VERY Disturbing Engine noise!

[Elmojo]

Hi all,
Sorry I haven't been around for so long. Mostly my Bandit has been running great, when I get to ride, which isn't nearly often enough. 
Anyway, some of you old-timers may remember a couple years ago I posted about a strange/scary noise my bike was making at idle and low rpms, especially when cold.

Here's my description from the old post:
As I was fiddling around, I noticed a sound that I had heard before, but was never able to track down.
My best attempt to describe this sound is somewhere between a *chunk* and a *spit*. I've been hearing this sound since I got el bandito about 2 yrs ago. I happens more when the engine is cold, but still some when it's warm. It only happens at idle or low rpms.
Try to picture two solid metal blocks, soaked in oil, whacking into each other at a semi-high velocity while encased inside a cast aluminum housing. Sounds kinda like upper-end engine parts smacking together, huh? That's what I thought too!
Needless to say, it sounds REALLY bad.
During my carb follies today, I was able to diagnose it a bit better.
I'm thinking it's some sort of backfire through the carb(s).
I had my hand on the carb when it did it, and the whole carb housing jumped a few mm whenever the sound happened.
I also had my hand once on the air filter with the cover off, and the filter bumped out towards the rear of the bike, like there was a bit of backpressure there.

I still can't pin down the metal-on-metal sound, but the spitting sounds like the aforementioned backfire through the carb.
Can anyone confirm that I'm not crazy and, more importantly, that my bike isn't about to frag like a grenade?!

Fast forward to today....
I finally got around to buying the gaskets and doing my valve adjustment.
That process went fairly well, except it took WAY longer than I'd hoped.
Anyway, so I get it all back together tonight and fire it up. First thing I notice is the very rough idle. I figure that's just because it's all been apart. I let it warm up a bit and it smooths out some.
I take it out for a gentle 'break-in' ride and everything seems to be okay. I notice that the engine is a bit more 'rattly" than before, but then again a few of the valves were a little on the tight side before the adjustment, so that wasn't totally unexpected.

Here's the big issue:
Before the adjustment, I only got the cough/spit/thunk noises described above when the bike was first started. After it warmed up, I'd rarely get the sounds again.
Now, it does it even more at idle and some after warm-up. If I put my hand on one of the carb boots, I can fell a fairly pronounced "pulse" every time it spits. If I'm standing close to the bike, I can feel it through the concrete floor!
Needless to say, I'm REALLY concerned. These are NOT good sounds to hear from an engine, particularly the thunk/clunk noise.
I recorded some audio tonight after the adjustment, but it just sounds like loud static.
I'll try to find something with a better mic than my cell phone to do the recording if you guys think it would help to hear it.

Any advice very much appreciated. I'm scared to ride until I get this resolved, and it's riding weather!

Elmojo
2002 Silver 1200S
Mechanically stock

[txbanditrydr]

I would suggest a carb sync - especially after a valve adjust.  Keep us posted.

[machu]

definately need to sync the carbs after valve adj.
As far as the tappet noise,mines sounds similar to yours,i was worried for abit aswell,but i think its just the nature of the beast.The bike runs like a champ otherwise.

[Elmojo]

Well, it looks like I'm back to square 1 now.
I tried the carb sync this morning, only to discover that I had apparently fudged the valve cover gasket, since now I have a nasty oil leak onto my headers! 
So now I have to tear it back down and try to salvage that pinched gasket or maybe put the old one back on. 
Anyway, once I get that sorted I'll post back with the continuation of the carb sync saga.
Elmojo

[Elmojo]

Okay, I got the valve cover off again. Somehow the gasket is torn/cut clean through in the front center next to the timing chain bulge. 
I'm not sure how that could happen, considering how much abuse I heaped on the old one getting it out, and it looks like new!
Anyway, I decided to try fixing this one rather than putting the old one back on, since I'd have to clean off all the gasket sealer again.
I'm waiting for it to semi-dry now, then I'll put it all back together and see what happens.

Back to the bad noise subject; do you guys really think all those terrible noises could be fixed with a simple carb sync?
I can believe the carb spitting, but that clunking noise sounds serious, and appears to be coming from lower down below the carbs, maybe midway down the engine.

Additional (semi-related info):
1) I did the TPS check last night and found that it was a bit out.
I adjusted it and it's balanced now, but I don't notice any difference, at least not at idle.
I won't be riding much until I get these other issues resolved.

