Took the bike out today expecting to do my usual ride. Was into it about 10 minutes and it simply stopped running. No other sound, no knock, no ping... nothing just coasted to a stop. Fortunately most of the ride about 1/4-1/2 mile out was mostly uphill so going back as pretty easy.

I removed the plug, it was not fouled, quite clean really, damp too, no spark that I could tell, but it was bright outside where I was riding and could not shade it enough. That's as far as I got so far. So it begs to question, has anybody had issues with an HPI system failing? I know my trouble may be a simple as a loose connector, but while I was emptying my tank so I could remove it to access to the coil and such, gas spilled big time on the floor of my shop, so I have to wait for it to air out....

I finally got a moment to pop the plug again and kicked it over without the lights on, and seen a yellow consistent spark, so I guess I am good with the CDI. So next stop is carb, but the plug was wet....

I did get the tank off to check if there were any loose connections first, obviously all good there too.

Plugs do go bad.  And they can spark outside the engine and fail only under compression. 

I told this story a bunch of times but I learned to never start a race with a new plug.  Sometimes they'd fail after a few minutes of good running.  Champion was worst.  New NGK failed on me too but not as often .  Only one that never did was Autolite. 

Make sure plug is gapped right...  usually 0.020" to 0.024" or so. 

So something out of the orinary happened if it just cut out totaly & rolled to a stopped. Not crank key let go & its gone half a turn out on timing. Unusual but!!.

I agree with MarkT I’ve had some ngk plugs not fire so I have changed to autolite MarkT turned me on to autolite no regrets 

I am subscribed to this thread, but no notifications.... bummer. I am still trying to figure out what is going on with my ride. Working too much gets in the way. Last week I had a notion to put the tank back on and try to kick over. It was in my shop, and since I seen the spark going on I tried to fire it up, just for the heck of it. The first 2 kicks gave me a sputter. So I got really excited and pulled out of my shop to try again and no go, not even a pop.

If it did go I would have been really apprehensive about when it would decide to crap out on me again, so I am glad it didn't.... kinda....

Today I had some time to work on it again so I popped the carb , dismantled it and set in carb cleaner again for a half hour. On reassembly I finished cracking the NOS gasket I put on it at the time of the rebuild. It did seem weak in one spot. Before I put it in the carb cleaner I thought what I saw was a drop of something, maybe the leftover gas/oil mix that fell out of the carb body. When I went to screw in the air mix screw, I noticed it went straight in to the seat with no resistance. So something is missing. I though first it might have been an O ring that got eaten by the cleaner, but looking at the diagram, there is a spring tat keeps the idle screw in place. That's odd I never noticed it before when I took it apart before. I guess I got lucky it did not fall out then, then again... that must have been what I saw, the spring, not the drop of fuel.

So, tomorrow on my hands and knees to look on the floor of my cluttered shop for the spring. I also ordered 4 more carb gaskets from Ebay to help in future tinkering with my carb.

@ RT325 It has an HPI ignition now with no keyway. I haven't checked that possibility. I think something must have fouled the carb somehow, since it popped a couple of times after it sat for 2 or 3 weeks. I am thinking the thick, black aftermarket gasket may have has something to do with it. There was a trace of black residue in one spot or another inside the carb in 2 places. That's the reason I am getting all new gaskets. The new ones look like OEM, but are supposed to be a newer more durable material that does not get brittle over time. They are not black either. The ones I got in the carb rebuild kit were really thick too and not the ideal size. They fit, but only after carefully trimming the littlest bit from the outside edges.