Engine Trouble Oscillating engine noise

Pancho86

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Jan 1, 2024
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Ok quick background, I just put my yd100 on a new frame. Yesterday I rode it to work and no problem, no noise fluctuation, nothing. But when I left it started making this fluctuating noise, that's more noticable at mid range and up. The best analogy to use when describing the noise would be this: imagine a taught wire, guitar string makes more sense, and you pluck it and it starts vibrating but as the energy fades the tone from the string makes almost a warble, rising and falling. It's that. I'm not real familiar with sound wave terms, but if you could see the sound wave they would be short in height but long in length. Im sure someone out here will understand that. Also worth mentioning is I run my mix at 50 to 1, but on this "gas can issue" I'm running seafoam through the system to clean out the cobwebs, I noticed there's still some carbon buildup on top of the piston from when I was running it too rich when I first built it. But this is my second tank of seafoam added gas.
Any help or ideas would be appreciated.
 
Could be a resonant noise in the frame or really anywhere.

You want some carbon on engines, I call it seasoning, this carbon works as a buffer, unless you have carbon pebbles coming out, don't bother.

As Amwicr said, mix 32:1.
 
I've had that sound come from the head gasket. Retorque head bolts.

It must have been running a little slower.
 
Yeah just a wee bit slower, this motor doesn't like anything stronger than 40 to 1, any more and it starts burbling and bogging. Yeah I actually bought all new heavy grade nuts bolts etc. when I did the swap. And I torqued everything down real good last night. I was even thinking about an intake leak, so I'm definitely looking at the head, might be worth changing the gasket anyway. And when I get off work I had planned to drain the tank and go back to my regular gas minus seafoam.
 
Yeah just a wee bit slower, this motor doesn't like anything stronger than 40 to 1, any more and it starts burbling and bogging. Yeah I actually bought all new heavy grade nuts bolts etc. when I did the swap. And I torqued everything down real good last night. I was even thinking about an intake leak, so I'm definitely looking at the head, might be worth changing the gasket anyway. And when I get off work I had planned to drain the tank and go back to my regular gas minus seafoam.
No need to replace the head gasket,, just retorque them. During your breakin period you're gonna need to retorque them after every heat cycle
 
If you have had the head off, some times from the factory the head is torqued down uneven and the gasket will be deformed and not seal well. Something to look into, I've sanded them flat before and had them work. Not ideal but keeps you mobile until a new arrives.
 
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