Sorry this won’t help as I’ve never experienced or heard of anything quite like this but just for clarification purposes does this happen as your letting the clutch out or when you blip the throttle in neutral? How frequently does it happen?

 

This is directly throttle related- it can happen even if I give it gas in neutral.
I'm a daily rider, and it seems to happen once every three days or so.
It seems to be somehow timing related- like if I give it gas at just the right (wrong?) time or it's at just the right part of the stroke, then I'll hear that loud metal smacking sound.
It only happens when I'm at a stop or leaving a stop. I'll hit the gas and *smack*.

 

1. Any other driveability issues hot/cold, no matter how unrelated?
2. Start/idle ok hot/cold?
3. Any work done to the bike.
4. Does it tend to do it engine hot/cold?

 

1. No other drivability issues... Headlight gets brighter when I hit the gas, but every bike I've ever had has done that. Occasionally it'll stall when I give it gas from a stop before I let the clutch out, but that's rare.
2. Idles fine, starting seems to be getting rougher these days- if it's the first start of the day or it's been sitting for a couple hours, it'll take about 3 tries- first couple of times it'll sputter and try, usually the 3rd time it'll fire up fine.
3. No major work done to the bike, just basic maintenance. I've owned the bike for about a year and put about 10k miles on it. Previous owner bought it new, only put a little over 4k miles on it, and let it sit in his driveway by the beach and rust. When I bought it I changed all fluids, and have kept up with regular maintenance. Only issue was a minor coolant leak from the hoses going into to head, I just had to tighten the clamps.
4. Does it both hot and cold, no relation to engine temp or environmental temp.

When it happens, it hard and loud- about as loud as a whip crack.

 

1. Is an eletrical problem. Brightening of lights with modern electronics is an indication of poor voltage control.
2. Poorly controled voltage will result in poor charging leading to hard starting.
3. If regulator is bad, the ignition system can be under powered resulting in weak spark and incomplete combustion.
The bang you're hearing could be backfire in the throttle body.

 

Id check the spark leads/boots for damage. and the coil. also have you checked the voltage while the bike is running?

 

Sounds very much like pinging due to carbon build to me. Pinging definitely sounds very metallic like someone whacking your engine with a wrench or cracking a whip. You could try filling up a tank with the next level up octane rating and see if that helps. If so, you could run some injector cleaner (my favorite is SeaFoam) through it to clean up the carbon. If that is the case, it may also help out with your hard starting and random stalling too with some clean injectors.

 

I've been meaning to replace the spark plugs anyway, so tomorrow I'll replace them, and inspect boots. I'll go through the service manual tonight and figure out how to check the coil and regulator., as well as check running voltage tomorrow.
I already use mid grade (89 octane) gas in it, but I suppose I could use 91. I run seafoam through it every few months.
Thanks for the responses thus far!

 

It does backfire quite often, especially on deceleration.

 

It's far too hot to tear into the bike today. However, it died on me 3 times in about a 1/4 mile, so I decided to try turning the idle up. Apparently it was set as low as possible, black plastic nut wasn't threaded in at all, just hanging loosely off the inner metal part. I'm not sure how to set the idle properly without a tach, just I just turned it up from a chugga-chugga to a healthier sounding p-p-p-p.
I doubt I'll have time to tear into it to check everyone's suggestions until next week, so we'll see how it runs until then.

 

Going around checking this and that usually ends up in failure with the potential of introducing another fault, and then the real tail chasing begins. Have to form a troubleshooting plan with required checks made.

1. Is it one single bang and then off you go?
2. Any aftermarket add-ons...pipes, fuel processor, light bar, etc?
3. Did this just start one day out of the blue?
4. Any recent work done?
5. Is idle set to Kawasaki specifications?
6. Can you make it do it when you want?

It is normal for some bikes to dim the headlight at idle. Not an indication of electrical failure.

It

 

1. One bang then off I go.
2. Led underbody kit that I never use- doesn't even work unless I disconnect and reconnect it's fuse. K&N air filter. Everything else is stock except for the mirrors.
3. Think it just started one day out of the blue, months ago.
4. No recent work done. Oil change 2500 miles ago, tire change maybe 1500 miles ago.
5. Idle was low, I turned it up today, not sure how to set it to specs without a tach.
6. I cannot recreate it at will.

 

I'll be interested to see how your ride is running after the valve adjustment. From car and bike experience, these oddities, including the backfires, seem valve related. Or perhaps there's a small gnome living in one of your cylinders...? Highly improbable, but you just never know these days.

 

How many miles on it?

 

Just under 15k

 

I would just wind the idle up until it sounds faster.maybe even faster than you want and give it a quick run around the block to see if the idle was set way too low.
If it seems to be gone then,I would back the idle down a little so it idles nicely.
Regards Jason

 

A quick update:
Since turning the idle up, it hasn't stalled or made that metal on metal noise once.
While I'm happy that the problem seems to be fixed, I'd still like to know what it was and if it caused any damage.

 

Perhaps the clank was the engine turning too slowly to get past TDC before the flame wall hit the piston occasionally.