Gas fumes and empty gas filter. - '68 300

mgm1986

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Looking for some help to troubleshoot a potential issue. 1968 Chrysler 300 440 with mechanical pump, clear plastic fuel filter. New tank and sending unit. Edelbrock 1406 Carb.

When the car is started cold, the fuel filter fills up 80-90% with fuel and the car fires up almost immediately.

When the car is warm it doesn't start as easily and occasionally I smell gas while driving but have not been able to pinpoint when or what causes this.

What I did notice, after the car is warmed up and sitting at idle, the fuel filter is almost empty and only the occasional squirt of fuel is coming into the filter.

My biggest concern is the smell of gas since the car runs great but I have a suspicion these things may all be related.

Any suggestions on what might be causing this? I have some ideas but would like to know what others think before I start down the rabbit hole. Thanks for your knowledge! :thumbsup:
 
I'm not exactly sure why, BUT how much visible fuel might be in the "clear" fuel filter is NOT a real good indicator of fuel going to the carburetor. Reason? When our '66 Newport 383 2bbl Town Sedan was newer, I felt it was better to have a fuel filter that was "clear" so I could see what was going on. This made sense to me, rather than the shiny metal filter that Chrylser used OEM.

BUT, what I noticed over the decades I drove the car (we still have it) is that in some situations, the filter would appear empty, yet the car ran great and fuel was obviously getting to the carburetor, not vapor. So, do NOT use what you see in the fuel filter as a good guide of what's going through it to the carburetor. This was what I saw happening over 140K+ miles of use. I have no explanation as to how this all happened, I just know that it did. I suspect Chrysler Engineering did too, which was probably one of the two reasons they used the full-metal case fuel filters.

As to the starting issues after the engine is warm . . . ONE thing to do is to make sure the complete ignition system is as good as it can be. Spark plugs in good condition with a gap between .035"-.045". I personally like NGK V-Power plugs, or their fine-wire Iridiums, for getting the spark exposed to more air/fuel mixture and a better burn. Make sure the rest of the ignition system is in good condition too. Having the timing at OEM specs (CHRYSLER specs, not what some associate might recommend) is a good baseline to which to start with. More on this later.

If it runs good after it starts, things usually are pretty good. Use about 1/3 throttle when cranking the engine, as that seemed to always work best for me with multiple carburetors (2bbls, Holley 4bbls, etc.). This is also inline with what the Owners Manual for the '66 Newport suggested (1/3 to 1/2). That setting has worked well with the fuels of earlier times and the progression of fuels since then. At least here in TX, as there ae something like 15 different fuel blends/specification that Exxon-Mobil makes for the USA. Which means that "E10" might be a national level of ethanol, BUT that does not mean tha fuels in TX are the same exact blend you get in your locale.

Learn what the CAR likes, not what you perceive it should like. This is one of my orientations such that "the equipment" and myself learn to get along together. Each car can have it's own personality differences, so learning them is important.

As to fuel smells, you need to determine if there are active leaks in the fuel lines/fuel pump/rank, but ALSO be aware that other factors can be at play here. Is the smell strong or just some evaporating vapors. The carburetor float bowl is open to the atmosphere, as the fuel tank is also vented to the atmosphere. Not a closed system as modern cars have.

How NEW are the fuel lines? Not just what you might see under the hood, but all the way to the tank. There is a short section where the fuel tank sending units meets the undercar line (with a special clamp that grounds the fuel tank gauge unit) and another small section at the rear of the stub frame, before the line gets to the rubber lines on either side of the fuel pump, and then the final section where the fuel pump is. IF there are any quesitons of their age, REPLACE THEM. Ethanol is a solvent and will degrade the rubber from the inside out, as the outer surface can still look decent, but can fail suddenly with possibly the outer layer of rubber falling off to reveal a seeping inner fabric reinforcement layer. As fuel evaporates, looking for these things before the fuel evaporates is important to finding them.

