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Discussion Starter #1
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.
 

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The stator is notorious for grounding out at the black rubber “grommet” as it leaves the case and also shorting at the white connector downstream from that. Search for “loss of spark” or “one spark” and you’ll find what I mean and some possible fixes.
 

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Discussion Starter #3
The stator is notorious for grounding out at the black rubber “grommet” as it leaves the case and also shorting at the white connector downstream from that. Search for “loss of spark” or “one spark” and you’ll find what I mean and some possible fixes.
Thank you. Yes when researching i noticed a lot of people having a similar issue. I didn't see anyone else saying that theirs would occasionally start though. I just finished checking a few things on it. Today it seems to be starting up pretty good, but when revving the rpms up it pops and will stall on occasion. I pulled the carb again and double checked everything, and checked timing, and valve clearance again. Everything I check looks good, except for electrical tests with multimeter. Multimeter is all over the place on everything maybe I'm not using it correctly. Would bad spark or badly timed spark cause the lean popping condition and smell like gas. I'm confused because it pops like its lean, but smells like its rich.
 

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You may have a stator problem then and you’re smelling unburned fuel out the exhaust.
 

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Discussion Starter #5
You may have a stator problem then and you’re smelling unburned fuel out the exhaust.
Thank you, that's what I'm thinking. Guess I'll pull the stator cover tomorrow and try another one I have. I'll let you know how what happens
 

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Discussion Starter #6
Well I put the stator from the old motor on it and have great spark now. One thing I'll just remind everyone is make sure you dont forget to make sure the 2 dowel pins are in the case before bolting the cover on. I missed the dowel pins that stayed in the old cover when I removed it. At first it wouldn't start, and i had no spark, a slight flash once in a while but that's it. I was trying to figure out why in the heck it was even worse now than before. Eventually I noticed the dowel pins still sitting in the other stator cover on the bench. Removed the stator cover on the bike and inspected everything. There was some slight to moderate guaging about half way across what look to be weights on the outside of the flywheel. I smoothed everything out the best I could, I could see where it rubbed on a small edge of the inside of the stator cover. Didnt do any major damage that I can tell. Cleaned everything up, installed dowel pins, gasket maker and bolted the cover back on. Now its getting consistent great spark, at it fires right up, and runs better than it has since I put the motor in a few weeks ago. Does have a lean pop on deceleration, I'm hoping cleaning the carb and opening the fuel screw a bit will help. I'm pretty sure its 2 turns out right now, and my dads and brothers are either 2.5 or 3 with the same dynojet setup, this one has.
 
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