Temperature of one exhaust pipe is much lower.

Temperature of one exhaust pipe is much lower at idle. Measured about 4" from head.
Any ideas? Thanks.
The cylinder works, RPM drops when spark plug wire removed.

Too rich on that cylinder or the others are too lean?

Have you adjusted the valves and vacuum synced the carbs lately?

There has to be more to the story that this. Why did you measure the exhaust temps? There must have been some running issue that prompted the check.

A little history helps a lot. New to you bike? You've owned the bike for years and this just cropped up? Bike been sitting for a while? Months? Years? Bad or rough idle? Pulling the spark plug on one cylinder is not really a good test like on an old car. These use wasted spark ignition and pulling one plug wire will shut of two cylinders most of time.

It could be caused by an irregular misfire, or if the carbs are not synched and set up properly that cylinder may not be contributing fully to running at idle. If your idle is for example 1000 rpm, this cylinder might only be getting the fuel to run at 500 rpm because of the slide position or something to do with the air screw or pilot circuit. As a result it will run cooler than the cylinders doing more work - it's a bit like riding a tandem bicycle and the person on the back isn't really pedaling, you'll get hot and sweaty and he'll be relatively cool.

car5car wrote: Temperature of one exhaust pipe is much lower at idle. Measured about 4" from head.
Any ideas? Thanks.
The cylinder works, RPM drops when spark plug wire removed.

Carb balancing issue.

Which cylinder is running cooler than the others? #2? Ed

Thanks for all responses!
I cleaned carbs and adjusted valves about 2 years ago and didn't ride it since because I had rattling generator. Finally I fixed generator problem and then had to rebuild petcock and replace carb bowl gaskets.
I have infra red thermometer and was checking head temp to prevent overheating, then checked exhaust pipes
I guess my 4th cylinder is dead because exhaust pipe temp is lower than head temp. Adjusting mix screw didn't change anything.
Right now I have bunch of problems:
bowl gaskets leak (ordered good ones)
timing chain rattles
4th cylinder is dead(?)
no gauges illumination lights
headlight died for a few minutes when I rode the bike at night
if 15V is too high, I have a regulator problem

I need a plan, solving worst problem first (cylinder)
1.Check compression of 4th cyl.
2. Check spark plugs (I installed new ones yesterday)
3.If spark plug is dry, I'll do carbs cleaning/adjusting/synchr.
I rode about 2 miles yesterday, so new spark plugs should show something.
4.Check timing marks.
5.Adjust timing chain

What did I forget?

If you cleaned you carbs two years ago, but ran them on the bike and let them sit it's quite possible that you could have a blocked or partially blocked idle system in that carb, it doesn't take much particularly if using the 10% ethanol fuel. If the cylinder is running when you open the throttle etc. the fault is almost certainly in the carb unless you have low compression on that cylinder.

That is interesting:
temperature of "dead" 4th cylinder is higher than 1st one! (measured next to spark plug)
OK, I'll check synchronizing before cleaning carbs.
BTW I cleaned petcock 2 years ago and it was clogged!

As Nessism suggested, do not forget to also check/adjust valve gaps.......don't ask me how I know......

I adjusted valves 2 years ago. Yesterday I checked synchronizing, and it was perfect. I also adjusted mix bolt turning it by 1/4 turn and watching RPM.
I rode about 10 miles yesterday, bike ran perfect except some farting around 3K RPM(backfiring of frontfiring(?))! Still low temp exhaust pipe!!!!!!!!
I have pod filters and 4 in one exhaust pipes, so cannot check which cylinder is frontfiring (exhaust). I tried to hold hand next to filters, didn't feel anything.
I'll check spark plugs tomorrow. Backfiring happens around 3000 RPM, so it has nothing to do with clogged idle jet.