Hi guys this lower end swap, with new piston and rings, is turning into a nightmare. My buddy bought a used 400 and something shot through the bottom of the case, as he was test driving it after bringing the machine home. He picked up a used bottom end, and I installed a new piston and rings. I made sure valve clearance was good and timing lined up when putting everything back together. Everything went smooth (for the most part) going back together. Got the motor mounted back in the frame, and everything back together. Tried to start it and it wouldn't start. Just cranked and cranked. So I started checking for fuel and spark. Getting fuel, but have an issue with spark. When I hit the start button the spark plug will spark once, and then when I let off the button it will spark one more time. After checking and finding intermittent spark I put it back together for the night, and just before calling it a night hit the start button one more time and bam it fired right up. I left it running and let it idle for about 10 minutes until the fan kicked on as I wanted to get the first heat cycle done. When it was running it sounded great, no ticking or abnormal noises, just purred like a normal good running engine. The next day (yesterday) I went to start it back up for another heat cycle and it wouldn't start. Pulled the plug to check spark and same thing. Intermittent spark, only when i push the start button, and release the start button do I get spark. Put the plug back in and it fired up, but ran about 20 seconds and stalled out. It didn't want to start again for a while, but eventually it did and stayed running for a second heat cycle. Now I'm doing research. I've found this seems to be a common issue with these, but not a lot of answers as far as what it took to fix the problem. I'm thinking the problem is more than likely coming from something that came with the used bottom end, that I swapped over to this bike. So I'm thinking the problem could be one of these things, stator, wiring short from stator, or possible timing chain issue causing the loss of spark. I did try a cdi box, different spark plug, and new spark plug boot or cap. Still having the same issue. It has intermittent spark when checking the spark plug for spark, and will sometimes start, and sometimes stall out or will sometimes stay running at least for 10 minutes which is long enough for a heat cycle. Definitely have a problem that needs to be fixed before we try to go riding with it. I would love to hear possible answers or things I should be checking or looking at. I have another motor I can pull parts from like stator, flywheel, timing chain, parts on the old bottom end that ran good until something cracked the case, which started this whole debacle.