Derbi Senda 50 won't start - timing ?

[dommylove]

I have got spark (jumps 8mm outside engine), strong petrol vapour smell, wet plug and compression is 100psi. But it still won't start (kick or bump). Crank uses a woodruff so cannot be set wrong.
I am struggling to understand how the stator pickup works. The flywheel has an internal magnet and pickup is inside, so how does the pickup no when to tell CDI to release spark? Its a Ducati flywheel.

All other rebuild work done (inc main bearings) so this is uba frustrating.

[jaffa90]

(jumps 8mm outside engine),
Does that mean the spark plug gap of 8mm sparks?

[BenR]

100psi compression sounds very low to me is it still a 50?
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Current bikes: suzuki RG125UN wolf. Yamaha MT-07

[Robby]

It's a 2 stroke 50cc, so 100psi is fine.

You have fuel, spark and compression. By the sound of it you're had the engine in bits. Work out which bit you assembled wrong, don't look for a problem in something you didn't touch.

CDI ignition in a nutshell. Magnet on the crank goes past sensor. Sensor sends a signal to CDI box. CDI box sends a signal to coil. Coil sends lots of electricity to plug. Spark happens.

Timing is generally fixed, although on some bikes it is possible to put the crank trigger on upside-down and put the timing out by 180 degrees.

If it's the first start after a rebuild, I tend to not use the choke or throttle and keep cranking/kicking it over until it coughs, then use choke to try starting it.

[Hong Kong Phooey]

Have you checked the Woodruff key hasn't sheared?
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'81 CG125, '97 FZS600 : '99 CBR600F4, '09 KTM RC8