MG Car Repair: 77 Midget Carb problems, vacuum leak, air leak

Question
Hey Howard,
My wife and I have slowly replaced part after part on our 77 Midget.  Our latest problem has come in the form of a very fussy carburetor.  
We replaced and set the float and finally got gas to stop leaking out of the bottom.  However, there now seems to be a vacuum leak that I cannot find.  The car idles just fine but when you advance the throttle there is about a second of lag time.  During that second there is a distinct air leak sound.  The sound continues as I give it more gas.  I don’t know if it is leaking air or gasping in for air.  I have tried to locate the leak by spraying starter fluid all over hoping for a jump in RPMs but it didn’t happen.  I am at a loss as to how an air leak could be so strong and yet so hard to find but with the fan running it makes it hard to feel any air leak.  
Also, we had the carburetor worked on once a few years back and the guy used a tool to adjust something.  I thought he put down where the Metering Needle went but I can’t be sure.  Is there any adjustment that needs to take place now… about 4 years later?  
Any ideas?  
Thanks
Chris and Christina in Chicago


Answer
The carb mixture adjustment is under the top cap down in the oil. The tool is a 3mm Allen wrench. Clockwise richens the mixture and counterclockwise leans out the mixture. If there was no oil in the top pot then that can be a cause of the hesitation as the oil is a shock to stop the piston from raising too quick and making a quick throttle opening lean. Most mechanics use a hose in one ear and search with the other end for hissing noises. You have to be careful not to put the hose all the way in your ear as you could damage an ear drum if you found a vacuum leak.
A method to determine if there is a vacuum leak set the idle low and slowly start to restrict the air going into the carb. If there is a vacuum leak you will arrive at a point when the RPM smoothes out and speeds up. If by restricting the air a little at a time you only slow the RPM down and finally cut the engine off, most likely there is no vacuum leak.