1980 Kz550 LTD cylinder 4 problem

First start of the season, went for a small ride, and then decided to do a carburetor sync. Carburetor 1,2,3, were all pulling vacuum and were easily adjusted.  Carburetor 4 was pulling almost no vacuum and no adjustment would change that. With the bike running I sprayed starter fluid around the intake and exhaust boots. RPM'S didn't change. So I don't think those were leaking by. Next I checked compression. Cylinder 3 and 4 were 150psi and 1 and 2 were about 145psi. Checked for spark. Had spark on all plugs. Swapped wires. No change. Swapped coils. No change. Swapped plugs. No change. No matter what I do the problem seems to stay with Cylinder 4. I'm not sure what to try next. Any suggestions would be great. 

Sounds like a plugged gauge.  If the compression is good the cylinder will pull vacuum even if the cylinder isn't firing, which you haven't mentioned.

So KZ550 cylinder 4 problem, should not be the tittle.     Vacuum Gauge #4 problem......... should be it.

Is the vaccum port on number 4 carburetor plugged?
Is the exhaust pipe on number 4 the same temp as the others?

I forgot to mention, I did swap the vacuum gauges. And the problem stayed with Cylinder 4. Hardly any vacuum on the #4 exhaust pipe and that cylinder is considerably cooler than cylinder 1,2,3 exhaust pipes. I guess I'll run through everything I did today again tomorrow. 

I should have said I swapped vacuum gauges. The problem stays with # 4 cylinder. 

I also should have said, changes on cylinder 4 sync screw made no change on the idol speed.

#4 cooler than the others? I'd check the idle circuit on that carb for plugged jets.

Vaccum for the petrol tap comes from no 4

Thanks Linuxrob. The vacuum for the petcock was the problem. This was my first time synchronizing  the carburetors and I didn't even think of that. I plugged the vacuum line for the petcock and was able to synchronize the carburetors with no problems. Cylinder 4 also now seems to be burning as hot as the others. Thanks again.