So I have been trying to get my jetting right after putting in a K&N drop-in without the restrictor.   At first I tried 127.5 and 1 washer, since it was close to the jetting matrix.  It responded ok, but I felt like I lost a little bit of top end power.  I went up to 130, and it still seemed to lack a bit of top end power.  I went up to 132.5 and seemed to get the top end power back, but now getting some surging in the mid-rpms.  I took out the washer, and I rode it tonight, but not enough to get a good feel for the response because I ran into a scary issue.

A couple times after the new filter and rejetting, I had experienced a "clack" type noise right before the bike started to take off at 7k rpm.  I caulked this up to the mixture being uneven in the mid and top range, and some kind of slack in the engine being taken up when the power hit.  Tonight after the bike warmed up a bit, I started to test the response again.  Right around 6k-7k rpm with the throttle almost fully open I got a scary rhythmic "clacking" along with a stall in the rise of the rpms.  I got off the throttle and rode the short distance home.  What in the world could cause this?  It only seems to have occurred at full throttle right around 6k-7k.  The bike hasn't lost top end power as far as I can tell.

I'm going to go back to the stock air filter and 125/40/1 washer because I know it was feeling good with that.  If the noise still persists, then I know it's not just a mixture issue.  I'm already concerned though, because I don't see how the mixture issue could cause the "clacking" noise.  I do experience valve ticking, and what I believe is the typical camshaft knock, but none of those have affect performance.   I'm really hoping that something is not seriously wrong, but I'm starting to worry...  What do you guys think?

7,600 miles on the bike.  Valve Clearances done at 6,300.

How are your plugs looking? If you're worried that you're running lean, that sound and symptom could be the sound of the mixture going lean to the point of detonation. If so, what you're hearing is detonation knock, which definitely isn't good in an engine that's known to spin rod bearings.

The right plug was light brown all over; it looked good.  The left plug however was a bit of surprise in that it didn't take any torque to break it loose.  It seems like it was loose in the threads...very odd as I'm sure I torqued it down.  Here is the picture of the left plug.  Looks a little bit different than the right in that you can see a light brown patch on the top of the threads next to the electrode.  I wonder if this is a symptom or a cause of the issue...



After doing more research, I think Ross might have be on to something.  I've learned a lean mixture is poor at resisting detonation.  Also, when detonation occurs, it puts pressure on your spark plugs, so it's possible that the plug was forced out due to the issue.  Also, you can see in the picture that the color strap on the electrode is closer to the threads than the tip of the electrode.  This indicates too much timing, which is also consistent with detonation.

I don't have time to look it up right now to verify, but I want to say I read somewhere, once upon a time, that 87 gas is more likely to detonate early versus a higher rated gas such as 89 or 92. I don't know how this bit of info will help or not in your situation, but it may be a short term solution to use a higher rated fuel till you find out the root cause.

The little I am able to connect among the dots... you have higher heat, or compression, or both on that side that would cause early detonation.  Most likely due to a lean condition as Ross mentioned..
But other thoughts include: maybe you got ahold of lower octane gas somehow...  I don't know if deposits can build up to create higher compression in these engines, but its another thought.

- Bboy

Thanks.  I appreciate any ideas.  I did test the compression over 1k miles ago, and it was actually a little low.  About 135-140 psi in both cylinders.  I think I'm going to go back to the stock air filter and jetting before I make any judgments about this being anything but a mixture issue.  I'm praying that the bike runs perfectly once I got back to that setup.

The spark plug backing out could have happened before the sound last night too.  I saw another thread where someone was experiencing pinging and knocking and then found that one of his plugs was loose.  He also mentioned the plug sparking closer down on the threads as opposed to in the gap, which would cause too much timing and possible detonation.

Correct, octane is a measure of resistance to detonation. Using a higher octane could band-aid the situation if the problem is detonation, but the source of the problem really should be looked into. Also, if the bike has the ignition advance mod, a higher octane fuel should be used.

It's possible the ignition has been advanced, as there have been many previous owners...  Is there a way to check and be sure of it either way?

That I actually don't know. I've read a little about the mod, but I have no idea how to identify it.

I can easily spot if this modification has been done to the plate.
http://gstwin.com/diy_timing_advance.htm

What I'm not sure about is how to spot if the rotor has been changed or modified.

EDIT:

Looking back at this thread: http://gstwins.com/gsboard/index.php?topic=59113.msg697089#msg697089

My color change strap on the electrode has been closer to the threads all along.  This would be consistent with an advanced timing I believe, but it's nowhere near conclusive.

So does anyone know how to spot a modified timing rotor?

It took about 50 mins to go back to the stock air filter, back to 1 washer under each needle, and 125 main jets.  I obviously torqued my spark plug back down as well.  It ran perfectly.  No hiccups of hesitation at any rpm or throttle position and definitely no clacking noise.

Moral of the story is that if you want to run the K&N drop-in without the restrictor, be prepared to do some serious tuning.  It might require a different needle jet as opposed to just adding washers.

I don't have the restrictor, so I'm not going to use the filter now.  If anyone is interested and trying it out, or has the restrictor already, let me know and I can sell it to you for $20 shipped.