#3 cylinder not quite right

I've got my bike running pretty well, but the last couple rides I've noticed that the head pipe from the #3 cylinder isn't as hot as the others. The other three are so hot that I can only touch them for split second. The #3 pipe is still very hot, but I can still touch is for a good second or two. I checked the plug and it's leaner than the others, so I'm clearly getting spark. Could it be that the gap is too big and there's too much spark?

All four cylinders were running a little on the lean side, so I've been backing out the pilot screws trying to richen it up. Now the 1, 2 and 4 look plugs have a nice tan color to them, but the #3 is still white.

I assumed that the leaner it is, the hotter the pipes get, so I'm a little confused why the leanest cylinder would also have the coolest pipe.

You actually touch your exhaust headers to tell if they are hot or not? :ohmy:

Next time, try using a spray bottle with water, or a laser thermometer. :blink:

I'm not sure why you'd get the coolest pipe on the leanest cyl. Maybe someone else can figure that one out.

Yeah, I know I shouldn't, but I guess I'm too lazy to grab a spray bottle. I should clarify, though, that I definitely can't touch the #3 pipe for a second or two - more like .1 seconds compared to .05 seconds for the other pipes. It might not seem like much, but there's a definite, noticeable difference in temperature. I guess I'm being nit-picky here, but it just seemed weird that the leanest cylinder is also the coolest.

It may not be that lean, but perhaps you need a vacuum carb sync, becuase that cylinder is recieving a very small amount of fuel charge, or maybe misfiring not recieving any at all at idle.

GL.

A carb sync was going to be my next step, but I found a post in another forum that I think might be the answer — an exhaust leak. That would explain both why the plug was lean (more air flow) and why that pipe was cooler than the rest (exhaust escaping from the head rather than going the usual route). I just tightened the pipes, so we'll see if that does the trick.

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Sorry, it's an '80 kz750 (4)

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I actually checked those recently, but it's easy enough to check again. Thanks for the tip.

The experiences Ive had would tell me that the pilot jet or channel is partailly plugged. Replace that one or run a guitar string thru it & spray carb cleaner & air down thru the hole & make sure it comes out the carb body. With this crap gas they do that all the time if you let them set for 6 weeks without starting. Ive started running some fuel injection cleaner in the gas tank. Also make sure the air bleed holes in the front of the carb are clean too. Also once you have the plug fouled they will seldom clean out again with the crappy stock coils, replace it.