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powerband knocking

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a while back i noticed that my engine was knocking once i hit the powerband. i took it to the dealer for them to check it out they said that it was the exhaust coming out of the cylinder. they said that the pipe wasnt sealing properly but it wasnt a problem. so i rode it for about a week then it blew up!! i rebuilt it took it for a couple rides to break it in and i noticed that its still making that noise. so is it just the exhaust or is it a bigger problem. i really dont wanna have to rebuilt it again. thanx for any info

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Can you describe what your motor looked like when you took it apart? The condition of the piston/cylinder/head??

It will help diagnose the problem.. Sounds to me that you're detonation (pre igniting) and might need a richer needle setting or richer main..

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If you have the tool to remove your stator, remove it. See if the crank shaft wiggles. May be crank bearings.

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+1 on what bikedude said. If your exhaust pipe isn't sealing at all, it will cause jetting problems. If it is leaking out of the cylinder / pipe connection, replacing the o-ring is a really easy and cheap fix.

If it is true detonation, then you have a jetting issue (could also be bad gas). But, don't chase jetting until you know that the cylinder / pipe is sealed properly, and repack your silencer while you are at it.

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+2 on Bikedude. Sound lean to me. Rich bikes don't blow up.

Actually I will put myself out on a limb here. Too lean on the main jet is my thoery

based on the info given. Sounds like it is pinging under 3/4 to full throttle, right on the main jet.

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yep theyre all right, could be with the colder weather your jetting is now too lean. go a size or two bigger on the main jet, and see if it still knocks.

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yep theyre all right, could be with the colder weather your jetting is now too lean. go a size or two bigger on the main jet, and see if it still knocks.

Bingo.. Its fall/winter time and the air is cold and sometimes wet.. Time to think about winter jetting.. I had to go richer on my needle and pilot a few weeks ago, and think I wanna try a half clip richer on my needle still... Good luck OP :bonk:

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when it blew up it was in august so it wasnt the cold weather and it was starting to knock then. when i took it apart i the top of the piston looked good but the piston skirt on the intake side broke off in to little peices and fell in to the bottem end so i had to split the case and clean it out. i checked the seals and bearings they were good the bearings moved free and easy and the seals didnt have a hole or cut in them. the cylinder and head were still brand new. when this happend it was a brand new bike there was only 15 hours on the bike. and it cant be the gas bc there were 2 other guys that i lived with all had the same bikes and we used the same gas. im really stumped haha ill check the o-ring on the pipe that connects to the cylinder

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when it blew up it was in august so it wasnt the cold weather and it was starting to knock then. when i took it apart i the top of the piston looked good but the piston skirt on the intake side broke off in to little peices and fell in to the bottem end so i had to split the case and clean it out. i checked the seals and bearings they were good the bearings moved free and easy and the seals didnt have a hole or cut in them. the cylinder and head were still brand new. when this happend it was a brand new bike there was only 15 hours on the bike. and it cant be the gas bc there were 2 other guys that i lived with all had the same bikes and we used the same gas. im really stumped haha ill check the o-ring on the pipe that connects to the cylinder

It could be lean jetting or an air leak causing lean jetting. What do you have now? What do you mix your gas with and what ratio? If you only have 15 hrs on the bike then it's likely not worn out reeds.

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im new to workin on bikes i had help when i tore it apart i know ur talking about the carb when u say needles and air screws and that but i dont know what they really are haha...

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Air screw is next to the idle screw (the one with the spring), kind of by the air boot. The needle is found after you take the slide out by loosening the 2 clamps of the carb, turning it so the top is facing you and taking out the 2 top screws. The slide then pulls out and the needle can be seen (the thing at the bottom of the slide). To change the clip position you have to detach the throttle cable from the slide then use a 6mm socket to unscrew it.

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i just realized that when i rebuilt it i never got it properly timed right. im guessing thats it?? ill get that done and see how it works.

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i just realized that when i rebuilt it i never got it properly timed right. im guessing thats it?? ill get that done and see how it works.

I'm not sure what you are referring to when you say, "timed right" Its just about impossible to mess this up if you're doing a top end job.

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i replaces the o-rings on the exhaust it still makes that noise but not a bad. i noticed that there was exhaust coming out of the over flow hose on the cylinder. should that be happening??

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