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 HELP solving issues with Yamaha c3 after big bore kit instal 
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Joined: Mon Aug 20, 2018 1:28 pm
Posts: 1
Post HELP solving issues with Yamaha c3 after big bore kit instal
High level - Installed a big bore kit and a new cylinder head, as well as a new variator, and a higher gear. I watched these videos to do to the job:

The job went well, and putting things back together was tough, but it went OK. I started up the scooter, and I’m having some issues:

Major knocking sound (video: and doesn’t want to stay idling unless I keep the throttle on. When you give it gas the noise quiets down, but it stutters.

Engine code (video: 4 long, 2 short

Things I’m concerned about:

Timing & cam install - would timing cause noises like this? I didn’t check the timing at all, though I did make sure the tick on the sprocket was lined up with the case. BUT, when I took it out, the guy in the video said make sure the tick is pointed up?, but I didn’t really understand what he meant, so I’m wondering if the timing is off?

Valve adjustment? I didn’t check or adjust valve clearances on the new head, It had them all ready to go, and I assumed (like spark plug gaps) that it was OK?

Exhaust did not want to seat on the new cylinder head to my satisfaction (there’s a large copper washer in the old cylinder head that I assumed needed to go to the new head, so I put that in, and the exhaust seems like it’s seated up in there, but the flange on the exhaust doesn’t seat up against the casing of the cylinder head.

My reason for saying this is that it might be exhaust leaks? It sounds more hard knocking, rather than a puffing, but I thought I would mention it anyways.

Thanks for reading, please let me know if you know anything about what’s going on, and if you can help me diagnose.

Mon Aug 20, 2018 1:29 pm
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