-speed riding tractor/mower will not start after nopt being used for over 6 months. Re-charged battery and turns over great; filled with gas and pulled hose to make sure flow is at intake to carb. I suspect the ''kill switch'' that controls gas to the engine is not opening since I can squirt gas directly into the carb and it will start and run for as long as I keep squirting fuel. I have tried checking the seat switch... Troubleshooting indicates there is always 12 volts at the pints to the shut-off connector. Any advice?