what would cause a 4 wheeler not to start

Check the air filter. Mice like to nest in them over winter. If it's clogged, the engine can't breathe and won't start. Also make sure the choke is working properly. I've seen stuck chokes cause no-start issues after storage.

Spray a little starting fluid into the intake. If it fires and dies, you know it's a fuel delivery problem. If it doesn't, look at spark timing or compression. Don't go crazy with the fluid though.

Definitely sounds like a carb issue. If it sat with fuel in it, the pilot jet is probably gummed up. Pull the carb, clean it thoroughly, especially the tiny passages. It's a common winter storage problem.

Before you pull the carb, check the fuel shutoff valve and petcock. Sometimes the diaphragm gets stuck and no fuel flows. Also see if the fuel line has a kink or crack. Simple stuff first.

Could be a bad ground connection. Even if the battery shows voltage, a loose ground can cause low current. Clean the battery terminals and frame ground. That fixed my buddy's no-start after storage.

Make sure the kill switch isn't in the off position. Sounds dumb, but I've seen people chase electrical gremlins for hours only to find the lanyard clip was loose.

I disagree with the starting fluid suggestion. On some 4 stroke ATVs it can wash the cylinder walls and cause damage. Better to check if the plug is wet after cranking. If it's dry, fuel is the issue.

If it's turning over but not firing, and you have spark, it's almost certainly fuel delivery. Check the carb bowl drain screw. If no fuel comes out when you open it, the float needle is stuck shut.

Also consider the valve clearance. If the engine sat and a valve stuck slightly open, compression drops. Do a compression test before tearing into the carb. Should be around 90-120 psi depending on model.

I had similar symptoms after winter. Turned out the pilot jet was completely blocked. I soaked the carb in an ultrasonic cleaner and it fired right up. Just make sure you know how to reset the air/fuel screw after.

Don't forget the ignition coil. Sometimes they can fail when cold or after sitting. Check for spark at the plug wire with a tester. If it's weak or intermittent, replace the coil.

Could be a safety interlock issue. Check the brake switches or neutral switch. Some machines won't start unless in neutral or with the brake held. A stuck switch can cause no-start with good crank.

If you have a mechanical fuel pump, check the pulse line. Cracks or loose connections mean no fuel delivery. On some 4 wheelers the pump is vacuum operated from the crankcase.

Another vote for carb cleaning. I've revived dozens of quads that sat. Soak the carb overnight in cleaner, blow out all passages with compressed air. Don't forget the tiny idle circuit hole.

Check the exhaust for blockage. Mice or mud daubers can build nests. A blocked exhaust will cause the engine to crank but not start. Remove the muffler and see if it fires. Easy test.

Spark plugs can look good but fail under compression. Swap in a new one just to rule it out. Also check the plug cap resistance. I've seen a bad cap cause no-start with visible spark.

If it's a Honda model, check the spark plug boot for corrosion. They're known for that. Clean it with dielectric grease or replace the boot. That fixed my TRX.

I'd start with simple: fresh fuel, clean air filter, good battery, and a spark test. If those check out, then move to carb and compression. No need to overthink it. Process of elimination.

Make sure the engine kill switch wire isn't shorted to ground. I had a frayed wire that would ground out only when the handlebars were turned. Intermittent no-start is a nightmare to find.

Also check the starter motor itself. If it spins slow even with a good battery, the brushes could be worn. That will prevent good compression on the starting stroke. Listen to the cranking speed.