So here is the run down.

First, this forum and everyone on it has been extremely helpful, but I have yet to figure out what is wrong with my son's ATV. I purchased it at an estate auction, and it hadn't been ridden in a year or so, and had only actually been ridden a handful of times. When I purchased it, it didn't have a battery so that was the first thing I added.

I was surprised to find out that it wouldn't start, even after a carb-rebuild. So with parts so cheap for these quads, I bought a brand new carb, solenoid, CDI, and coil - just to make sure I had covered my bases. Amazon had everything for under $40 total.

I just installed everything, and I'm still in the same place I was before: the starter turns the motor over constantly, but it never fires off.

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1. Spark - Yes
2. Air - Plenty, removed the air filter to test, but it was basically brand new when I got the machine
3. Gas - Flowing like the Nile out of the tank, through the inline filter and to the carb
4. Carb - I've installed a brand new carb, and did not adjust anything, but it still did not start
5. Safety Switches - All seem to be working as they should

I've been jumping it off my car to keep the battery fairly fresh.

Quad turns over, starter runs, carb spits air/gas out the air intake (because the air filter is off) but there appears to be almost zero compression - doesn't even register on my compression tester. I've checked and re-checked the wiring and the safety switches, and all seem to be good - and as I understand it, the starter shouldn't even fire if one of them is tripped. Even sprayed starter fluid into the spark plug hole, replaced the spark plug, and tried firing the engine, but it just kept cranking over and over with the starter motor as always.

I'm beginning to think it has to do with compression, but I really know very little about that - tested for compression issues in my car, and other machines, but never an ATV, and never actually had any compression issues in my other machines - all tested fine. But this little quad has almost none, not even enough to move the needle on my tester.

Anyone have any ideas what I do next? If I'm not getting enough compression to register on my meter, then am I safe to assume that's the likely culprit? If it is a compression problem, what are my options?

Any help the community can provide would be greatly appreciated.
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Would be a good easy and cheap to check valve clearance remove the two caps on left motor cover turn motor ccw with 14mm socket look for a mark "T" lined up with cover mark that should be TDC on cylinder head there is 2 covers usually takes 17mm wrench to remove you will find rocker arms need to adjust those to about .004 inch. Could be the problem as these seem to settle in too tight quite frequently good luck

 

If the quad has stood a long time, it could well be a valve stuck open. If you have a massive clearance on one valve, this will be your problem. Also, when checking valves, the piston must be on the correct TDC, on the other, the exhaust and inlet valves are both slightly open so you would get a wrong reading. With no compression, the best way to check is to watch the valves as you turn the crank, when they are both "rocking" you are near the wrong TDC so move the crank one turn to get to the right one. A spoonful of oil or upper cylinder lubricant down the plug hole may free a stuck valve, but you may have to take the head off to free it.

 

As I said earlier, this forum is truly a great source of information.

I haven't had a chance to try either of the suggestions provided, but wanted to say a quick thank you for the very speedy response, and I'll certainly post my findings here. Hope to get to play with it today, my son found out about the atv - which was supposed to be surprise - and is now pumped to ride it. So now I have to figure it out asap.

Many thanks for the suggestions, and I'll reply here when I give them a go.

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