Engine Knocking and Bogging

[DS]

I have a 2001 GS with about 11,000 miles. At start-up there is a knocking noise that seems to be at it's worse at about 2000 rpms. Sometimes the severity of the knock seems worse than other times, and there is always a drop in rpms associated with it. Once the bike warms up a bit it doesn't happen as much if at all. What worries me is that when the knocking is at it's worse I can feel it through my handle bars. If anyone has any incite on this GS issue it would be much appreciated.

[kman]

Is it a knock like metal on metal?  Is it just once or twice or is it a continuous knocking?  I will get what I presume to be a backfire sometimes when she is cold and at low rpm but I do not worry about that.  I guess what is get is more of a pop but I would say it is noticeable through the bars. If it is preignition then it can cause engine damage.  Usually preignition is a result of mods since the stock gs500 is set up to run on 87 so you really cant get fuel that is too low of a grade. 

[gregvhen]

listen good, if its mechanical it will have a rythum (most likely) with the RPMs. if it pre det/ spark knock, it will be some what sporatic and random.  the thing about spark knock though is that it is more likely when the engine is warm than cold, because the carbon inside ignites the fuel when its hot. try running a full tank of 93 oct. through it and see if it goes away. if it stops, then the cause is carbon build up.  have you done the 5* ignition advance? this could cause it too.  also if you do determine its pre det, then you need to clean the carbon out by running some seafoam (found at auto stores) through it to clean it up

[DS]

I appreciate the help on this issue. The knocking is random/sporatic in nature and only happens a few times before it becomes less severe or diminishes completely. It doesn't sound or feel like it is backfiring when the knocking happens. It sounds like a metal on metal sort of clank. The bike is stock and I have been running it on 93 oct. What is the 5* ignition advance? Thanks again.

[kman]

carbon buildup can come from riding too softly too.  if you give a few good runs on an entrance ramp or something like that it may help burn away the carbon.  No promises on that one though.  The bike is meant to run on regular so the 93 is probably not helping anything, especially since you are still having this problem with it.  93 tends to have a higher ethanol content depending on how out of control your local government is.  Ethanol requires more fuel than real gas to reach the right mixture so running ethanol would make your mixture lean, another source of knock.

[scratch]

Sounds more like the normal cam end clearance knocking. 

When was the last valve adjustment?

If it's LOUD, and coming from the bottom end, then I would suspect something more serious, but I don't want to put thoughts into your head if that's not it.

[DS]

I don't like to beat it up, but I do give the GS a good ride every so often to keep it healthy. I'm going to start burning 87 octane to see if that has any effect on it. I haven't checked valve clearance since I bought the bike in April. I need to do that. Could not enough valve clearance cause the knock and rpm drop? I will let you all know if I figure anything out. Thanks again for all the suggestions.

[dcb0ys09]

I just bought my 2001 gs500 and was about to post a similar question. But this one about nails my problem as well, here is what I noticed.

When I start the bike up with choke when its cold I don't get a knock. After the idle kicks up to about 3000-4000rpms i drop the choke to about half where it wants to idle @ 1500. From there the bike tries to stay at 1500. If it goes lower or higher i hear this quick knock and the rpms continue to try and stay at 1500. Once the bike warms up for a few minutes or to where I can take the choke all the way off and it sits at 1500 there is no more knock ever. Its only on warm up and when I am about half choke. The knock is random, its not continuous, its like something Kicks in for a sec then it goes back to doing its warm up. Any idea why? Rode the bike 100miles at a time and theres no problem. Idles fine once warm after riding for awhile. Just Half Choke and when its cold.