cb 125 rsd wiring problem

[gwgw]

Hi everyone, quick simple question for all you experts. I'm confused why my bike won't start. When i connect my voltmeter lead to the + on the coil and other lead to earth/frame i get zero volts. [ign on or off].
I have been following the 125 rs diagram [kindly uploaded by caferacer843] which is exactly the same as mine.
Am i correct in thinking i should have a 12v supply to coil ?
Basically i just want to start the engine to see if its running ok. All i want are the basic connections to just fire it up, ie battery, points , coil, condenser. All other components are disconnected, such as the lights, horn, resistor, regulator/rectifier and alternator.
The coil reads 4.7 ohms accross the + and - ?
Before i delve further could anyone confirm zero volts at coil and i am ok to leave the other components disconnected or could this be the problem.
Many thanks for looking.

[unitynotsocri...]

no power to coil....or bad earth checkpoint........
usually theres no power to the coil unless the cdi unit allows it.The cdi unit turns the power on and off to the coil?
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nearly a normal tax paying tosser.......with ferrileness suzi100,cg125,cb125scb100n,cb175,cd100,cj250t,kh250,c15,125 bantam,super 6,rickman gs750,xt500,250rs,dt175,lifan125,dolomite1850,metro,Morris220ld,morrisfg,leyland princess,range rover,corsa,vw camper .now struggling with legs. MORE ORDER = MORE CHAOS

[ricklincs45]

Try connecting both the rectifier and alternator - have a 125 RS myself and can't imagine it'll run without at least the alternator.

You're fine to leave horn/lights disconnected.

Not sure why you're bothering measuring voltage at moment, have you kicked the bike over to see if the HT lead/plug is sparking?

As previous poster has mentioned, ensure all earths are good.
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Author '80 Bikes, and counting...' Currently getting frustrated with an MZ 125 TS.

[Robby]

Your mistake is attempting to simplify things.

Get everything connected up, then give it a go. You want to see if the engine is running well, so there isn't much point in trying to run it without ancillaries.

[gwgw]

[gwgw]

[ricklincs45]

Ok, I can see where you're coming from, but fairly sure you'll need power from the alternator/rotor to get the engine running, in which case I'd advise also connecting the regulator/rectifier (I'm sure someone with more electrical expertise will comment if I'm wrong).

Connect your alternator and rectifier, don't worry about indicators/horn/headlamp, then try kicking the bike over and see if she'll spark. If she does, brill - if not, start will basics such as checking none of the wires are physically damaged and ensuring all your earth points are perfectly clean. Have come across CG125's in the recent past that have had spark problems; these have been solved by cleaning the mounting points where the ignition coil bolts to its brackets.

If no joy with that, go back even further: check your points are actually opening, if they aren't, the bike will never spark. Also worth removing the HT cap and seeing if the coil will spark (to earth) with it removed.

Trying to make things simple by leaving things like the alternator disconnected is actually making things harder to diagnose where the fault lies.

Good luck


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Author '80 Bikes, and counting...' Currently getting frustrated with an MZ 125 TS.

[gwgw]

Hi again,
decided to run a 12v supply to coil direct from battery, hey presto i got my bike started.

If i reconnect my ign switch and alternator etc, i end up with no supply to coil, i assume from wiring diagram that the supply would be from black/white wire from the alternator. So on kickover would this supply the voltage to coil, if so does this mean my alternator is capput ?

Any simple tests to confirm.

Appreciate any pointers...
Thanks everyone

[unitynotsocri...]

remember ,with the normal wiring ,ANY power to the ignition coil and points is usually routed through the ignition switch,and a few switches have a 'null' circuit,two wires that deliberatly short a power or ignition coil out to prevent the engine starting when the switch is in the off position because the power for the ignition coil is taken from a generator coil,not a battery supply.i.e. stop theives.....

this circuit caused great hilarity with bike theives in the 80's ,intent on killing cg's and other bikes that used a flywheel power coil for points,simply....instead of picking the lock or buggering it with a big screwdriver ,all you did was disconnect the ign switch connector block....VOALIAVOLAI start me and trash me,i dont even need a key!!!!thank you honda.

maybe cg's deserved it for being the ugliest mfkrs,below mz's.

with the advent of chinese clones,the glory daze of stolen cg grasstracking is making a comeback.
____________________
nearly a normal tax paying tosser.......with ferrileness suzi100,cg125,cb125scb100n,cb175,cd100,cj250t,kh250,c15,125 bantam,super 6,rickman gs750,xt500,250rs,dt175,lifan125,dolomite1850,metro,Morris220ld,morrisfg,leyland princess,range rover,corsa,vw camper .now struggling with legs. MORE ORDER = MORE CHAOS

[gwgw]

This would confirm with the afore mentioned wiring diagram, ie, the ignition has to be on to feed the coil.
As i can't make out the colours of the 3 wires coming from the alternator is there a simple way of testing them to determine which goes where ?. Or doesn't it matter ?
One to ignition switch [b/w], one to reg/rec [white] and the other to the yellow wire for the lighting switch.
A 4th wire [light green] goes to neutral switch which is ok.
Thanks all.