GY6 Compression issue (I think)
Hey everyone, I’m losing my mind with this GY6 build and need some outside perspective. It’s a 2011 Peugeot scooter with 15,000 km on it.
How the problem started:
The scooter began intermittently refusing to start, then one day it just died at low speed while riding. I figured it was the carb, so I pulled it apart and cleaned it pretty thoroughly — but honestly I’m not 100% sure if it’s working correctly now or if I missed something.
After that I started doing compression tests and found something weird:
• Electric starter: ~85 psi
• Kickstart: ~125 psi
Same engine, same gauge, completely different readings depending on how I crank it.
What I’ve done trying to fix it:
• Rebuilt the cylinder 5 times. Each time making sure it was properly honed.
• Wet compression testing kept showing higher values than dry, so I kept thinking it was the rings.
• Eventually bought a brand new cylinder — same results.
• Tested the valves for sealing by pouring water over them and checking for leaks — they held up well.
• Checked valve clearances — set at 0.1mm, which should be within spec.
• Wet vs dry compression gap is still there no matter what I do.
At this point I’ve spent way more time and money than I ever expected on what started as a simple no-start problem.
Why I’m doing this myself:
A mechanic quoted me €250 to fix it — the whole scooter only cost me €350. So paying that feels insane, which is why I’m deep in the DIY rabbit hole. But I’m starting to wonder if I’ve been chasing the wrong problem this whole time.
My questions for the community:
1. Is the difference between electric start and kickstart compression readings actually normal on a GY6? Could this just be a cranking speed / valve timing thing rather than a sealing issue?
2. Could the carb still be the root cause of the original dying and no-start symptoms, and I’ve been going down the wrong rabbit hole with compression?
3. Is 125 psi on the kick actually within spec and I should stop worrying about compression entirely?
4. Where would you look next given the original symptoms — intermittent no-start, then dying at low speed?
Any help is massively appreciated. I feel like I’m going in circles and just want this thing running again. Thanks in advance