hello i have a 2000 scambler 500 was told needed fuel pump, but testing im having more of a spark issue, i tested stator and have red and rd/white 19ohms, and pick up have 97ohms, yellow yellow/red 5ohms , coil has 6000 ohms without cap, with cap have 11000ohms, checked timing and all is spot on, has new camshaft,rockers,chain, have a spark tester and it will spark but is very random and sparatic, seems to be weak, if try to start with ether sometimes it'll idle, sometimes it will backfire through carb and sometimes it backfires through exhaust, so now we thinking about poss bad cdi unit but there is no test to check, but i was trying to check for voltage from the blue wire out cdi box to coil, thinking the coil should be getting 12 volts to fire, but seems like only getting about .5volts.. can the cdi box be on it way out of is bad causing it to fire it the incorrect time, which would cause the backfires?

 

Resistance figures look good on stator and pick up coil wiring a well as the coil.One thing you can try is to disconnect the black wire from the cdi and see if it runs.If it does then could be a wiring problem in the ignition switch or left control switch on/off section as these both tie into the cdi kill wire.Or rare but can happen is that the kill circuit(black) wire could be shorted out internally in the cdi itself. If pulling the wire doesn't help,then I'd check the face of pick up coil itself along with the flywheel for any dirt build up.Pickup can ohm out ok but if dirty can cause starting problems. Also if the pick up coil is too far from the flywheel this can cause problems. Seems quite a few like this have happened on the 425 and 500 engines over time.Here's what one member found out.Plus he was able to pull start it but wouldn't electric start. no spark to plug when using electric starter - Page 3 - ATVConnection.com ATV Enthusiast Community

 

i have already pulled the black wire, that is when i DO get some spark, if its connected i dont have any spark at all, ive pulled the stator off already, and the flywheel is super clean, and im guessing its a newer one as reading people say the magnets tend to fall off, this flywheel is a sealed magnets are incased within the flywheel itself, the pick up can only bolt on one way. and i cannot find any spec as to the clearance the air gap should be,, the recoil assembly is not even there, just the case housing, and it does have some score marks inside like something exploded at one time,

 

Then that narrows it down to the kill switch,left control switch or the cdi itself.. I'd try to check the switches out first.