As to the carburetor, make sure the idle is set to "lean best mixture" and not too rich. I would also recommend a thick, OEM-style base gasket to keep the carburetor cooler. Edelbrock and Holley both sell them, as well as NAPA and other places. Might need to order them, though. About 3/8" thick, with plastic or metal bushings in each of the carb mounting stud holes, so only a certain amount of compression of the gasket happens. It might not be production correct, but it is just another effort to keep the carburetor cooler, as I have found out, too. There are versions which have 4 holes in them and some which have an open area under the carb. The 4-hole version might work better, but either one will work.

Ignition timing? Start with OEM specs and if there is no pinging on on-ramp part-throttle acceleration, you might try advancing the base timing 2 degrees or so. Then re-check WOT For pinging, too.

Understand, too, that fuel refineries are transitioning into "summer gas", which means the more volatile "winter gas" might still be in some stations' tanks. More volatile gas in higher-than-blended for ambient temperatures means it evaporates easier, which also means it can be more prone to percolation in a hot engine, when the engine stops and any fan air flow over the carb and engine stops. What's on top of the engine? The carb and air cleaner. So, fuel can get hotter in the float bowls and evaporate out, causing some "smells". Check for leaks first and then learn what might be normal in this respect.

Your carburetor might be new, but check the actual adjustment of the automatic electric choke. At an ambient 70 degrees F (ambient meaning EVERYTHING under the hood is at that temperature, not just the outside temperature), adjust the choke coil to just lightly close the choke plate. Check to see that the car starts and runs good there. That will mean the choke opens as soon as it can for best operation "as lean as it can". Then adjust the idle speed to 600-650rpm with the idle mixture screws adjusted for "lean best idle" using a tachometer only. Check the ignition point dwell if a points distributor is in the engine. No adjustment for an electronic system. Then set the base ignition timing. See how it all works, as a baseline, and then tweak from there to ensure things are as good as they can be.

Is the intake manifold stock cast iron or aftermarket aluminum? Just curious.

Sorry for the length, but I detected you might need some explanations on things.

Please keep us posted on your progress,
CBODY67
 
I'm not exactly sure why, BUT how much visible fuel might be in the "clear" fuel filter is NOT a real good indicator of fuel going to the carburetor. Reason? When our '66 Newport 383 2bbl Town Sedan was newer, I felt it was better to have a fuel filter that was "clear" so I could see what was going on. This made sense to me, rather than the shiny metal filter that Chrysler used OEM.

BUT, what I noticed over the decades I drove the car (we still have it) is that in some situations, the filter would appear empty, yet the car ran great and fuel was obviously getting to the carburetor, not vapor. So, do NOT use what you see in the fuel filter as a good guide of what's going through it to the carburetor. This was what I saw happening over 140K+ miles of use. I have no explanation as to how this all happened, I just know that it did. I suspect Chrysler Engineering did too, which was probably one of the two reasons they used the full-metal case fuel filters.

As to the starting issues after the engine is warm . . . ONE thing to do is to make sure the complete ignition system is as good as it can be. Spark plugs in good condition with a gap between .035"-.045". I personally like NGK V-Power plugs, or their fine-wire Iridiums, for getting the spark exposed to more air/fuel mixture and a better burn. Make sure the rest of the ignition system is in good condition too. Having the timing at OEM specs (CHRYSLER specs, not what some associate might recommend) is a good baseline to which to start with. More on this later.

If it runs good after it starts, things usually are pretty good. Use about 1/3 throttle when cranking the engine, as that seemed to always work best for me with multiple carburetors (2bbls, Holley 4bbls, etc.). This is also inline with what the Owners Manual for the '66 Newport suggested (1/3 to 1/2). That setting has worked well with the fuels of earlier times and the progression of fuels since then. At least here in TX, as there ae something like 15 different fuel blends/specification that Exxon-Mobil makes for the USA. Which means that "E10" might be a national level of ethanol, BUT that does not mean tha fuels in TX are the same exact blend you get in your locale.

Learn what the CAR likes, not what you perceive it should like. This is one of my orientations such that "the equipment" and myself learn to get along together. Each car can have it's own personality differences, so learning them is important.

As to fuel smells, you need to determine if there are active leaks in the fuel lines/fuel pump/rank, but ALSO be aware that other factors can be at play here. Is the smell strong or just some evaporating vapors. The carburetor float bowl is open to the atmosphere, as the fuel tank is also vented to the atmosphere. Not a closed system as modern cars have.

