Dung dung sound at low,,,,loaded rpm

BucKat

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#1
Not sure what's causing this..

At low rpm ,,,,, throttle chopped,,,,with the engine loaded as in going down a hill with the throttle closed,,,,,, I get this terrible "dung dung" sound coming from the engine....No ,,,not the pipe,,,the engine.

Can't be good.

Help..


Buc
 

BucKat

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#3
Piston slap....most likely not.
KIPS..............absolutely not.


It sounds like,,,,,,,,now I'm guessing here,,,,,,,,, detonation.

It's a real hard DUNG,,,,,Dung,Dung...


It is a DUNG sound not a knock or a ping sound.


Buc
 
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BucKat

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#5
Well,,,I have read a lot of posts on this and several other sites.

Conclusion...Knocking due to either:

1.excessive carbon on top of piston or on cylinder head.
2.poor fuel or too low of an octane rating.
3. bad bearings etc.... possible in my case but highly unlikely.

I will pull the top end apart and have a look. Drain the tank. Refill with new fuel and test on the weekend. I do use premium 93-94 grade fuel.
I will mix at 50:1 and jet accordingly ( instead of 40:1)..May help..may not but that's the route I choose to follow regardless.

Results posted soon.

Buc
 

jaguar

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#6
Could be a reverberation you're hearing from a loose part that's vibrating.
For instance one of my exhaust pipe springs was resting on the pipe and causing an annoying sound so I wrapped half of it with duct tape and that cured the annoyance.
 

BucKat

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#7
Nope...

This is a very definite,solid DUNG coming from the combustion chamber.

It only occurs when the throttle is closed and the engine is loaded..
For lack of better description....the sound occurs during engine breaking..if a 2 stroke could.

Buc