Ty250A Throttle/kill Assymbly Innards: Kill Switch Kaput.

[motosolex]

Hello all.

The electrical portion on the throttle/kill assymbly on my restoration TY is finally beyond repair. The post and contact slider are disconnected.

Anyone have the innards they want to get rid of so I can reinstall them in my housing or know of a source for these parts or a place to have it rebuilt?

I could always put an after market kill switch but I love the classic look of this bike. I found a source on e bay that sells the black thumb switches so I feel I can manage this off.

Thanks!

[Tillerman6]

TY 250A wiring myths solved!.

There are three ground points used in the TY250A wiring that are important for the spark ignition system.

At the source coil- inside the magneto- one end of the source coil is grounded to the frame.

At the High voltage Spark coil- one end is grounded to the frame.

And at the kill switch- If you slide the kill switch to the red position it grounds out the primary input side of the high voltage spark coil and the output of the magneto.

And since both coils are just copper wire, the resistance measurement is very low. You might think you had a short to ground somewhere if you had only a garden variety ohm meter to work with.  - For instance, if you measure resistance to ground at the output of the magneto (female black wire) - there is hardly any difference between the readings for engine "kill" and engine run.

(Even with the points held open)  you will get about 0.1 ohms in kill position and 0.75 ohms in the run position !

But the bike was designed that way and it runs fine if everything else is in working order.

 

And since the two coils are in parallel electrically, the two of them together is lower than either one separately.

So on my bike, the two coils in parallel measure just three quarters of an ohm.  You need a pretty good volt-ohm meter with a low ohms range to even be able to measure that.

And that reading is taken with the points open and of course the kill switch sett to 'run" (not showing red}

FYI- on the 74 model there is no blocking diode in the system.

 

 

 

 

 

Edited May 6, 2020 by Tillerman6
TY 250A wiring mystery UPDATE!

[Tillerman6]

So to answer my own question about the TY250A ignition- years later, but better late than never. It's relatively simple.  There are only two coils that matter for the ignition. One is the large left hand single winding inside the magneto, and the other is the High voltage coil which is tapped with one side to a short number of turns leading to ground.  Above the tap, there are a large number of turns that develop the high voltage for the spark. Both coils are in parallel,  and one end of each one is grounded to the frame, so the resistance to ground is VERY low.  When the tapped side of the HV coil is hooked to the source coil, the total resistance to ground is about 0.75 Ohms.  That is measured with the points open and the kill switch set to run (also open).  The magneto (source coil) provides the inductive kick at a very low voltage, and lives inside the flywheel. 

Physically the ignition wiring is fairly simple, and since I am not running any lights, I am only going to mention the ignition wires specifically.

Over the years it looks like my wiring harness has seen some changes.

In that regard there is one area that I had to remedy to get the bike to run.

That was the area between the Magneto output and the input to the wiring harness.

Unfortunately both of these wires have a female connector on the end.

So I took a small male-to male jumper I had left over from the headlight installation and jumpered the Magneto output to the female black wire leading to the HV coil primary tap.

The other leg of the Y comes in from the kill switch.

There is another black ground wire in the harness with a male on the bottom end nearest the magneto.  The top end of it leads to a ground lug which is thru-bolted to the frame.  I just taped it off near the magneto end, as I am not using it.

If anyone has any questions- fire away!