Backfiring wont start 2007 Ninja 250r

[ColeJefferson]

Put fresh carbs on bike and rode it for a couple of days.
Went to start and starter just whizzed.
Looked in portal and bolt holding flywheel had backed off.
I tightened bolt and tried to start the bike but all it does is backfire.
What did I do that would cause this and how can it be fixed?

Thanks

[jkv45]

Originally Posted by ColeJefferson

Put fresh carbs on bike and rode it for a couple of days.
Went to start and starter just whizzed.
Looked in portal and bolt holding flywheel had backed off.
I tightened bolt and tried to start the bike but all it does is backfire.
What did I do that would cause this and how can it be fixed?

Thanks

Most likely the key is sheared and ignition timing is off.

[sickopsycho]

Originally Posted by jkv45

Most likely the key is sheared and ignition timing is off.

Ouch. At least it's turning over and you hopefully haven't bent a valve...

[Ghostt]

Originally Posted by jkv45

Most likely the key is sheared and ignition timing is off.

That's what I was thinking.

More importantly is why did that bolt loosen up? Not a common problem with the ninjette.

I had a similar problem with my EX500 many years ago, the cause was I failed to properly torque the flywheel bolt.

It's an easy enough problem to fit, and cheap as well.

No worries about valves, the flywheel has nothing to do with valve timing, just the triggers on the flywheel, which sends signals to the CDI.

[Triple Jim]

Correct me if I'm wrong please, since I'm in the ignition system manufacturing business, but I thought our Ninjas used non-CDI electronic ignition system. Transistor switched, that is. The wiring diagram shows 12v to the coils, which seems to agree with my understanding.

[Ghostt]

Originally Posted by Triple Jim

Correct me if I'm wrong please, since I'm in the ignition system manufacturing business, but I thought our Ninjas used non-CDI electronic ignition system. Transistor switched, that is. The wiring diagram shows 12v to the coils, which seems to agree with my understanding.

You are correct, my bad. The PreGen uses a very basic set-up.

I'm used to calling the module that, old habits you know.

[sickopsycho]

Originally Posted by Ghostt

No worries about valves, the flywheel has nothing to do with valve timing, just the triggers on the flywheel, which sends signals to the CDI.

*Wipes green off from behind ears*
Yeah, it's connected to the crank, but not associated with timing outside of the pickup mounted on it. Derp.

[Triple Jim]

Originally Posted by Ghostt

The PreGen uses a very basic set-up.

From the 2008+ wiring diagram, the later 250s are the same, 12v to the coil, coil ground switched by the electronic ignition module.

[Ghostt]

The EX-250's igniter uses a very simple advance curve: 2-dimensions, X and Y, with no compensation for load. It's pre-historic, rudimentary.

At about 4,000 or 4,200 rpm, depending on the year-model of the EX-250, the igniter has the ignition timing at full advance (38 degrees BTDC for the older engines or 42 degrees BTDC for the newer engines).

When you roll-on full throttle at about 4,000 rpm you suddenly make the air/fuel ratio much richer. In a modern car or motorcycle engine the ECU knows when this happens and it retards the ignition a bit because richer air/fuel ratios burn faster than leaner mixtures.

Because the EX-250 igniter has no way to compensate for the sudden rich (faster burning) mixture the ignition advance stays way up there at 38 or 42 degrees and you end up with too much of the burn occurring before the cylinder reaches TDC.

Instead of instantly making a lot more power (as you're anticipating when you open the throttle wide) you make only a little bit more. And the engine slowly lifts itself out of the situation.