I didn't believe until it happened (spark plug under compression)

angus67

Welder's penetrate deeper!!
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So I've been racking my brain on this 80xs I'm trying to sell.
130 comp on left side, erratic firing
Carbs are clean, checked valves, for fun I checked timing . Switched plug wires side to side to see if problem followed, nope. Check spark with plug resting on fin, bright white spark. Dancing with idle mix, messed with the needles, bore scoped the cylinder, took off plug cap and gave fresh end, still crappie. It was just getting worse.
Tonight, I was almost resolved to pulling the carbs again to clean the pilot. The right happily firing away, dragging the left on its 4 strokes.
Racking my brain I tried to think of what else I can check without pulling the carbs, if I had my comp gauge set, I do hook that up and listen for a hiss, but a buddy has it.
AHAHA!!!!!
I had heard tale of plugs that won't fire in the hole, but shine brite resting on the fins. Using the same plugs, I switched them side to side. F-re fired right up, again, the right sputtering erratically, and WHAT? THE LEFT FIREING AWAY? Almost a smooth idle. So I grabbed the ap63's out of a different bike, and,,,,
Al be it a little ruff, but fireing contuisly. I let it idle for a bit, still maybe a miss every 5th hit, but I haven't messed with that mix screw. I'll call it a victory, and head inside for dinner!
What makes a plug do this? I've never had this happen.
Whenever I had issues with non firing plugs, I just hit them with a brush and carb cleaner, and back to life.
I'm a believer now, I was skeptical.
Tomorrow, mess with that mix scree, try to smooth it. The right side has 150 comp, left 130. I know the left will be tricky, but made a big hurdle tonight.
 
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Found out last week the guy really interested in, baught a different bike. I just couldn't figure it out fast enuf.
Got around to test ride it today. Flawless. Strong pull, clutch set perfect..
 
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