Bad Exhaust Smell !!!

[skylineboulevard]

So I recently purchased a 1971 240z. It's in pretty good condition but I am in the process of restoring it completely. One issue I am having with the car is the very strong exhaust fumes. They are pretty bad and get into the cabin. Now I have read all the current threads so I know about making sure everything is sealed tight in the cabin. I just put on an the inner hatch seal and have the tail light gaskets on the way in the mail. The old ones are the originals and torn to pieces. All other hatch seals are already in place. The problem is not only the smell inside the cabin but outside as well.

I notice people driving behind me will switch lanes because of how bad the smell is. I went to a nearby Z shop to have the engine checked out. They tuned the carbs, replaced the clutch, and we are currently in the process of replacing the steering rack and outer tire rods to get the alignment 100%. They checked for an exhaust leak and said there was none and that the smell is normal but I have a hard time believing that the car came out from the factory with the exhaust so bad people changed lanes when they got

behind you. Will the exhaust just need to be replaced? The connector pipe is definitely rusted but apparently not leaking.

I know this is a somewhat common problem and it is really hampering my ability to enjoy my car. Any help is appreciated!

[siteunseen]

Are the plugs dark? Is your choke adjusted right? Sounds rich to me. Pull the plugs and put up a picture of them.

[moelk]

Mine smelled petrol both in and outside the car. I tuned the carbes couse i was runing rich and the smell was gone. Check plugs.

[Jarvo2]

A car with a carburetor will 'smell' a lot more than a fuel injected car with a catalytic converter just because the method of the air mixing with the fuel. I thought the same thing with my 72 and once the carbs were tuned properly it got a little better.

[Sean240Z]

Chris - Very nice 240Z and welcome to the forum!

Are you sure it's exhaust and not fuel vapors you are smelling? If it could be fuel you are smelling, check the fuel tank vent lines, especially the vent line that connects to the fuel tank to the top rear driver's side. Mine was so perished that with a full tank, fuel would spill out under acceleration and the fuel smell was really strong.

[FastWoman]

I see you're a mere 20 years old and lack the perspective that comes with age! And I would trade places with you in a heartbeat! (Great car, BTW -- all the better to own at age 20! )

Unless you hang out with old car enthusiasts, you wouldn't know how bad the tail end of an old car really smells. But I do. I remember being stuck in traffic in the passenger seat of an AMC Gremlin on the San Diego Freeway in the early 1970's -- without A/C. By the time we reached our destination, our eyes were bloodshot, and we could hardly breathe anymore.

California eventually led the nation in emissions control, and now the urban air in California is almost breathable. Modern car exhaust smells as fresh as springtime in the Rockies (well, not really), thanks to very precise fuel injection systems and catalytic converters.

Now, your 240Z, with old SU carbs and no catalytic converter, will always smell somewhat gassy if it's tuned right. If you were to tune (most of) the gassy smell out of it, it would sometimes be running lean, and that's not good for the engine. That's just how it is.

If you would like cleaner smelling exhaust, you might consider installing a good quality of catalytic converter. You can do that for a carbureted engine, so long as you don't tune it too rich.

If you want to entertain a project, you can also fuel inject the engine. The EFI of an L28 should bolt right up to your L24 engine. Superlen is currently developing an ECU for our engines that will make them run even better, with O2 sensor feedback, modern digital circuitry, and lots of great goodies. We're all very excited about it. This, with a catalytic converter on the tailpipe, should have your exhaust smelling like that of a modern car. You'll also enjoy greater responsiveness and much better fuel economy.

Edited March 19, 2014 by FastWoman

[grannyknot]

To add to what FastWoman says, some of us old farts will actually TRY and get behind you because we miss the glorious smell of raw gasoline and burning oil, wonderful. I have a 1970z and the smell was very bad when I got the car and after replacing hatch seal and door seals the thing that really did the trick was installing a BRE type rear spoiler.

It's well documented in the archives of this forum and many others that it usually makes a big difference as it breaks up the back draft that Kamm style rear end creates.

Welcome to the site, hope you enjoy it. Lots of good info here.

Chris

[skylineboulevard]

Thanks for the replies.

So I added some motor oil today and checked the spark plugs. They look fine to me. I accidentally deleted the last two pictures but they all look the same.

The carbs were just tuned so I don't think that is the issue.

As far as the choke needing adjustment that's a possibility. I will have to check it out tomorrow. The engine after being warmed up idles at exactly 1,000 rpm if that helps. This is actually the first car I've owned so I've learned a lot about the inner workings of these cars in the last couple months.

I will also check the fuel tank vent lines tomorrow to see what shape they're in.

I'll look into possibly installing a catalytic converter, EFI, and the Superlen ECU. I do plan on putting a Fairlady Z 432 style spoiler so if that helps then awesome.

I'll post back tomorrow after I look at the choke and fuel vent lines!

Edited March 20, 2014 by skylineboulevard

[Sean240Z]

Wrt the choke, make sure that when the choke lever is in the "off" position, that the nozzles on the undersides of the carburetors are fully returning (i.e all the way up). When I first owned my Z, I had an issue with one of my carbs where I'd push the choke fully fwd but the nozzle would not return to the fully up position (a combination of grime on the underside of the carb, an incorrect choke cable and a stiff fuel hose from the carb bowl to the nozzle).

[Jarvo2]

Here's my writeup, including a lot of useful pictures I've run across over the years from fellow members, of how to replace the vent tubes. Don't get too overwhelmed by the spiderweb of hoses, once you drop the tank it becomes easier to see how/where they all connect.

Dave's 1972 Datsun 240z: Smelly Situation

[Stanley]

Had a stinky exhaust, no stink now (the '81 head designed to lower emissions might be helping). Also advance timing as far as possible with little or no ping, clean and lube the chokes, fresh points (dwell per FSM), cap, condenser, and rotor, clean and gap plugs. Maybe new needles and nozzles for good atomization of the gas. Did all that stuff, probably helps.

If it's a smoker you might need rings, but it's a Datsun so probably not.

[ktm]

I think you may be exaggerating about cars changing lanes to get out from behind you. Once you are 5 feet away from the car the exhaust smell all but dissipates.

Tail light gaskets will cure your ailment inside the car. Also check the drain plug under the radio antenna (under the car), however, the tail light gaskets will be the primary leak source other than the inner hatch seal. When I got my car back from the painter I had to drive it without the rear inner hatch seal. I damn near passed out by the time I got home.

Check that your smog pump (air injection pump) is also working if you have a stock car. This basically injects air into the exhaust to help dilute the exhaust gas. It's most likely been removed however.

As FastWoman stated, a carburetored car will not run as "clean" as a fuel injected vehicle. If that is your goal, then you may consider converting to fuel injection which does help immensely.