I bought a used Tao Tao ATA250D off a guy awhile back and it did not have any spark. I installed all new electrical components and now have spark. I installed a new carberator, shut off valve and fuel filter but the ATV still will not start. I verified the "T" on the flywheel was at top dead center while the piston was all the way up. Any help will be appreciated very much!! Like I said, it has spark and gas.

 

Has to have fuel air and spark at the correct time. Did you change and gap the plug? Have you set valve clearance? .004 both exh and int. Take the aircleaner off, spray starting fluid in air horn, attemp start.. Did it try to start, even a pop? Fuel issues. No pop. Electric. Did you check the plug wire? Is everything grounded? Is the spark kernal blue?

 

The spark kerbal is blue. The spark plugs came pre-gapped and I did verify it. I took the breather off and sprayed starting fluid in it and also tried through the plug. It does not even try to fire. I checked the clearance of the valve and it didn't have any clearance so I set them to .006. I verified that it is getting fuel to the carb and it has spark. I ran all new wires and grounded and verified the ground to the coil pack by checking the resistance to the frame and battery.

 

Good info. It should have gave you a pop. If there was nothing, you've narrowed it down spark timing, valve timing or compression.
Check your spark timing. Youll need a timing light.
if its ok
is the plug wet when you tried to start it or was it dry? Did you put a healthy dose of starting fluid in carb? Choke off, hold throttle open, turn engine over spray it in air horn, is that how you did it? If not, pls do.
If that fails to pop or attemp to start....
Do a dry compression test and one with a squirt of oil in the cylinded. If the oil helped helper probably rings or scuffed dinged piston. If it has sat the rings can be stuck in the piston lands.
if the oil didn't help, it's probly valves or valve timing.
Check your crank to cam timing look for marks to line up, while you're there set your valves at .004. Tap the woth a rubber hammer. Do you hear them seat? If you bought a platinum plug buy a copper for diagnosing. Ill try to help you. I suspect timing or compression.