pretty loud. I'm guessing the valve clearances are way out of spec.  but before I start that, is there anything else that could cause it?. bike doesn't run that great. just rebuilt carbs, changed plugs and oil. can a bad vacuum line of wrong air fuel mixture cause that? plugs were pretty black

depends on what you mean by "knocking".

There's a pretty ordinary noise the cams make by rolling side to side that is sort of a rhythmic "clunk" about once every second at idle.

"knocking" usually to me means a once-per-cycle bottom end noise.

Some folks use the word "knock" to mean "ping" or "predetonation" aka "spark knock" which can be caused on your bike by an extremely lean mixture but it won't ever do it at idle.

Anyway, in any case a noise like that is not related to your carbs.

sounds like ita coming from the head. it's definitely not a normal gs sound. have not checked clearances ever and it has 25k on it

also sound doesn't go away while riding or reving it gets better but I can still hear it. got mixture screws 3 turns out with a lunch box and cut down Yoshi.

mixture screws don't matter at anything except idle.

the lunchbox will require you to rejet, if you haven't already.

Usually bad valve clearances are the other way, they turn tight over time rather than loose. If you have a noise literally coming from the head then you need to pull the valve cover and examine everything. Could be cam chain tensioner or maybe you lost a valve shim or bent valve or a half dozen other things. Most of these things will have rather severe running consequences in addition to the noise like "loud tapping and no power"...

power is definitely down but it happened gradually. I did re jet it. and you think maybe valve guides or a burnt valve? really don't wanna take the head off

Quote from: drowningbird808 on October 18, 2017, 12:15:06 PM
power is definitely down but it happened gradually. I did re jet it. and you think maybe valve guides or a burnt valve? really don't wanna take the head off

IDK I'd have to hear it, ride it.

Do a compression test and settle your mind about the valves.

I didn't suggest pulling the head, I suggested pulling the valve cover and inspecting. That's a whole lot more practical. If one of the cam journals is loose, timing chain is flopping, etc., you can easily see it with the VC off. You can also check the valve clearances but for the valve clearance to increase the shim, top of valve, etc. would have to somehow grow. That doesn't happen. They wear the other way. Actually most of valve clearance changes is most likely due to the valve seat wear causing the valve to sit deeper in the head when closed reducing the lash at the top of the valve stem. You compensate by reducing the shim thickness to accommodate ordinary valve seat wear. So noisy valvetrain is almost guaranteed not to be due to excessive valve clearances unless you screwed up a valve adjustment.

If you had a burnt valve it probably wouldn't make noise. It would just have no compression and have very poor power. Especially wouldn't run when hot. Now, you might have carbon buildup on the valves causing them to not close fully which would eventually lead to a burned valve, but early on would cause a lot of valve noise and low compression. That is before the valves burn or bend (on mine, they bent). Compression test will give you some clue.

But I still don't know what you mean by "knock". Normally "knock" is a description of a bad rod bearing or crank main bearing. Normally valvetrain noise is not described as "knocking", but more like "tapping".  So "knock" may indicate bottom end.

Yes most top end problems cause 'rattling' 'tapping' noises, and typically 'knocking' sounds are bottom end problems.
Very common cause of this sort of noise could be the starter clutch.

Also bottom end noises tend to go away when you open throttle especially under load, they are louder when you close throttle. The only bottom end I have personally seen go on a GS started out as a clicking that the guy was complaining about. But a few miles later it was banging and hammering and dead.
Cool.
Buddha.

thanks. going to do some tests and stuff I'll update soon

Bottom end noise... could be the magneto rotor coming lose, the gear behind it gets a considerable amount of play. in having done so, it can make a pretty funky sounding noise. Dunno how to explain it, if you've drained your oil already however and don't mind replacing the gasket, it's an easy enough check.

Loose rotor is not common but a loose starter clutch which is bolted to the backside of the rotor is.  I had a loose starter clutch knocking and had the covers off both sides looking for the problem.  After buttoning it up and test riding it a couple more times I took the left side cover off once more and it was then an obvious loose starter clutch.  By the way, I had the right cover off once and the left cover off twice and never replaced either gasket, a light coating of green Permatex on the old gasket and neither cover leaked and they had both been seeping a bit of oil before on my 100k mile 02 GS.