https://youtu.be/-nEePcFnZ44?si=Y2eEVp9JmfSuspt7

https://youtu.be/cgyevs_LAAg?si=KuZT17PpDxx6qKJJ

First post, sorry I don't really know what I'm doing posting. Hoping the video links to YouTube work to show what's going on.

'83 K100. Assuming something electrical going on. I spent 5 minutes trying to start it before this. I'd hit the ignition and the taco would just flip out, starter would not engage. The few times it did it would fit/flip out then stall.

This was a very intermittent issue at first with very brief cut outs while riding, then it gradually became very prominent to the point where it won't start.

Is there a known issue that causes this behaviour? TIA

Let's go for the simple bit first: pull the HT leads and check for copper carbonate (green stuff) on both inside the plug leads and inside the coil towers. When you switch on, it's pretty much a given that one of the plugs will be in the firing position and if the leads are corroded, it produces all sorts of funnies. Although early coils are prone to cracking and shorting, I'm not willing to point you down that route yet. You can, however, try the whole sequence in the dark and see if you are getting blue sparky bits around the coils. The tacho is playing stupid because something down in the coils is playing stupid. It's driven from coil 1-4 (the forward one).

I'd hit the ignition and the taco would just flip out, starter would not engage.

What does this mean? Starter whirrs but does not engage??

You've posted in Forum Functionality, which is not even remotely where it should be, and is a real bugger to move to the correct forum section. The original poster ought to be more selective in future, and should've used Electrical Troubleshooting.

Calling RickG if you're healed enough to look into it. Ta.

Something else, I don't feel confident about the coil for cylinder's 1,4. Does it make a buzz sound, or a buzz disappears when it's primaries are unplugged, or a buzz from the relay box? 

It might be sneaky enough to pass the coil tests, since it's intermittent, but if the coils are swapped, the tacho problem might disappear.

Actually since it took a while to start, maybe it's only intermittent when it's warm, and the coil or coils do fail simple tests when cold.

On the tech page of this forum is a troubleshooting part that describes how to test the coils.

Two Wheels Better wrote:You've posted in Forum Functionality, which is not even remotely where it should be, and is a real bugger to move to the correct forum section. The original poster ought to be more selective in future, and should've used Electrical Troubleshooting.

Calling RickG if you're healed enough to look into it. Ta.

All Done

I forgot to add, let's say tomorrow morning, with the engine cold, it again takes five minutes to start, this would be a good time to make some checks. One easy thing would be to put a timing gun on the high tension leads to see if one or more of the plugs isn't giving sparks, or missing sparks in time with the engine missing.