Posted April 15, 201410 yr comment_445807 After searching, every carb tuning guide tells you how there should be no vacuum leaks in the system (1971' 240z). it also states to do with this the air cleaner assembly disconnected.Now I may be missing some very large step here… But with the aircleaner assembly off, aren't all your vacuum hoses disconnected (Meaning HUGE leak), minus the brake booster hose? Clearly i'm misunderstanding something.The reason I ask. I finally got my carb cleaned out, and now idles at a high(With air cleaner assembly off), but smooth 1100-1200 RPM. I then start researching how to reduce the idle, and came across people with brake booster issues causing a bad idle etc. I believe I have booster issues as well, and I am just trying to correlate all my issues before I go and start tinkering more. Edited April 15, 201410 yr by HuD 91gt Link to comment https://www.classiczcars.com/forums/topic/49030-quick-carb-tuning-question/ Share on other sites More sharing options...
April 15, 201410 yr comment_445810 I think you can plug the brake booster line off for your tuning purposes and then hook it back up before you drive it again. If it idles well but when you step on brake it drops down, your booster or hose going to it is most likely leaking. Link to comment https://www.classiczcars.com/forums/topic/49030-quick-carb-tuning-question/#findComment-445810 Share on other sites More sharing options...
April 15, 201410 yr comment_445811 The hoses into the back of the air filter aren't vacuum lines. They all vent fumes from the float bowls and the engine to be burned. Vacuum lines are usually found coming from the base of a carb or the intake manifold. Link to comment https://www.classiczcars.com/forums/topic/49030-quick-carb-tuning-question/#findComment-445811 Share on other sites More sharing options...
April 15, 201410 yr Author comment_445812 Ok, so blocking the booster line will simulate a working brake booster. I can understand that. I assume all the other hose attached to the air cleaner assembly (Float bowl vent, Air injection system, crankcase vents) don't matter? Thanks for the reply! EDIT: Thanks Mark. So the only real vacuum system is the brake booster. All makes much more sense. What would I do without this forum Edited April 15, 201410 yr by HuD 91gt Link to comment https://www.classiczcars.com/forums/topic/49030-quick-carb-tuning-question/#findComment-445812 Share on other sites More sharing options...
April 15, 201410 yr comment_445814 There is one more vac. line from the base of the front carb to the vac. diaphram on the dizzy. Link to comment https://www.classiczcars.com/forums/topic/49030-quick-carb-tuning-question/#findComment-445814 Share on other sites More sharing options...
April 15, 201410 yr comment_445818 There's a bunch of other vacuum activated stuff on the balance tube, all emissions-related. The "flying saucer" thing, the anti-backfire thing, and (I think) the "hat" thing, all use vacuum. If you remove all that stuff, the holes need to be plugged (BSPT thread). Those holes are handy if you want to hook up a vacuum gauge. Link to comment https://www.classiczcars.com/forums/topic/49030-quick-carb-tuning-question/#findComment-445818 Share on other sites More sharing options...
April 15, 201410 yr comment_445823 Basically all you need to do is make sure any air that SHOULD be going through the carburetor isn't going AROUND the carburetor. Any lines hooked up to the air cleaner are already upstream from the carbs and therefore irrelevant as far as tuneups are concerned. However, anything hooked up to the balance tube is downstream of the carbs so if there are cracks in those lines or other faults letting unmetered air get into the engine it'll lean you out and give you an erroneous tune-up.The brake booster doesn't need to be unhooked for tuneups if it's working properly (eg not leaking a bunch of air into the engine) Link to comment https://www.classiczcars.com/forums/topic/49030-quick-carb-tuning-question/#findComment-445823 Share on other sites More sharing options...
April 15, 201410 yr Author comment_445842 For some reason I thought the brake booster was vented to the valve cover, which really made me wonder why this leaking would do anything to the carb. It all makes much more sense now. So, I was right. I was clearly misunderstanding something. ha Link to comment https://www.classiczcars.com/forums/topic/49030-quick-carb-tuning-question/#findComment-445842 Share on other sites More sharing options...
April 16, 201410 yr comment_445873 My '73 has brake booster running to the balance tube, PCV running to the balance tube, and a valve cover breather line (not a vacuum device, per se) running to the air cleaner box (not a vacuum source as far as carbs are concerned, all upstream) Link to comment https://www.classiczcars.com/forums/topic/49030-quick-carb-tuning-question/#findComment-445873 Share on other sites More sharing options...
April 16, 201410 yr Author comment_445874 Where did you get your brake booster vacuum hose? Is it a cheaper alternative to the reproduction model at the theZstore? Link to comment https://www.classiczcars.com/forums/topic/49030-quick-carb-tuning-question/#findComment-445874 Share on other sites More sharing options...
April 16, 201410 yr comment_445876 On the car when I bought it. Link to comment https://www.classiczcars.com/forums/topic/49030-quick-carb-tuning-question/#findComment-445876 Share on other sites More sharing options...
April 16, 201410 yr comment_445877 So I'm not the only one who used a semi-automatic drill to modify an air cleaner. Link to comment https://www.classiczcars.com/forums/topic/49030-quick-carb-tuning-question/#findComment-445877 Share on other sites More sharing options...
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