Mystery backfires/ignition 180 out???

atom4488

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Greetings to the crew,

Installed a TCI motor in a non-TCI chassis. Used the TCI box, the original points-type coils and tested the ignition system; bright blue spark on both sides, timing at cranking speed right on the "F" mark, so all appears to be in order.

The engine will not start. It backfires in the pipe and in the carbs, to the extent that it blows the carbs right out of their spigots. It appears as if the timing is 180 degrees out, but I can't see how that is possible with a wasted-spark system. So maybe it is something other than 180 out, but what and how?

Hoping for some brilliant insight that I have not considered; what could I have overlooked or messed up in my installation?

Brgds,
 
No experience on Yamaha TCI
But on Boyer Bransden there are 2 coils in the pickup that riggers the ignition If by mistake flip those wires the ignition will be off.

Not sure that is possible someone else Chime in

the original points-type coils
 
Well the TCI is a single coil system how'd you wire in two coils?
Double check the key is still in the rotor crankshaft taper.
picture of the rotor stator area?
Late iggy diagram (2).JPG
 
Hey gggGary,

Thanks for chiming in. The TCI box simply has two outputs going to the TCI coil; power and signal (or trigger). I simply wired splitters for the single outputs from the TCI to the two non-TCI coils. Very easy for me to temporarily install the TCI coil, as all I am doing for now is shop-testing. Why though would this make a difference?
 
If you are firing both coils together ( about the only thing you COULD do) you may be stressing the TCI.
Combined in parallel about 2 Ohms compared to the TCI coil's design of 2.5 ohms As ohms drop, draw increases.
Do you still have the condensers in the circuit? Not needed, desired.
1656104361543.png
 
Ohm out the pick up coils they should both be in the neighborhood of 700 ohms; disconnected at the plug either orange or gray to black, infinity to ground.
Damaged, worn, broken insulation, wires nearly broken off, pick up leads in the sprocket area is not rare and can lead to very flaky ignition.
 
I would be careful with this ---sit on the hands ...for a while till someone else cones in
Again this is an older ignition . I dont know much about ..For newer ones it is of importance having the right power ind and resistance ( Impedance )
in and out
You can risk fry the TCI box and those can cost a bit.
There is probably a transistor on the box output if coil resistance to low there can be an over current.
 
If you're certain the timing is correct, it's possible the box is bad. I have one on the shelf right now that backfires up a storm and won't run... just like what you're experiencing, so that's always a possibility.
Agree with others... no tellin' how the box will react to two coils in parallel. You should really use a single coil to at least eliminate that as a possibility.
Have you ohm'd out the pickup? Should have 700Ω on each coil and 1400Ω across both... or thereabouts.
 
Many years ago, when I was starting a career as a project manager in the aerospace industry, a very senior client (a senior officer in the Dutch Marines) gave me a detailed explanation of master schedules. In that explanation, right before the final acceptance of the equipment, was an activity labelled "PFM". It was of course a trap, wherein I was expected to ask "what's PFM"? So I did... and so I was told that's where "pure f'n magic" occurs!

Guess what? Installed the TCI coil and PFM occurred. Bike starts and runs more or less normally. Bit of tuning required, but otherwise good, no backfires. I still cannot understand specifically why, as timing was spot-on with the dual coils.

As usual, thanks to all who have provided input!
 
Guess what? Installed the TCI coil and PFM occurred. Bike starts and runs more or less normally. Bit of tuning required, but otherwise good, no backfires. I still cannot understand specifically why, as timing was spot-on with the dual coils.
Not all coils are equal. They may ohm out the same, but they're coils... could be they had a slightly different discharge rates. Could be some sort of ring state 'tween the two... who knows. Glad you got it sorted.
 
Look for a used Honda MP08 coil on Ebay. They make an excellent replacement for the original TCI coil.... which ain't no spring chicken at 40+ yrs. Plus you can swap out the leads on the Honda. You can't on the TCI coil.
 
If you can get hold of a Honda CBR600 coil it makes a great replacement for the TCI coil.
I managed to get a pair myself on auction really cheap a few weeks ago.
Quite a few other Honda bikes use that coil too, It's got 'MP08' stamped on it.
There are some threads on here about it if you do a search.
Edit... Whoops Jim, you beat me to it :D
Honda-MP08-Coil.jpg
 
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