Heavy knock

hey guys, after riding the bike a couple of times i decided to keep the bike shut down until i can get this heavy knock problem solved. Here's some info to help you guys give me a more informed opinion. the petcock does not look stock, its a simple gravity feed system. a previous owner put inline filters backwards in the fuel lines as well pod filters for the carbs. i really doubt the bike is jetted properly or even synched for that matter. i have two videos for you guys one of the bike at idle and knocking and the other of the bike revving with no knocking noise.





actually you can hear the same noise come through 4-5 seconds of the revving video.

have at it folks, thanks in advance

Sounds like the crank bearings are shot. Get a long screw driver and place the tip against the top of the motor and the handle up to your ear......then do the same thing but this time place the screw driver on the lower part of the engine.....you will be able to tell where the knock is coming from......but in your case it sure sounds low....
I would not be reving it like that although the damage is probably done by now:unsure:

Mine made a lot of bottom end noise at idle, but not up in higher RPMs until I synced the carbs up. If you're not sure if they've been synced or not you may as well start there. Once I got mine synced (only bench synced because I don't have a manometer yet) the knock at idle went away.

i figured synching it would help because it doesn't make that noise at higher RPM's. I'm actually gonna tear it down and do a rebuild until i get a new helmet and some other attire.

Mine makes the same noise when it's not firing on all four cyclinders. I also noticed that you have no air filter at all. I cann't even get mine to start without a filter of some sort. Mabe that could help.

Well i fixed her, took 2 days, chem tool, seafoam, bb's and alot of shaking. I knocked all the rust of the tank cleaned the petcock and carbs (with minor adjusting) and now she runs like a champ. No knocking idle or anything. Ran her around a bit and she's still a hoot to flog. Can't wait until my Gixxer swingarm comes in.

idle drop tune and sychronization will cure many mysterious knocks when the carbs are out of whack the whole engine is out it usually is the clutch basket slapping back and forth.

but sometimes the 3 starter clutch bolts coming loose will sound the same..

2 most common sources but further investigation is needed