How much exhaust and fuel smell is normal?

[Dino]

I'm so used to modern cars with cats that it's a bit hard to determine what is within normal limits on these old beasts.  At idle the TQ has a tiny amount of fuel smell coming out the back but I have to get real close to notice.  With the 1407 the smell is stronger although not nearly what it used to be so even though I tuned ignition by ear only, it seemed to have done wonders on many levels.  Yes I will still get the timing checked by a pro, not to worry.   

I 'think' that a bit of fuel and exhaust smell is normal, especially when I back it into the garage.  The smell is out of the garage within minutes.  Does this sound reasonable or should I find a better setting?

[68neverlate]

 

[68X426]

I 'think' that a bit of fuel and exhaust smell is normal, especially when I back it into the garage.  The smell is out of the garage within minutes.  Does this sound reasonable

Yes, normal.

Here's the definitive test: have the wife/gf hang around and do the smell test. If she hates it then you are dialed in correctly. 

Guys love the smell of fuel and exhaust and women hate it.

[firefighter3931]

Cam profiles with lots of overlap will smell dirtier at idle. Once the volumetric efficiency reaches it's peak the exhaust will clean up. Big cams send raw fuel out the exhaust...just a fact of life.

Dino, when you're adjusting your idle mixture use a vacuum guage and adjust the mixture screws for maximum vacuum. This will be your cleanest idle achievable given the engine combination. 

Oh, and make sure your ignition system is up to par....a weak spark will also cause unburnt fuel to exit your tailpipes and foul the plugs.


Ron

[Just 6T9 CHGR]

I 'think' that a bit of fuel and exhaust smell is normal, especially when I back it into the garage.  The smell is out of the garage within minutes.  Does this sound reasonable

Yes, normal.

Here's the definitive test: have the wife/gf hang around and do the smell test. If she hates it then you are dialed in correctly. 

Guys love the smell of fuel and exhaust and women hate it.

I concur! 

[cudaken]

 Dino, none if there is not a problem. My big butt has been hauled around in 68 to 70 Mopar for well over 300,000 miles. Only time I smelled anything was when there was a gas leak, exhaust leak or a body leak.

How old are your gas lines? My wife was smelling gas from her 79 Thunderbird (this was 30 years ago). My self and a friend looked and looked, saw nothing. Her complaining went on for months!  

Finally a few months later I took another look, the rubber fuel hose look a little damp, no fuel collecting on the intake? Changed the rubber line, bitching stopped!  

Last time I smelled exhaust was in my 69 Charger. Got the proper exhaust installed with tips (no longer dumping under the rear valances)  and installed the cardboard diver behind the rear seat and my eyes stopped burning.

Cuda Ken

[ws23rt]

This is a tough question. Like has been said the new cars are so clean we became accustom to almost no smell.
Those of us that drove these things all the time when they were new accepted what we smelled as normal.
I am wondering the same thing lately with an old and new car an the same time. When I pull the old one in the garage and close the doors (engine off) I can smell just a slight odor of gas but mostly from the ethanol. (It seems to be a stronger scent). The greater smell is from hot engine paint. My guess is that with carbs there will always be a bit of gas smell if nothing else because carbs are vented and the gas in them is hot.
The closed systems of the newer cars prevent that.
If the gas smell is strong and lasting there is a problem.
I am dipping back into my old memory's as best I can and don't recall much gas smell from my cars. I do recall smelling oil leaks more than gas leaks.

[Bob T]

Cam profiles with lots of overlap will smell dirtier at idle. Once the volumetric efficiency reaches it's peak the exhaust will clean up. Big cams send raw fuel out the exhaust...just a fact of life.

Dino, when you're adjusting your idle mixture use a vacuum guage and adjust the mixture screws for maximum vacuum. This will be your cleanest idle achievable given the engine combination. 


Ron

Ron, what would be a ballpark reading you would expect to see on the guage at idle? Have decided to go a get a guage to check mine. Similar raw fuel out and non stock cam on my 440. I need to confirm whether it's too rich down low.  Thanks.

[firefighter3931]

Bob, at idle if you can get the A/F ratio in the low to mid 14's it'll be pretty clean. The leaner the idle mixture, the harder it is to start.  

