New Big Bore 80cc motor won't start-only backfires through the carby

[ozbloke]

    Hi all, I need some help. I was given a ZX 50 scooter not running, and decided it was my new project. I bought a 80cc big bore kit to suit a standard crank, a new Taida standard crank and oil pump from Scooter Tuning Canada; new - derestricted CDI coil and spark plug lead;magneto flywheel;stator;crank and transmission bearings;19mm carby jetted up; etc etc etc.
I can't get the engine to start! I have checked :spark & fuel, it cranks great, I've even used an electric drill to spin the motor with the ignition "on" and can only get a backfire through the carby. Pulled the reeds out to recheck.  I did find a difference in the position of the magnetic strip for the Pulse Coil on the new Magneto Flywheel, so I swapped back to the original still only backfiring through the carby! I've uploaded the photos of the differences in the flywheels. Can someone point me in the right direction please?

[CROSSBOLT]

Timing?

[ozbloke]

Hi Karl, funny you should bring that up.   What I did was fix all the wiring connections that a previous non-mechanic had done, then I took the plug out and check TDC position of the piston, then checked the new Magneto Flywheel pickup- way out. Reinstalled the old flywheel with the pickup pulse position for the pulse coil spot -on. Checked the air gap for the Pulse coil(none) and made adjustments to the mounting base(drilled) and back of the pulse coil(filed), to get the right clearance; removed  the leaking, brand new fuel filter; re-checked all the fuel and vacuum hoses; and the damn thing started!! I now have issues with the new carby and old exhaust, but she runs.  It Lives!! Thanks to all who had a read. I'll keep adding to the blog as I proceed with changes that are needed.
Chris

[ozbloke]

Tonite, I ordered a new 28mm Keihin style Carby, Manifold and aftermarket air filter to suit the carby. Fortunately with the ZX 50 you can use AF18 Honda parts as the Kymco ZX 50 and others are a copy of the Honda. Hopefully I should be on the road to success. Lucky Cess.   
Chris

[CROSSBOLT]

How 'bout that! Great! Thanks for the feedback!

[ozbloke]

Hi Karl, thank you for your feedback. With your background I'm sure you knew about the Kymco ZX 50-Honda AF18 interchanges. Further on my motor, I'm running the original reed valves; is it possible for reed valves to become noisy? There is a strange rattling type noise from the motor, that appears to be from the induction side of the engine. It starts when the motor has been running only a few seconds. I thought rings first off, but the crank spins freely. Any suggestions? - Chris

[CROSSBOLT]

Did not know about the parts interchangeabilty but not surprised given the history. Reed valves probably do not have enough mass to be noisy opening and closing. Maybe you could post a video with audio of the noise and let some ears guess what it is...

[ozbloke]

Ok I will do that.  - Chris