FUMES 73 Plymouth Valiant

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fbard65

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Can't figure out why my 1973 Plymouth Valliant burns a half a tank of gas after traveling 60 miles and my inside smells like fumes. No one can figure out why.
HELP !!!!
 
Tough for us to figure out too! Did it start all of a sudden. After a fuel pump change? We need more clues.
 
What engine, what carburetor, what transmission, what gears, how tall are the rear tires, and yeah, did this just start? Have you changed anything recently?

And if the inside of the car smells like fuel or exhaust, you have bad seals, plugs, or holes of some kind in the body. Which is probably a completely separate issue.
 
Pictures of everything, tank, lines, pump and carb. Give us a good idea of what we are working with and it’s general condition.
 
I took it to a mechanic shop for a tune up and it started every since 2 yrs ago. Went back again and they replaced the carburetor and the problem still exists and became even harder to start. So, went to another shop and they added I think an electric fuel.pump. I'm not good with parts.
 
fbard65 said:
I took it to a mechanic shop for a tune up and it started every since 2 yrs ago. Went back again and they replaced the carburetor and the problem still exists and became even harder to start. So, went to another shop and they added I think an electric fuel.pump. I'm not good with parts.
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What plugs did they put in? What year and engine? A electric pump could put out too much pressure and it's pushing past the needle and seat.
 
fbard65 said:
I took it to a mechanic shop for a tune up and it started every since 2 yrs ago. Went back again and they replaced the carburetor and the problem still exists and became even harder to start. So, went to another shop and they added I think an electric fuel.pump. I'm not good with parts.
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Without a lot more information, we’re all just going to be guessing.

I mean, is this a slant 6 we’re talking about? Or a stroked 440? Is it a factory gas tank or a 10 gallon fuel cell?

IMG_4301.jpeg
 
fbard65 said:
Slant 6. Factory gas tank
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Ok, now we’re getting somewhere. So you say you’re getting like ~7 mpg with a /6, making the wild *** assumption you mean half a tank by actual gallons (8 to 9) and not just by a possibly inaccurate fuel gauge.

And it smells like fuel in the cabin? Or just exhaust?

Is it an automatic transmission? Is it shifting properly? Stock carburetor? If you pull the dipstick does it smell like fuel?

I’m assuming the fuel level only drops when you’re actually driving? There’s no puddles or stains under the car right?
 
It has a new fuel gauge and I do not have any leaks. Smells like both to me, to be honest. I noticed that my tail pipe is full of black sutt. Yes automatic transmission
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Well a new fuel gauge doesn’t mean it’s accurate. Actually more likely the opposite, but whatever.

Tail pipe full of black soot would indicate its running really rich, which would explain the gas mileage and the smell.

You need to check the fuel pressure, carbs are only supposed to have about 7 to 9 psi at the top end. If you’ve got more than that it’s probably flooding, and that’s before we even address the likely remanufactured carb and its tune. Does the car sit a lot too?
 
If you're getting exhaust fumes in the car you could have a rust hole way in the back. Years ago I was doing some work on my 66 Belvedere and had the reverse lights pulled out and man, the fumes came in like crazy and more so with the driver's window down.
 
Well the quality of the remanufactured carburetors isn’t always the best, although I’m assuming that you’ve just got some remanufactured 2 barrel carb on there.

You’ll have to verify the fuel pressure before you even bother much with the carb. It’s also possible the float is set wrong, but it won’t mean a thing if you’re rocking 12 psi or something.
 
1...You cannot figure fuel mileage by watching the gauge, if that is what you are doing
2...You can not figure gas mileage by the odometer, either, on a car this old Get a used Garmin Nuvi and use it for a speedo/ odometer
3....Pull plugs and look at them. What color are they?
4....What size tires, and figure out your rear axle ratio. To do that jack up one tire with front safely blocked. Put transmission in neutral, brake released. Can you turn the tire? If so, watch the driveshaft, and count shaft turns while turning the tire TWO exact turns. Your ratio will be a direct result of the shaft count, IE 2.73 the shaft will rotate 2 3/4 turns with 2 turns of 1 tire

If the one tire will NOT turn (in neutral!! / and brake released!!) then jack up BOTH rear wheels and see if they turn together. If so, you have a limited slip rear axle. Now turn one tire ONE turn, exactly, while counting shaft turns.

SMELL IN CAR This can be DANGEROUS. Carbon monoxide. Do you have full tail pipes to the rear? Is there ANY rust holes in the body into the interior OR TRUNK?
 
Then there is tuneup / engine condition/ carburetor.

If you don't have one, wander over to MyMopar.com and download the 73 factory service manual. That one, and several others, GOT THERE from the efforts of guys on HERE

Has anyone evaluated the engine, AKA leak down test, compression? Where is the timing set, and has anyone verified that the vacuum advance and centrifugal advance is working properly?

I don't remember when Ma got away from adjustable valves on slant sixes, you need to investigate if the valves are adjustable, and SET them if they are so

Has the carburetor been "gone through" and cleaned, etc? ---and this gets back to watching the spark plugs color. If they want to run blackish, the carb is too rich

Also does the engine run up to proper temperature? An engine with no stat/ stat failed open may run COLD and not run properly
 
67Dart273 said:
1...You cannot figure fuel mileage by watching the gauge, if that is what you are doing
2...You can not figure gas mileage by the odometer, either, on a car this old Get a used Garmin Nuvi and use it for a speedo/ odometer
3....Pull plugs and look at them. What color are they?
4....What size tires, and figure out your rear axle ratio. To do that jack up one tire with front safely blocked. Put transmission in neutral, brake released. Can you turn the tire? If so, watch the driveshaft, and count shaft turns while turning the tire TWO exact turns. Your ratio will be a direct result of the shaft count, IE 2.73 the shaft will rotate 2 3/4 turns with 2 turns of 1 tire

If the one tire will NOT turn (in neutral!! / and brake released!!) then jack up BOTH rear wheels and see if they turn together. If so, you have a limited slip rear axle. Now turn one tire ONE turn, exactly, while counting shaft turns.

SMELL IN CAR This can be DANGEROUS. Carbon monoxide. Do you have full tail pipes to the rear? Is there ANY rust holes in the body into the interior OR TRUNK?
Click to expand...
I had full length tailpipe on my car and it still pulled in fumes with the reverse lights out of the trunk lid.... the back end of the car always pulls a draft and full length pipes helps but is never 100%.
 
Does the oil smell like gas? By chance, is s the neighbor kid siphoning it off during the week??
 
@fbard65, what part of Mississippi are you in?
There might be a FABO member close enough to you that would be able to put eyes on your Valiant and diagnose the issue.
 
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