Flat Landed and Now it Won't Run

[who_gives_a6]

Took a jump 4th pinned in the neighborhood of 70-80ft and overshot by a good 15ft and flat landed HARD. The shocks luckily saved me but barely. But it started sputtering as soon as it hit and died. Now when I try to start it'll fire right up but as soon as the starter stops spinning it'll die. Also I'm getting flames/backfiring out the exhaust now. I've never even heard it backfire before and the plug is always a nice brown color.

I checked the fywheel and it's not spun, have went through grounds and all electrical, replaced coil with a known good one, etc. Still the same. Instantly fires but dies as soon as starter stops. Getting plenty of fuel too. This quad has worked flawlessly since built but this has me stumped. When I say I hit hard I mean hard. Surprised nothing broke in the suspension, axle, or anything like that. Good ol Fox Float RC2's.

Any ideas what to look for next? What would cause it to fire easily but die without the starter engaged?

[who_gives_a6]

Both injectors are good and spraying as they should too when I look down the intake.

[Canniboomer]

Flywheel maybe not spun on itself since you checked for that,
but perhaps the key is sheared?.... the C on flywheel should be at 12 oclock with piston rotated to TDC.

[yamadjs08]

QUOTE (Canniboomer @ Jan 25 2015, 09:20 PM) <{POST_SNAPBACK}>

Flywheel maybe not spun on itself since you checked for that,
but perhaps the key is sheared?.... the C on flywheel should be at 12 oclock with piston rotated to TDC.

Agreed. Definitely sounds like the flywheel is out of time.

[who_gives_a6]

It's running now but I don't understand this. The flywheel was not spun and the key wasn't sheared. I decided to swap the flywheel with a spare and now it fires up and runs as it should. Seems like that did the trick. I just don't understand how the other was bad. Maybe the insanely hard hit and me being on the throttle/the sudden stop caused it. I don't know.

Would it make a difference seeing that it was pinned? I can't see anything wrong with it.

[MX Quad Dad]

Did you check the wires that go to the stator? in the area where they go under the flywheel.

with it running move/wiggle wires and connectors to see if it dies. also check all grounds

[yamadjs08]

QUOTE (who_gives_a6 @ Jan 25 2015, 10:37 PM) <{POST_SNAPBACK}>

It's running now but I don't understand this. The flywheel was not spun and the key wasn't sheared. I decided to swap the flywheel with a spare and now it fires up and runs as it should. Seems like that did the trick. I just don't understand how the other was bad. Maybe the insanely hard hit and me being on the throttle/the sudden stop caused it. I don't know.

Would it make a difference seeing that it was pinned? I can't see anything wrong with it.

Maybe the steel hub on the flywheel is bent a little? Making the magnets wobble a bit?

Definitely strange though since the flywheel and key were fine.

[who_gives_a6]

I tried to snap a photo but my phone won't get a clear shot that shows anything. There are a few hairline cracks in the flywheel that wasn't working. Not sure if that's the source of the problem or maybe it bent somehow as mentioned but the new one is working fine.

Have the pinned flywheels caused any problems? That one was pinned, though it has been put through a lot.

[yamadjs08]

Is the C in "cannondale" lined up with the keyway on the flywheel hub?

[who_gives_a6]

It kind of is. I looked at it and compared it to another and it does appear to be a tiny bit to the right of the C. It looks lined up at first but it's a little off unless my eyes are playing tricks on me. Can't see that causing it to be that far off on timing.

Never spun a flywheel before or seen one spun. Figured if it was spun that it'd be way off.