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Discussion Starter #1
Hello I have a 03 Honda TRX400EX that has been upgraded to a big bore 426. It’s been recently rebuild new cylinder, new piston, new crank, new cam chain, new cam chain guides, new cam chain tensioner (auto), new oil pump, new spark plug, cleaned and rejected carbs to a PJ 42 Main 162 pilot needle 4th slot down. Whenever the engine is under load it makes this funny sound which I’ll link a YouTube video to coming from the left side of the engine. Almost like a timing chain slap but it’s on the wrong side for that. Does anyone have any ideas? I’m exhausted of trying to fix this thing and in need of help. https://youtu.be/vZdWaP-SYNY
 

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Without actually being able to hear it - my first guess would be an exhaust or head gasket leak - second guess is spark knock - you should be running 93 octane non ethanol fuel or 95 octane ethanol blended fuel.
 

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Discussion Starter #3
I am running pump fuel 93 octane durning that video. I am assuming you have watched the video or is it not showing up?
 

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Discussion Starter #5
Someone mentioned somewhere else a compression spring on the cam could be broke making a rattle like sound? Only way to know would be to tear it down though correct?
 
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