How NEW are the fuel lines? Not just what you might see under the hood, but all the way to the tank. There is a short section where the fuel tank sending units meets the undercar line (with a special clamp that grounds the fuel tank gauge unit) and another small section at the rear of the stub frame, before the line gets to the rubber lines on either side of the fuel pump, and then the final section where the fuel pump is. IF there are any questions of their age, REPLACE THEM. Ethanol is a solvent and will degrade the rubber from the inside out, as the outer surface can still look decent, but can fail suddenly with possibly the outer layer of rubber falling off to reveal a seeping inner fabric reinforcement layer. As fuel evaporates, looking for these things before the fuel evaporates is important to finding them.

As to the carburetor, make sure the idle is set to "lean best mixture" and not too rich. I would also recommend a thick, OEM-style base gasket to keep the carburetor cooler. Edelbrock and Holley both sell them, as well as NAPA and other places. Might need to order them, though. About 3/8" thick, with plastic or metal bushings in each of the carb mounting stud holes, so only a certain amount of compression of the gasket happens. It might not be production correct, but it is just another effort to keep the carburetor cooler, as I have found out, too. There are versions which have 4 holes in them and some which have an open area under the carb. The 4-hole version might work better, but either one will work.

Ignition timing? Start with OEM specs and if there is no pinging on on-ramp part-throttle acceleration, you might try advancing the base timing 2 degrees or so. Then re-check WOT For pinging, too.

Understand, too, that fuel refineries are transitioning into "summer gas", which means the more volatile "winter gas" might still be in some stations' tanks. More volatile gas in higher-than-blended for ambient temperatures means it evaporates easier, which also means it can be more prone to percolation in a hot engine, when the engine stops and any fan air flow over the carb and engine stops. What's on top of the engine? The carb and air cleaner. So, fuel can get hotter in the float bowls and evaporate out, causing some "smells". Check for leaks first and then learn what might be normal in this respect.

Your carburetor might be new, but check the actual adjustment of the automatic electric choke. At an ambient 70 degrees F (ambient meaning EVERYTHING under the hood is at that temperature, not just the outside temperature), adjust the choke coil to just lightly close the choke plate. Check to see that the car starts and runs good there. That will mean the choke opens as soon as it can for best operation "as lean as it can". Then adjust the idle speed to 600-650rpm with the idle mixture screws adjusted for "lean best idle" using a tachometer only. Check the ignition point dwell if a points distributor is in the engine. No adjustment for an electronic system. Then set the base ignition timing. See how it all works, as a baseline, and then tweak from there to ensure things are as good as they can be.

Is the intake manifold stock cast iron or aftermarket aluminum? Just curious.

Sorry for the length, but I detected you might need some explanations on things.

Please keep us posted on your progress,
CBODY67

Great advice above. Sometimes, the filter material in the plastic fuel filters and separate and cause a restriction or blockage. Fuel lines can deteriorate from the inside out. If you are replacing them, use fuel injection rated hose as it stands up better and longer with today's lousy fuel. Check really close for fuel leaks around the carb and try a phenolic spacer under the carb to try to help with hard hot starts. Good luck.
 
@CBODY67 Thank you for taking your time to write such a thorough and detailed response, this is great information to have!

To your question, it has an Edelbrock Performer Aluminum intake and the gasket definitely needs to be replaced as it is leaking oil onto the valley pan.

I will start by replacing all of the rubber fuel lines and see if that makes a difference before I start touching timing or making carb adjustments. I just hate the smell of unburnt fuel not knowing where it is coming from. Especially since I just installed a new tank.

I did install new plugs and wires and a GM HEI module (it had an electronic distributor) and gapped the plugs pretty wide. Last time I pulled them they were all burning clean so I don't suspect the ignition system is an issue.

To clarify my initial post, the car starts almost immediately when cold and when it's warm, it starts just short of immediately if I give it a little gas as the manual suggests. I don't consider this an issue unless it is related to the gas fumes I smell when driving.

