No Spark on a TY50

[grotto]

I've got an old Yamaha TY50, mid-late 1970's, points ignition.

Wiring has been modified (no battery, lights, etc.)

I can't get a spark.

It was wired up with the black wire from the engine to the coil, HT lead to the plug, real simple but was it correct? (I don't get a spark).

The points open and close when engine is kicked over.

Using a multimeter there is minimal voltage (under 1 volt) at plug cap when engine is kicked over.

There are 4 wires coming out of the engine;
Black, Green, Yellow, and Green/Red.
There is another wire (light blue) in the same bundle, which doesn't go anywhere but has a terminal on one end which looks like it would screw onto something (maybe an earth?).

I was going to check the stator coils, but had a go at removing the flywheel/cover with a gear puller, but it seems to be on really tight, and I'm nervous about breaking something (I don't have a manual to check if anything other than the nut on the end of the crank hold it on).

I'd like to wire it up without a battery to get spark first of all.

Once I've got spark, if I can get it to run (it's only got 85 psi compression) I'll have a go at wiring in a battery.

The plan is to work on it over the holidays with my kids, and hopefully they'll be able to learn to ride a bike with gears, and gain a bit of hands on experience at bike repairs.

Problem is I'm a bit stumped at the moment as to how to proceed.
I don't have much spare cash, but have plenty of bits and pieces from other bikes around.

I've attached a couple of photos for reference

Hope someone can help!

[CeeBee]

Hi, It sounds like the wire you have hooked to coil is incorrect probably an earth wire. You need a multi meter to determine which wire feeds the coil. If you have no meter you could try pot luck with connecting the other ones in turn. I find using an analogue meter will show deliberate deflections as the coil is delivered voltage only at a timing mark just before TDC to fire the coil / plug, when the engine is rotated. (Best done with the plug out)

[grotto]

When I kick the bike over, I get the following voltages between relevant wires & earth;
Black 0.8 volts
Green 0.06 volts
Yellow 0.15 volts
Green/Red 0.3 volts
Not sure if any of these are enough to power the coil.
All the other small single cylinder bikes I have which go don't have points, so I can't really compare them.

[RDjase]

When I kick the bike over, I get the following voltages between relevant wires & earth;
Black 0.8 volts
Green 0.06 volts
Yellow 0.15 volts
Green/Red 0.3 volts
Not sure if any of these are enough to power the coil.
All the other small single cylinder bikes I have which go don't have points, so I can't really compare them.

Black wire with white trace to coil, and I have used the horn as a kill switch (pink wire on left switch block) Thats how i have my sons Ty80 set up. It still has the original loom but not using it. The bike is really tidy and i have all the lights ,blinkers and road gear put away. Cant damage them if there not on aye lol. I wil have a look at my pares to see if the points wire in the stator is staight black and not black with white trace, Maybe a change different models.
It may have dirty points or a stuffed condenser. My boys wouldnt go once after he drowned it , we had it running after that but next time nogo ,it had rust and dirt on points

great bikes for kids(and there dads lol)