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Enduro Engine - 2 stroke Cylinder, Piston, Tranny, Bearings, Clutch, Pipes & Silencers, etc.


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Old 04-12-2016, 09:27 PM
GGRider01 GGRider01 is offline
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Default What exactly does detonation or pre-ignition sound like?

I'm wondering if anyone's got a video of a bike detonating or pre-igniting. Can't find one on youtube.

Ever since I've had the 300, before I ever rebuilt it or changed the jetting, it has always had a low grumble or what I would call a sputter at low throttle openings.. but I've always been paranoid that is it the "marbles in engine" sound everyone describes when talking about detonation. I'm running 91 octane (highest available at pump, roughly 98 octane RON)/non-ethanol fuel. Never done a squish test and no idea what compression ratio the engine is running at.

Hopefully I'm just being paranoid, but would rather be safe than sorry. It is always at sustained throttle openings, except WOT.



Last edited by GGRider01; 04-13-2016 at 12:21 AM.
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Old 04-12-2016, 10:31 PM
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Run some plug chops, your plug will tell the story.

I think there a "sticky" on measuring the squish.... based upon history that test should be the first thing any GasGas owner
should perform.
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Old 04-13-2016, 02:01 AM
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Hmm hard to describe.sometimes referred to as pinking,as in rapid metallic pink,pink,pink.most noticeable when throttle cracked open suddenly from low revs.often followed by much worse metallic,destructive sounds,swearing,and empty bank account
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Old 04-13-2016, 04:08 AM
Capz85 Capz85 is offline
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This is my current problem, sounds like a rattle ing around half throttle under load very noticeable

I've ruined a piston and cylinder and it's still happening l, so I can relate to the swearing and empty bank account
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Old 04-13-2016, 06:21 AM
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RBrider RBrider is offline
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Quote:
Originally Posted by Capz85 View Post
This is my current problem, sounds like a rattle ing around half throttle under load very noticeable

I've ruined a piston and cylinder and it's still happening l, so I can relate to the swearing and empty bank account
Try raising the needle one notch (IE: lower the clip one notch) Doesn't cost anything and it can't hurt . It will richen up the mid throttle jetting.

RB
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Old 04-13-2016, 06:27 AM
Capz85 Capz85 is offline
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Yes I richend the carb and will run 2 0.5 base gaskets this time, hopefully it will improve
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Old 04-13-2016, 06:45 AM
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The chain hitting the subframe can sound like detonation.
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Old 04-14-2016, 12:47 AM
GGRider01 GGRider01 is offline
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Quote:
Originally Posted by barossi73 View Post
Hmm hard to describe.sometimes referred to as pinking,as in rapid metallic pink,pink,pink.most noticeable when throttle cracked open suddenly from low revs.often followed by much worse metallic,destructive sounds,swearing,and empty bank account
Well, rapid acceleration it sounds tits on. It could just be intermittent four-stroking which is prevalent, but not impossible to get rid of, with sustained partially opened throttle. I found a post floating around on the internet from Jakobi (he's everywhere) that suggests looking at the plug under a magnifying glass - metallic specks indicate detonation. Will have to take the tank off and check it out. Got my spark plug wrench in the mail but the freaking clip on the right radiator hose is too close to the plug to allow it to slip on - will have to slide it a bit.
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Old 04-14-2016, 05:14 AM
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Jakobi Jakobi is offline
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Spark plug, piston, rings.. they'll all show signs of detonation if it has been occurring.

But as others have said.. there are a million noises coming from these machines at various throttle positions (on and off throttle). Chain slap can happen under load at lower rpms. Pipe can vibe against the spigots if the o-rings start to go. Plastics can vibe against the body if they have some slop in them. One of my rad braces on a particular bike would jiggle and dance at certain rpm - metalic sound to the max. The powervalve assembly has a certain amount of free play in it to allow it to operate as the carbon builds up on it. Some have had the PV arm vibe where it clears the cylinder. Others down deeper against the cases.

You can try to isolate certain things to see if they only happen under load, under decel, in gear, stationary. Apply pressure to particular areas (ie the pipe/plastics). Visually inspect. Probe, etc.. but generally I live with the bulk of the sounds.

Capz situation is different in that they have experienced cylinder coating failure and then rapid wear again since.
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Old 04-24-2016, 04:09 PM
motopsycho87 motopsycho87 is offline
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From my experience of not cutting the head enough after doing my squish, revs hit a brick wall. The bike just sounded rich as hell, nothing really audible to be honest. The easiest way you can tell is take the head off and look for little bits missing from the head or piston. Or look through the exhaust or plug hole. It's a lot easier to tell pre ignition on a 4 stroke!
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