For now I am going to assume the fuel pump and push rod are good since drivability isn't an issue.

I don't know when I will have time to get to it but I will post an update as soon as I have one.
 
Check really close for fuel leaks around the carb and try a phenolic spacer under the carb to try to help with hard hot starts. Good luck.

I will definitely heed this advice and see if I find any fuel leaks around the carb.
 
@CBODY67 Thank you for taking your time to write such a thorough and detailed response, this is great information to have!

To your question, it has an Edelbrock Performer Aluminum intake and the gasket definitely needs to be replaced as it is leaking oil onto the valley pan.

I will start by replacing all of the rubber fuel lines and see if that makes a difference before I start touching timing or making carb adjustments. I just hate the smell of unburnt fuel not knowing where it is coming from. Especially since I just installed a new tank.

I did install new plugs and wires and a GM HEI module (it had an electronic distributor) and gapped the plugs pretty wide. Last time I pulled them they were all burning clean so I don't suspect the ignition system is an issue.

To clarify my initial post, the car starts almost immediately when cold and when it's warm, it starts just short of immediately if I give it a little gas as the manual suggests. I don't consider this an issue unless it is related to the gas fumes I smell when driving.

For now I am going to assume the fuel pump and push rod are good since drivability isn't an issue.

I don't know when I will have time to get to it but I will post an update as soon as I have one.
It sounds to me that everything is running OK. These cars can be a little temperamental to start hot and you can blame that on the gas if you want to.

The smell of gas is likely a venting problem with the tank. Look at the FSM and look around at your tank vents. Do you have the correct gas cap and is the gasket OK?
 
The smell of gas is likely a venting problem with the tank. Look at the FSM and look around at your tank vents. Do you have the correct gas cap and is the gasket OK?

Great question @Big_John

I was wondering about the gas cap as it doesn't appear to be vented. When I take the cap off to fuel up it does release pressure. How would I know if it is the right cap?

I don't see fuel around the vents but I also don't know where the second vent tube is routed. One vent is short and shaped like an upside down U. The other one looks like it goes up into the body somewhere. Will get some pictures when I get back in the garage.

When I replaced the tank I did replace the short rubber lines that connect to the vent tubes but I don't know where the second vent tube is routed.
 
The vent I am curious about is the one with the red arrow in the attached. I reconnected this with new rubber line when I installed the new tank but I have no idea where it is routed.

1968 Chrysler Fuel System.png
 
Great question @Big_John

I was wondering about the gas cap as it doesn't appear to be vented. When I take the cap off to fuel up it does release pressure. How would I know if it is the right cap?

I don't see fuel around the vents but I also don't know where the second vent tube is routed. One vent is short and shaped like an upside down U. The other one looks like it goes up into the body somewhere. Will get some pictures when I get back in the garage.

When I replaced the tank I did replace the short rubber lines that connect to the vent tubes but I don't know where the second vent tube is routed.
The second tube goes into the frame rail. If you overfill the tank, gas will drip out of that tube and onto the ground, just in front of the left rear wheel.

I don't believe the cap is vented with your car.
 
@CBODY67 Thank you for taking your time to write such a thorough and detailed response, this is great information to have!

To your question, it has an Edelbrock Performer Aluminum intake and the gasket definitely needs to be replaced as it is leaking oil onto the valley pan.

I will start by replacing all of the rubber fuel lines and see if that makes a difference before I start touching timing or making carb adjustments. I just hate the smell of unburnt fuel not knowing where it is coming from. Especially since I just installed a new tank.

I did install new plugs and wires and a GM HEI module (it had an electronic distributor) and gapped the plugs pretty wide. Last time I pulled them they were all burning clean so I don't suspect the ignition system is an issue.

To clarify my initial post, the car starts almost immediately when cold and when it's warm, it starts just short of immediately if I give it a little gas as the manual suggests. I don't consider this an issue unless it is related to the gas fumes I smell when driving.

For now I am going to assume the fuel pump and push rod are good since drivability isn't an issue.

