1974 850 commando trouble SOLVED

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Assuming the system you have is replicating the Lucas coils, you might wanna test even the new coil. Primary resistance (between the the + and - terminals) shd be near 1.7 -2 ohms.
Secondary resistance (between either post and plug wire terminal) around 5100.
I say this having bought a brand new Lucas 17M6 in the original box that was no good.
 
krullbeast said:
thanks andy! i will replace my bad coil first and hope that was the problem, but i can see how that throttle spring issue would be baffling if i didn't fully remove it. i think i'm going to cap off my choke after this. i just doesn't seem necessary, what do you think?
Click to expand...
Lee
Good to hear you're getting sorted.
Concerning the choke, I guess it depends as much as anything on how quickly the engine warms up and the related ambient temperature. If the engine usually warms up quickly then you'll be fine without the choke.
Here in the UK I find I need to use the choke in colder months, particularly as the route out of my village is a long steep downhill with not much chance for the engine to warm up.
Plenty run without the choke slides and blank off the holes in the top of the carbs without any problems.
So the answer is...it depends.
Andy
 
thank you all for helping me diagnose my problem. it was the ignition coil! another thing to break and learn from. i love my Norton and i appreciate you all helping me out in my time of desperation, hahaha. i'll be smiling until the next thing breaks! on to the next one, on to the next one. be careful out there!
Lee
 
Thanks for reporting back. And are you saying that a new coil from Tri Spark had failed? How new was it? Was it a single unit with double output, or what?
 
Mr. Rick said:
Thanks for reporting back. And are you saying that a new coil from Tri Spark had failed? How new was it? Was it a single unit with double output, or what?
Click to expand...

no, i bought them on my own from steadfast cycles. including the new one i just installed. there is a chance that the coil failed due to overtightening of the bracket, but it wasn't cracked and didn't get hot??? but the problem was definitely the coil. new one works great! single output
 
At one time CNW was not offering warranty on TriSpark ignitions if they were run with stock coils. I do not know if this is currently the situation. But from different conversations here it was decided that it was possible to have a coil that offered the required resistance but still offer too hot of a spark, thus burning out the unit prematurely. This hot spark theory was not proved by any testing but was what was left as a theory when all the others were found wanting.

https://www.accessnorton.com/NortonCommando/trispark-warranty.15121/
 
rvich said:
Its a good idea to swap the coils, not just wires and plugs.

If you are running stock coils its a good idea to get rid of them due to compatibility issues with the TriSpark.
Click to expand...

You can get longer spark plug wires (I have some for troubleshooting purposes) and have a wasted spark ignition you can swap wires so the the right coil fires the left cylinder. If the problem doesn't change sides it's not an electrical issue.
 
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