2) I also decided this would be a good time to ditch the PAIR system, since it was seriously in my way for working around the valve cover.
I spent several hours fabricating stainless block-off plates and putting them on.
I did take some pictures of the whole process and would be happy to write it up as a tutorial if you guys are interested.

[Elmojo]

I have the bike back together and so far no leaks, so now back to the noise of doom topic...

After giving it a couple minutes at high idle to warm up, I tried the carb sync again.
At first, I thought the noises were gone; but once I got the revs back down under 2k, they started back, maybe worse than ever!
This is a continuation of the behavior I observed before. The missing and bad noises only seem to happen below 2k-ish rpms. Above that, it smooths out pretty well.
My main problem now (other than the noises of course) is that I can't get the revs to stabilize long enough to attempt the carb sync.
The spitting noise seems to be somewhat tied to the revs. What I mean is that sometimes when the carbs spit, the revs will either drop or breifly drop then jump up to high idle, around 2800.
My fiddling with the idle knob doesn't seem to affect it. The carb spitting, not the idle itself. Turning the screw does seem to raise or lower the idles as you'd expect, but it's running so erratic that it's hard to say exactly where the idles is set at the moment.
When I can get it to idles near the 1750 mark for more than a few seconds, I can turn the screw between carb 1 and 2 and see definite changes in the level of the fluid in the manometer.
Overall, the fluid level is fairly stable (not a lot of jumpiness) but it fluctuates from side to side depending on the revs, which are all over the place as stated above.
I'm really getting stumped here, anyone have any ideas?

I took a short video of the bike running, since my camera has a decent mic.
I posted it to my skydrive account here: http://cid-9d816cdbeb938785.skydrive.live.com/self.aspx/Bandit/Banditrunning.AVI?ccr=2329
EDIT: Much better video here: http://www.youtube.com/watch?v=jGYzxEdwUdI
You can really hear the spitting and see the carbs jump. Plus, you don't have to download it to watch!  

It's a little over 11MB, so it may take a bit to load if you have a slower connection.
Please take a listen and see what you think. In the video, both sounds (carb spit and engine thunk) sound the same, kinda like a tap or knock sound. In person, they are of course very different.
When you see me put my (greasy) hand on the carb boot, I'm feeling it pulse each time the carb spits.
I think it's only carbs 1 & 2 that are spitting, but I can't swear to that. I think the gas fumes are getting to me!
EDIT: I've confirmed that all 4 carbs are spitting, as you may be able to see/hear in the video. They alternate, in no particular order that I can see, but no 2 carbs ever seem to spit together.

Thanks in advance,
Elmojo

[Elmojo]

Well, in the absence of any replies here, I took my questions to another forum and got it sorted in record time.
For anyone who runs across this issue in the future, the problem is apparently well known and referred to as a "lean sneeze".
Basically, the bike is getting too much air for the amount of fuel delivered to the carbs.
The fix is either a jet kit (holeshot preferred) or trying the "ghetto jet kit", which consists of shimming the carbs with 1-2 .02" washers from Radio Shack under each needle.
Also recommended is pulling the carb bank, flipping the carbs upside down, drilling out the brass plugs that cover the air-fuel mixture screws, and resetting each one to 3-4 turns out.
Each carb will likely be set differently from the factory. Screw them all the way in until they lightly seat, then back them out 3-4 turns, depending on your bike setup and altitude.
Mine are currently at 3.25 turns out, but I haven't had a chance to ride-test it yet to see if they need more or less.
I'll pick up the shims today and report back with what I find.
The part number for the shims is 64-3022. This is a pack of 100 various washers. You'll need the #4 washers, which should mic out at .02" each. I'm told you'll have to sort through the pack (there are 20 of each) and find some that are the same thickness in order to get an accurate shim.
Cheers!

[stormi]

Hey Elmojo,

Thanks for posting back what the issue is!  A sneeze?  I had no idea that bikes could get colds!
Or maybe, given the time of year, it's allergies?

Wow, that's one diagnosis I'll have to remember.  I would never have guessed that they would do that if they ran lean. 
Of course, I don't think I've ever had a problem with a bike running lean.  Reaking (sp?) of raw fuel on the other hand,...   

[Red01]

My son brought his B12 over the other day, complaining it was running like crap.  I found the idle was set too low and all the carbs' clamps to the manifolds were loose.  It was "lean sneezing" too, not as bvad as yours, but it really stubled on quick accelerations.  There was also evidence of fuel mixture making it's way outside of a couple of the carbs.  Tightened the clamps and reset the idle and his bike was cured.

[machu]

So how is it running now?