I don't know when I will have time to get to it but I will post an update as soon as I have one.
Thanks for the reply and additional information. The smell of unburnt fuel (as in exhaust system hydrocarbons) is a bit different from raw fuel (leaking from a fuel line or similar), which is a bit different from fuel vapors from the carb bowl vent after the engine sits and heats.

As to the oil leak mentioned, how is the pcv system working? Other than at the end rails, it could be that the valley pan is cracked to allow oil mist to escape, which can relate to the pcv system working.

Just some thoughts,
CBODY67
 
Seems like he fuel cap should be "Anti-Surge"? Which can be vented but have a valve which seals things so fuel does not escape under acceleration or driving up an incline, due to the placement of the filler cap.
 
I actually have no idea how the PCV is working, it doesn't look like there is much to it although I will investigate.

When I rev it up I see oil coming out around where the u-shaped outlet of the head on the passenger side above the exhaust crossover which appears to be blocked off. It seems this is likely where the oil is coming from that sits on top of the valley pan. When time permits I will pull the intake off to put a new gasket.

I did replace the last two pieces of rubber in the fuel line which were hard as rocks and definitely needed replacing.

After I have time to drive it again I will post an update if the fuel smell is better after replacing the fuel lines.
 
I suspect that if you probe the "U" area, it will be a dead end. If oil is coming out of there, something's cracked somewhere. Nothing that J-B Weld can't fix.
 
Good Afternoon
If you replace the carb mounting gasket with a thicker one, be sure to re-adjust the choke thermostat linkage to accommodate.
Omni
 
All new rubber fuel hoses from the tank to carb. A short test drive yesterday and I am still getting the occasional smell of fuel. Tried to pull the PCV out of the valve cover and although it broke in two where it went into the rubber line that connects to the carb, the valve was moving freely. Time to replace the valve either way as it was certainly brittle.

I confirmed when I rev it up hard I get a hint of blue smoke from where the exhaust crossover is (not oil), near those u-shaped holes in the head, on both sides.

After doing further research, although probably not related to the smell of fuel, I am going to need to pull the intake and inspect the valley pan to see if it is cracked. Getting a good amount of oil on top of the valley pan makes me think either a bad/blown pan gasket or a crack in the pan. Maybe I will get lucky and find this is the oil dripping on the ground and not from a leaking rear main seal (I suspect it is both).

Will post back when I have more info. Thanks again for all of your help and wisdom!
 
Took the intake off to investigate the oil on top of the valley pan. Considering how little I have driven the car, there was a good amount of oil on top of the valley pan.

I don't see any cracks in the oil pan although there was no gasket, very little gasket maker around the ports or near the end plates and every bolt holding the intake down had oil covering the threads. Aside from very minor scoring on the cam and some carbon build up on the exhaust crossover ports it looks clean which is a welcome relief.

I did notice however when I removed the carb that all four bolts had worked themselves loose. I am wondering if this might be related to the smell of fuel.

I am going to replace the valley pan and reinstall everything and will report back.

20240512_112704.jpg
20240512_113106.jpg
 
The loose carb nuts could have resulted in a rougher idle, but no fuel smells, typically.

Interesting how much oil was on the valley pan.
 
I am going to replace the valley pan
Some will disagree, but I'd replace it with a valley pan with a blocked crossover. I believe the Fel-Pro part # is 1215 (double check that). That may help with your hot starts.
 
There is also the possibility that the Intake gasket/ valley pan could have a small perforation/ hole in it. Here is an example what can happen.

DSC01049.JPG


DSC01050.JPG


DSC01052.JPG
 
Some will disagree, but I'd replace it with a valley pan with a blocked crossover. I believe the Fel-Pro part # is 1215 (double check that). That may help with your hot starts.
Good Afternoon
I installed one of the Fel-Pro valley pan with the blocked crossover on the 'Party Barge' for a couple of reasons. Hot restarts was one and it also saves scorching the paint of the intake manifold.
Word of caution, if you are using the original style choke thermostat (manifold mounted), then your choke will need to be re-calibrated. I replaced mine with an electric choke. Easy to install and you can calibrate it without having to remove it.
The 'down side' is that it is not stock looking.
The 383 starts fine and time that it takes to achieve curb idle is much faster.
Omni
 
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