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

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Old 10-30-2019, 05:18 PM
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Join Date: Aug 2019
Posts: 117
Default 18 XC300 possible detonation

Hey everybody I have an 18 XC300 that I recently had to rebuild. I had a leaky left side crank seal that caused a lean condition and melted a hole in the piston. I just finished the rebuild and I am noticing what to me sounds like some detonation at about 1/8 to 1/4 throttle when holding it steady. I also notice it every once in a while when chopping the throttle. It is just a singular knock. I currently am running with an RK tek head supposedly set up for 91 octane, lectron carb which is adjusted slightly rich with a 4-2 metering rod. I am really paranoid and don't want to have to rebuild my motor again and am kind of lost on what to do other than run race gas which I havent tried yet. Is this possibly caused by ignition timing? I didnt see a way to easily change timing on the bike and there is nothing in either manual about it.

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Old 10-31-2019, 10:07 AM
Greatdane Greatdane is offline
Join Date: Oct 2018
Posts: 18

Did you use a thinner base gasket when you did your top end? I pit the thinnest base gasket available in mine to boost low end grunt, but noticed a slight occasional detonation when letting of the throttle.
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Old 10-31-2019, 11:43 PM
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Join Date: Aug 2019
Posts: 117

The gasket kit I ordered only had one base gasket and I am unsure of the thickness but it was the same as far as I could tell as the original one I removed
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Old 11-01-2019, 08:44 AM
arminhammer arminhammer is offline
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Join Date: Jun 2011
Posts: 185

Pipe bang is a rich condition not a lean one.
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Old 11-01-2019, 10:24 AM
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nknudsen nknudsen is offline
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Join Date: Oct 2012
Location: SE Minnesnowta
Posts: 716

I've had detonation like sounds on deceleration before. I tried jetting, needle position etc.. It ended up that the slide was set too high with the idle screw. Moral of my story is get the bike to idle with the slide as low as possible.
2000 EC250 with 2011 transformation kit, KYB SSS forks, MN street title
16' Ski-Doo XS Renegade X 1200 4T
16' Specialized Fatboy trail
02' ZRX 1200r R.I.P.
72' Olds 500ci, Batten Heads, Street/Drag car, former CarCraft magazine centerfold (has-been)
15' TW200
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