mystery problem... might be lean in one cylinder?

[woliver]

I'm having a problem I can't seem to track down. It seems like a lean problem, but who knows! I have a 1985 VT500c

It's almost like I have a clog in my carb, but I don't think that's it. Basically, it's lacking in power until the midrange and the power comes as a surge. So if i'm riding, from a standstill, it will bog and seem to want to die until it hits about 3k rpms and then suddenly it will shoot off with tons of power. Usually the problem is gone in second and higher gears, sometimes it is ever-so-slightly there in second.

I also found that I can pretty much hold an engine speed anywhere except between 2.5 and 3.5k rpms. I can hold it steady at like 2.4 rpms, and then any slight movement will shoot it up to 3.5k, and then and movement the other way will drop it down to 2.4k again. There's also a slight popping on decel, which makes me think something is lean.

Here's what I've done so far: I've cleaned the carbs probably 10 times in the last week. Not only that, but I've done mechanics for like 15 years and probably cleaned hundreds of carbs. I've totally disassembled these guys basically down to pieces, cleaned everything, and the problem hasn't changed. I am *pretty sure* the carbs are clean. Of course, I don't pretend to be perfect or know everything so if the experts here say to clean the carb again that's what I'm going to do!

I also thought, maybe there's some trick to carb cleaning. Some bikes have little weird things that need to happen in order to totally clean the carbs, and most of them are pretty missable unless one knows exactly what they are. For example, I used to have an old honda moped, and unless you took out some plug called a welch plug, which I never would have seen if someone wouldn't have told me. Is there something like this going on here?

I also synched the carbs this afternoon, as per the sticky. no change. I changed the oil, thinking MAYBE i got bad oil or something and it was slipping the clutch just a tiny bit, enough so that I felt like low end power was lacking... but no change. I bought a new stock air filter, but no change. did the basics that I thought would never make any difference, like changing the plugs and inflated the tires and changed the the coolant. No change.

Everything seems good except for this low end issue. It seems to have a responsive throttle, I checked for airleaks (spray test), compression is good...

here's one more thing. I'm not sure if this is important. At idle, one of my exhaust streams seems much cooler than the other one coming out of the pipe. It's still kind of warm, so I know something is firing, but it's colder than the other one.
It also happens to be the one with further to go before it exits. Both headers are pretty hot, so I am thinking maybe it's just cooling on the way out... but there is definitely a temperature difference. Thought I'd mention it in case it's important, but I'm thinking it might not be!

Anything else I could or should check? My fuel flow is good, i've tried new gas, seafoam, i've even checked the fuses. I'm starting to want to check really weird things... i remember on two strokes you have to periodically clean the exhaust and clear out the carbon buildup... is this necessary on 4 strokes? this might be my next check, maybe there's a rat nest in there or something. But both pipes seem to have equal pressure...

Help! Please! thanks in advance!