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smelly z


racer88

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I know there are many threads on the dreaded exhaust smells from our early z's. mine is a 74 with a warmed over 2.8 with round top carbs. i have done all the work on weather stripping sealants gaskets etc. I have read everything on the su's they are in great shape and I think tuned correctly. Having said that I still get the fumes in the cab when going slow or at a light. I understand the aero issues with the car. When i start it up at the local cruise night the people around smell the exhaust as well. My question is do the guy's with the fuel injected cars have the same exhaust smell or is it a carb issue. I am also looking for opinions on putting some sort of after market fuel injection and a high flow cat. if I cannot get rid of the smells I'm afraid i am going to give up on the z and sell. I have had many cars from the 60's and 70's and none have smelt this bad.

Thanks

Bob

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Sounds like you're running too rich and possibly have an exhaust leak. You may have a crack somewhere in the piping or a mating surface is warped. An easy, although not necessarily conclusive, test you can do is stick your hand down by the exhaust manifold (don't touch it!) and see if you can feel exhaust pulses. A leak will also be noisy depending on how much it's leaking.

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Hi Leon thanks for the response. my exhaust is a 6 into 1 header with a 2 1/2" mandrel bends in stainless that I tig welded together with a stainless magna flow muffler. did check for leaks and found none. My first thought was that I was to rich but if i lean it out anymore I get surging at a constent rpm. I have read many post on this site and classiczcar about the smells of our cars and was wondering if the fuel injection cars had that smell or was it only the carb cars

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Hi Leon thanks for the response. my exhaust is a 6 into 1 header with a 2 1/2" mandrel bends in stainless that I tig welded together with a stainless magna flow muffler. did check for leaks and found none. My first thought was that I was to rich but if i lean it out anymore I get surging at a constent rpm. I have read many post on this site and classiczcar about the smells of our cars and was wondering if the fuel injection cars had that smell or was it only the carb cars

 

If your round tops are worn around the throttle shafts, that will create a vacuum leak. This will cause to car to run lean at cruise unless you richen it up. Since the round-top SUs don't have a dedicated idle circuit, you will richen the mixture across the entire band.

 

Just another possibility.

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If your round tops are worn around the throttle shafts, that will create a vacuum leak. This will cause to car to run lean at cruise unless you richen it up. Since the round-top SUs don't have a dedicated idle circuit, you will richen the mixture across the entire band.

 

Just another possibility.

 

Flat tops do, but I read on the internet flat tops are smog carbs and are poor performers... /sarcasam warning/

 

Leon has it. Put a CO meter on there and dollars to donuts you are around 5 to 12% CO at idle....and that's why it stinks. I had a set of NOS (had, hell, I still have them!) 71 Round Tops off a car I bought-they had 6 months of drive time on them. I would put them on my cars when I'd smog test them. Never failed, and ran amazingly clean (ESPECIALLY with the AIR Functioning)... Chances are you have no AIR System on the car any more, so you are compounding your problem with the fumes.

 

I ran a 71 Z with an old 'smog legal' header which utilized AIR, it ran out the pipe exceedingly clean.

 

I also ran my 73 with ALL the AIR pumping into the #1 Header Pipe, and I was suprised to find that had a big impact on the tailpipe emissions as well, despite being injected 'in the wrong place'... I think just pumping the O2 into the exhaust is enough to burn up the residual HC's going out the pipe in back.

 

Try using a Toyota-Style Gulp-Valve to introduce O2 into the header collector and see if you drop the HC's. But you have to get the carbs working right first! Then you can scrub the exhaust.

Edited by Tony D
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Thanks everyone. I now have a plan of attack. I am going to gear up an O2 sensor to record excatly what is coming out the tail pipes and procced accordingly based on what I find. The carbs are in perfect shape as far as throttle shafts, pistons etc. The main jets are right on .100 thou and are perfectly round. The only issue I have is I do not know what needles are in my 4 screw carbs as they have no markings. I know holley and rochester carbs inside and out but the su's are frustrating me. I do suspect that it runs rich at idle and low speeds but turns lean at wide open throttle. If I acelerate at 3/4 throttle is pulls to 6500 and goes like a bat out of hell. If at some point in that run I open the throttle all the way it starts to miss. I have checked fuel pressure and it is steady at 4lb. any ideas

thanks again

Bob

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That definitely sounds like a rich condition. I would try leaning it out with mixture screws (1/4 turn or so) and see if a full throttle pull does any better. If it still misses lean it out another 1/4. Do it again until it doesn't miss with full throttle. Even if you had a color tune kit ( or the o2 sensor) you'd be at a better starting point than your at now. I think your just way too rich...

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It was my thoughts that the wide open throttle miss was that it was going lean as the throttle opened allowing more air in as I was already at about 4000 rpm when i crack the throttle wide open if I let off a little bit while it is missing the miss goes away and the car continues to pull hard. maybe I have to stop thinking how a holley would react. I shortened the mounts for the rear bumper and tucked it right up to the body and the exhaust tips are flush with the back of it.

