Uneven cylinder temps. Need Insight

A few weeks ago I had issues getting my 84 gpz750 running and ended up finding the throttle partially open with the way the cable was hung up. Got great tips here from the forum. 

Since getting it running well, I’ve been focused on getting the rest of the odds and ends finished up. On Tuesday, I spent the day finishing up the tail light and turn signal wiring. At some point in the process I killed my battery, and got a new one Wednesday. I had been letting it run a minute or two every few days to keep things moving through the engine and carbs.

I had noticed the brand new header pipe on cylinder 2 was still chrome while 1 & 4 were straw colored and 3 is purple/blue at the first bend. 

When I fire the bike up now, it takes a bit longer to turn over and cylinder 2 header is cool to the touch after running a few minutes, while cylinder 3 pipe will be glowing red at the bend. The outside cylinders seem fine.

Before I start taking apart a finally assembled project, I wanted to ask for some guidance from the collective brain here. 

Bike hasn’t been ridden in 7 years but earlier this year I did a full tear down and clean of the carbs with ultrasonic cleaning. I have not vacuum synced the carbs either yet.

thanks for the help

Blue is hot, 
Brown/golden is correct
Metal colour is too rich or not firing. 
They look like delkevic single wall stainless down pipes. 
Question is why is 2 & 3 different. 
Likely blue is waaayyyyy too lean. 
Metal colour I doubt is not firing at all or if it is its waaayyyyy to rich. 
Remove the plugs and post electrode colour pictures. 

Yes, these are Delkevic pipes, with no miles on them only approx 10 minutes idle time.

Here are the spark plugs 1-2-3-4 from left to right. 

2 is the cold cylinder and 3 is the hot.

Difficult to say as those are presumably still choke rich mixture covered but No2 is def not firing. This'll give you an idea but it's not definitive for modern fuels.

Thanks for the graphic.

I tried swapping plug wires around to see if it followed the wire and it was no different. The bike has a rough idle on and off the choke, which makes the running lights and gauges dim and brighten as it goes on. It has a very hard time revving once warm and off the choke even. Think I'm going to be pulling the carbs off to take a look unless I am missing something.

The bike was running great one month ago. It also now sporadically spits fire out the pipe which I'm guessing is coming from #3 and am hoping isn't valve related...

I'm just guessing.
But if it spits fire I'm wondering if fueling is ok and the spark is sporadic.
Pull spark plug 2 after running for a bit.
Does spark plug 2 smell like gas or have fuel on it?

Measure each spark plug with an ohm meter to see if they are all similar.
Swap the plugs into different cylinders.
You could have a bad spark plug.

Do a compression test.

Thanks for the suggestions. I did a compression check at the end of August when I couldn't get it to run at all and got the following: 1 & 2 were at 120psi, 3 at 125psi, and 4 was 135psi.

I'll pull the plug out after letting it run a few minutes and check it out. Plugs are cheap enough I'll probably grab another set and throw them in and see what happens. 

One thing I just remembered, when I pulled #2 plug two days ago, the side electrode had collapsed onto the center electrode. 

84_GPz750 wrote:

One thing I just remembered, when I pulled #2 plug two days ago, the side electrode had collapsed onto the center electrode. 

As far as I know, that can only be mechanical damage caused by a foreign object or broken part. A broken valve will do that. Borescopes are pretty inexpensive these days.

TexasKZ wrote:

84_GPz750 wrote:

One thing I just remembered, when I pulled #2 plug two days ago, the side electrode had collapsed onto the center electrode. 

As far as I know, that can only be mechanical damage caused by a foreign object or broken part. A broken valve will do that. Borescopes are pretty inexpensive these days.

I would agree (unless you dropped a plug when they were out) if you are using the correct plugs that suggests something is "amiss" 

Wonderful... I sure hope mechanical damage to the engine or head is not the case but I will start down that path after checking the few suggestions I've received. This is quite the blow to my drive as I thought I was just about to throw my leg over it for the first time in years.

84_GPz750 wrote:

Wonderful... I sure hope mechanical damage to the engine or head is not the case but I will start down that path after checking the few suggestions I've received. This is quite the blow to my drive as I thought I was just about to throw my leg over it for the first time in years.

Before you dive in too deep I would suggest looking in the plug hole for signs of impact and fit a new plug. Where you have had the plugs in and out you may well have dropped one on the floor and don't remember (it's not a life changing event) which could have closed it up. Think positive   If it happens again then you know you have a problem

IF, and it's a big IF, there is any foreign object in that cylinder there is no evidence of impact witness marks on the plug earth strap. Additionally as he's run the engine already he's not going to damage it more by just trying again with a good plug.
I suspect that that plug either came out the box like that or it's been dropped. 
Although plugs "supposedly" come pre gapped they are seldom correct for the application we use them for so I always check/adjust the gap, new plug or not. Then you know where you started from. 
Re gap that plug, swop it for another cylinder, fire it up, see what happens and go from there.