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Thread: Exhaust Leak and bogging out when pushing gas pedal

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    Default Exhaust Leak and bogging out when pushing gas pedal

    Hello all! I am new to the forum and new to my 1972 240z passed down to me by my father the original owner. It has a F54 block from 81-83 280z and a N42 head (75-76 280z) from what i gathered. My problem is that it has major exhaust leak. I can tell some hoses need replaced because they have some cracks and when i spray carb ether stuff on the hoses it changes the idle. But was told by my father that i have to replace manifold because it too leaks. I want to put on a header and new exhaust and am looking at zstore for there 6-1 header with MSA exhaust or the 3-2 header with exhaust. Wondering which one will sound better? Any suggestions would be great. Not looking for quiet, all for it sounding mean. Second part and more importantly, when i start it it starts fine and idles fine, however when i push on gas to drive or even rev it up it doesn't want to rev and acts like its gonna die. Can this be just because of the exhaust leak? Feels and acts like to much air getting in there. Drives, but i have to drive with choke half way open. Any input would be great. sorry for the long post, but need help bad and am in love with this car and want to get it running good so i can enjoy! Thanks in advance!

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    Quote Originally Posted by jryeager View Post
    F54 block from 81-83 280z and a N42 head (75-76 280z) from what i gathered.

    it has major exhaust leak.

    I can tell some hoses need replaced because they have some cracks and when i spray carb ether stuff on the hoses it changes the idle.

    Second part and more importantly, when i start it it starts fine and idles fine, however when i push on gas to drive or even rev it up it doesn't want to rev and acts like its gonna die. Feels and acts like to much air getting in there. Drives, but i have to drive with choke half way open.
    Does the engine have carbs or EFI? "Choke" implies carbs, so vacuum leaks are not as big of a problem. What kind of carbs? Could be that the carbs just need tuning.

    The biggest hose would probably be the one to the brake booster. That can leak also along with the hose that supplies it. The exhaust manifold would need replacing if it's cracked, but it might be fixable with just a resurface of the head-mating surface.

    Do you know where the exhaust leak is? It could be at the head or at the flange to the exhaust pipe.

    More details needed.
    1976 280Z, with some minor modifications

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    SU Carbs. My dad told me they should be good and he had them tuned not too long ago, but then again i dont think he has drove it more than ten or fifteen times in the last 4 years. mostly just parked in the garage. I thought about ordering the video from ztherapy to try and familiarize myself to it, but my mechanic neighbor is trying to sell me on weber carbs and im thinking about it because i know he can help me with them, but i was under the impression the SU carbs are learnable with the help of that video. Just got the car last week so havent got to much investigative work yet. Was told by my non mechanic father that the manifold needed to be replaced and was cracked and want to say it was the head. Not sure where the exact leak is and I am believing there is more than one. The hoses and the manifold.

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    My plan was to change out cracked old looking hoses and put on headers and see if that fixes the rough or at times non existing accelerating. The jumping when trying to drive putting it in first gear or the wanting to die when i rev it up, the non rev when i try and rev. it just misses all together. Gets better after warming it up for fifteen minutes in am. Drive to work and park for ten hours and then is really rough at night even after warming it up.

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    sounds like a mill saw when driving. real nasty lumber jack type noise as well if that helps any. mechanic neighbor heard it one time and told me i had a nasty exhaust leak. Sorry novice to it all and understand if I am not being clear or explaining enough for any real direction. appreciate the thoughts and any input though.

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    If you're sure the manifold is cracked then replacement is an easy decision. There are quite a few people who have said that headers weren't worth the effort. The stock exhaust manifolds are pretty good, and easier to seal. But if you're set on headers then maybe you'll be one of those people.

    A tune-up might be a good idea. Might help in the meantime, if you plan to drive it for a little while. But you're probably going to break some things when you replace the manifold. If you're positive that the manifold needs replacing, you might want to wait until you get things back together. Just in case you find damage that is worse than expected.

    Make sure that you know what type of head you have before you get headers or a replacement manifold. 75-76 is the square port exhaust, later is round. The code is cast in to the side of the head.
    1976 280Z, with some minor modifications

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