Air Leak Questions

[Ruben911]

I have been fighting a hesitation on acceleration problem for the last two to three years. The only way to make it go away is to set the fuel/air mixture higher that 8% CO as measured with my Gunson tester at idle. If I set the CO at the recommended 3-4%, I get severe backfiring and hesitation. I have tried carb cleaner to detect the leak and have not had much success. Today, I tried a new approach recomended by an old mechanic friend of mine which involves using a flexible hose. Ypu put one end on your ear and then you place the other end on where you want to find leaks. I was astonished at how well this worked. I found that if I place the hose next to where the intake runners attach to the engine I can clearly hear air suction. This happened on all runners and was more severe in one in particular. All runners are well tightened.My questions are:

1) How long do the gaskets last and how hard are they to replace.
2) Is it normal to hear this air suction and if not, can this be sufficient to cause my hesitation under load. BTW, for comparison purposes, the suction at the injector o-rings is significantly lower than that at the intake runner gaskets.
3) Is there a way to test to make sure that this is in fact my problem without changing the gaskets.
4) Is the small hole next to the fuel distributor which is used to adjust the fuel/air mixture a source of air leak if left unplugged. My has not been plugged since I brought the car several years ago.

Thanks

Ruben
1976 911s 2.7L

[john walker's workshop]

there's air flowing thru the runners, so you may just be hearing that. usually, they don't leak at the head end. the boots that attach the runners to the airbox get very swollen and rubbery, so check there too. i use an oxy/acetylene torch to check for air leaks. you don't light it, you just turn on the oxygen and pass the tip around suspected leak areas. if the oxygen is sucked in, the idle speeds up. less messy than spraying carb cleaner all over the engine. the adjusting hole is not an air leak.

[Ruben911]

John, thanks for the quick reply. I forgot to mention that not only did I hear the air leak, I felt a slight suction breeze in my ear. I used a tygon tube that fit perfectly snug in my ear opening. Will leakage in these air intake runner/head joints cause the hesitation that I'm experiencing and if so what is the process for changing these gaskets (do I need to drop the engine to remove the runners). Thanks