That being said : I have the 572 set up with 14.3 AFR at hot idle. I have to feather the throttle for a minute to keep it running and I don't have a choke.....just takes a bit of finesse.  

A single plane intake manifold with a large plenum also makes it more difficult as well.... until the manifold warms up and starts to atomize the fuel. Less of an issue with dual plane intakes due to the stronger vacuum signal pulling fuel from the boosters.


Ron

[Mebsuta]

Mine has smelled like gasoline, exhaust, and old vinyl for all the 25 years I have owned it, and the ones I was around before that were the same.  It doesn't matter; Carter or Holley, factory or aftermarket cam,  that's pretty much how it is. 

[flyinlow]

A single plane intake manifold with a large plenum also makes it more difficult as well.... until the manifold warms up and starts to atomize the fuel. Less of an issue with dual plane intakes due to the stronger vacuum signal pulling fuel from the boosters.


Ron

Yea tell me about it. Thermoquad on a Street dominator with no heat in January. I'm a feathering fool.

[flyinlow]

Probably   normal Dino.

Think about what comes out the tailpipe.

Nitrogen, Water vapor, Carbon Dioxide , and Carbon Monoxide you cannot smell. Even women can't smell these..

Un burnt / partially burnt hydrocarbons (gasoline) you can smell and irate your eyes and sinus.

Oxides of Nitrogen don't smell and you don't make much of that at idle anyway.


I think you said you had the Mopar 509 cam, you probably will smell fuel if you stand behind the car.

[71green go]

lol...I attended a "cruising on King street" in downtown Kitchener Ontario a week ago...really cool event where they shut down the down town main drive and vintage cars meet at a park then cruise to down town and park...100's of cars, 40's to 80's vintage mostly.....spectators line up along sidewalks to watch them all cruise in and finally park...and then look closer at the cars and talk to owners
I was blown away with the smell of fuel in the air lol, you can obviously see why fuel injection over carbs has to be a huge improvement!....I can only imagine the days when this was the norm.....I mean it was a strong fuel smell coming from the majority of cars...either they were not tuned correctly or that's just the way it is/was 

[ws23rt]

That is the way it was
Cars back in the day were not tuned correctly the same as today. But still at there best tune there was the aroma of hot cars in the air

[Ghoste]

Modern fuels boil off a lot easier too, I would think that could also be a factor.

[firefighter3931]

Modern fuels boil off a lot easier too, I would think that could also be a factor.

It's that freakin Ethanol crap.  This was never as big a problem as it is now when they were using the MTBE additive. Since that has been replaced with the corn piss we now have all these issues to contend with. 

As you probably gathered I'm not an Ethanol fan   

Corn is supposed to be served at the dinner table...not in your gas tank 



Ron

[Dino]

Thanks for all the responses.  It's good to know that some smell is normal.  I have the max amount of vacuum at idle right now, around 15.  When the timing is reset I will do this again to see if I can lean it out a bit more.  Besides dull the sound, are there any drawbacks to installing some universal cats?

[flyinlow]

  Besides dull the sound, are there any drawbacks to installing some universal cats?

Your turn... You try it first and let us know how it works.



I have thought about it.  You could run straight thru mufflers and it would still  not be that loud.  Getting enough flow and  getting the cat hot enough ,but not too hot would be  my concerns. Big overlap cams would give the cat a lot of un burnt fuel to process at lower speeds. I would hate to start a fire.

[ChargerST]

I wouldn't install cats. Thought about it as my car has a big cam and it wouldn't pass emissions (tweaked timing and carb and finally passed - but you couldn't drive with this setup ).
The problem is that unregulated cats don't do much and will stop working pretty soon after you install them - especially when used in conjunction with a big cam. Only regulated cats that alter the fuel/air ratio according to data received from one or two lambda sensor(s) will provide relevant gains and last.

[maxwellwedge]

Modern fuels boil off a lot easier too, I would think that could also be a factor.

It's that freakin Ethanol crap.  This was never as big a problem as it is now when they were using the MTBE additive. Since that has been replaced with the corn piss we now have all these issues to contend with. 

As you probably gathered I'm not an Ethanol fan   

Corn is supposed to be served at the dinner table...not in your gas tank 



Ron

Corn Piss....LOL!