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... I think just pumping the O2 into the exhaust is enough to burn up the residual HC's going out the pipe in back.

 

Tony, my question is out of ignorance so be gentle please. With the Z's Air injection is it really "burning" the residual HC up or is it simply diffusing them?

 

I was always under the impression that the Air injection systems were diffusion based to "appear" like the HC were less to meet US emissions standards.

 

If it is burning the HC, this is due to the proximity to where the air is injected and the associated heat from the exhaust correct?

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" If at some point in that run I open the throttle all the way it starts to miss. I have checked fuel pressure and it is steady at 4lb. any ideas"

 

ONE OF YOUR JETS IS STUCK DOWN PARTIALLY!

 

My 260 did the same thing, returned terrible fuel economy, and felt like an 'ignition cut' right at 5500. Lift the throttle incrementally (anything but WOT) and it seemed to pull to 7000. Drove me nuts looking for electrical issues. One day was under the carb and saw the jet stuck down on the rear carb. Repaired that condition, and my mileage went from 19 to 24, the car pulled stronger all around.

 

AIR does burn the HC's. Almost all the Emissions Devices of the day were centered around keeping the throttles open so enough O2 was in the exhaust to 'afterburn' as much HC as possible. If Toyotas with Dual Mikuinis could pass injecting air via gulp-valve with an idle setting of 3%CO, then so can our cars. AIR isn't in play at idle, but off-idle and really when you drop throttle it makes a big difference in the emissions out the tailpipe.

 

The issue in the exhaust manifold is that on drop-throttle it goes "Real Rich" with fuel as there isn't any air from the carburettors. AIR was a solution that allowed the carbs to stay closed to provide the fuel economy on coast. EFI used 'decel fuel cut' to perform similar action, TPS<X% and the injectors are cut off completely. It's one of the reasons the EFI cars seem to be so much cleaner. Guys "ripped all that emissions crap" off their carbs, then wonder why they get gassed on decel. No combusion happening and way rich HC on drop throttle and cruise-coast. Keep in mind cruise/coast also had big advance numbers because of the EGR and the more advanced you are, generally the more complete the combustion as it all has time to burn. Retard the timing and watch that exhaust manifold glow! It's still burning coming out the exhaust valve. The emissions engines were up on advance (with some retarded settings at given times) so by the time the exhaust valve opened there wasn't a lot of 'fire' left to continue combustion, but plenty of heat. Flash O2 in there in the form of fresh air, and POOF! The HC in the exhaust stream reignited and burned off.

 

You can see this on a five gas analysis. The key is the O2 percentage of the exhaust flow (Rayaap can probably give more detailed numbers.) I think you are normally around a balanced 8% O2, with CO2 in some ratio corresponding. If you 'dilute' the exhaust stream with over-injection, your O2 percentage goes way up. It was this cross check on the old BAR90 that triggered the 'dilution' fail and made everyone look for the obligatory 1/4" hole drilled in the headpipe to dilute the exhaust stream!

 

No, AIR was a combustion solution for excess HC, not a dilution solution.

 

Wow, I've inadvertently just coined a phrase for the current administrations plans for the money in my retirement accounts: "The Dilution Solution, we just print more!" :(

 

Where do I get a pig, on which I may rest my feet?

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It was my thoughts that the wide open throttle miss was that it was going lean as the throttle opened allowing more air in as I was already at about 4000 rpm when i crack the throttle wide open if I let off a little bit while it is missing the miss goes away and the car continues to pull hard. maybe I have to stop thinking how a holley would react. I shortened the mounts for the rear bumper and tucked it right up to the body and the exhaust tips are flush with the back of it.

When you floor the throttle the dashpot piston actually drops and the velocity of the air accross the bridge increases pulling an enriched fuel mixture into the engine until things equalize in the dashpot and intake manifold. You are definitely too rich! I'd bet money on it! Don't be afraid to experiment. You can't make it so lean you'll damage the engine. At least not a mostly stock engine.

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Yes, the original AIR was in the head almost. Tubes injected it almost at the back of the exhaust valve.

Some people cut them off and injected it in the manifold through tubes that did not protrude in the exhaust stream and picked up some incremental HP without emissions penalty, so moving them back 2" didn't make an appreciable effect.

 

Like I mentioned, I was shocked to find that the combustion seemed to still happen in an extractor (header) when I injected ALL the AIR Pumps output into the #1 primary tube, about halfway between head and collector. There must have been enough heat to start combustion and carry over to the rest of the cylinders when they all merged in the collector. I did not get 'dilution' issues, the balance of the gasses on the old BAR90 machine read correctly.

 

I had something else to say, but at 450AM, I've lost it in groggy haze...

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