Why does my 68 Fury 383 dump gas after shutting down? The smell is obvious and it’s done it ever since I owned it which is eight years now. I have an aftermarket 4 barrel carb. on it now for…. started out with the stock Carter two barrel, dumped gas with original and it’s still dumping gas now…any any ideas? This problem is driving me nuts would be a perfect car if it didn’t do this. It’s hard starting too after sitting a short while. Have 4 other Mopars…only this one does it.
Dumping gas
- Thread starter furyfever
- Start date
Fuel pressure? It should only be 4-5#.
The short answer? Most did it when new, even with the "real gas" we had back then. I know, Chryslers seemed to be the only corporation's cars that did that. Never did hear of it on Fords or GMs, back then. Just one of their quirks, it seems.
Under the intake manifold is what looks like a big ball of thick aluminum foil, except it has some yellow fiberglass insulation in it. The earlier suspicion was that it was there to insulate heat, but where it is, in reality, it blocks airflow under the intake manifold, which means that all accumulated heat from the intake manifold only has one way to go, up. Know what's in that path? The carburetor. Some have claimed that "insulator" was there to keep the valley pan gasket from cracking and leaking oil.
Some block the heat riser crossover, but in cold weather, it can make the engines more cold-natured, so best to leave it open and remove that "insulator" so heat can flow away from the bottom of the intake manifold easier. ALSO use the thicker OEM-style base gaskets, too.
In the mean time, you might lower the float level a notch or two. That might not cure it, but it might lessen the severity a bit. Also use about 1/3-1/2 throttle when starting, which can help clean things out quicker. Making sure the spark plugs are in good condition, too.
This is also the time of year when fuel blends transition from winter to spring. Winter gas is more volatile than gas for hotter times of the year. So if you get some winter gas and the temps get warmer, it's going to evaporate quicker out of the float bowls.
Just some thoughts and experiences,
CBODY67
Under the intake manifold is what looks like a big ball of thick aluminum foil, except it has some yellow fiberglass insulation in it. The earlier suspicion was that it was there to insulate heat, but where it is, in reality, it blocks airflow under the intake manifold, which means that all accumulated heat from the intake manifold only has one way to go, up. Know what's in that path? The carburetor. Some have claimed that "insulator" was there to keep the valley pan gasket from cracking and leaking oil.
Some block the heat riser crossover, but in cold weather, it can make the engines more cold-natured, so best to leave it open and remove that "insulator" so heat can flow away from the bottom of the intake manifold easier. ALSO use the thicker OEM-style base gaskets, too.
In the mean time, you might lower the float level a notch or two. That might not cure it, but it might lessen the severity a bit. Also use about 1/3-1/2 throttle when starting, which can help clean things out quicker. Making sure the spark plugs are in good condition, too.
This is also the time of year when fuel blends transition from winter to spring. Winter gas is more volatile than gas for hotter times of the year. So if you get some winter gas and the temps get warmer, it's going to evaporate quicker out of the float bowls.
Just some thoughts and experiences,
CBODY67
Sorry this is not normal even when new.
If it did it with 2 different carbs then as above check the fuel pressure. Next is check the float level, floats full of fuel, or needle and seat problem or the seat loose in the carb body.
If it did it with 2 different carbs then as above check the fuel pressure. Next is check the float level, floats full of fuel, or needle and seat problem or the seat loose in the carb body.
A friend of mine was having excessive pressure issues and replaced the mechanical pump as a fix. The pressure went from 7 to over 10 psi. A regulator fixed the problem.
No, it is not normal, but "fuel percolation" DID happen to us in the TX summers back then. Not "dumping" as such, but "percolation" which did cause a fuel smell and result in a longer crank time. Even when the car had about 7100 miles on it. We learned to live with it and use larger throttle openings to start it. With some finesse, it all worked.
Funny thing is that as allegedly rich as things might have been, no black cloud of exhaust resulted when the car started. In later years, I've come to suspect it might be more of an issue caused by weak sparks (for whatever reason) from the coil or condenser. Which is one reason I normally suggest that the ignition system be in top shape with spark plugs being frech and correctly gapped. Because, the way I see it, if there are fuel vapors in the intake manifold, they quickly evaporate when the pistons start moving, so sparks should ignite them easily. IF they could.
One side issue, to me, is that fuel does not "dump" into the throttle bores. As the ambient underhood air heats more when the hot engine stops, the first thing it can impact is the carburetor float bowl. Resulting in an expansion of the gasoline within. If it expands enough, it can be forced into the throttle bores from "percolation" activities. Probably not nearly as much as might be suspected, though. BUT, with the bowl vent valves from back then, if it expanded too much, it would come out of the bowl vent and run onto the intake manifold. Producing vapors all the while. Never did see that happen. So, to me, "dumping" is a gross exaggeration in terminology. BTAIM
CBODY67
Thanks for all great info. guys. I have a Holley 4 barrel on it now. As I said before it’s doing the same thing with this new carb. I looked up on YouTube how to lower the float level and I quickly did it this morning before I left the house. Seems better already. I don’t smell the raw gas as I did before. I’m still going to check fuel
pressure. I put a new stock fuel pump on it a few years ago. I’m sure it’s Chinese made so who knows what the pressure is. Thanks again guys. I’ll report back.
pressure. I put a new stock fuel pump on it a few years ago. I’m sure it’s Chinese made so who knows what the pressure is. Thanks again guys. I’ll report back.
With all of the underhood heat on these beasties....I kinda agree with CBody (hope that comes from Classic Beauty Body and not Pear body....but I digress). But, I added some heat shield tube for the fuel line from the pump....horrible ugly stuff, but will work. I did this to reduce chance of vapor lock. So, if the fuel vaporizes in the lines, no telling what is happening in the bowls. But, obviously if the heat also works on evap of bowl fuel, then opens the float valve, you will have a lot of fuel vapor under the hood. I think that both the carb insulator and for the fuel line could help.....cant hurt.
"Vapor lock" usually happens prior to the fuel pump, not after it in the pressurized sections of the fuel line. Chryslers were usually not prone to vapor locking nearly as much as similar GM cars were, by observation.
The carburetor bowl vents were only open at idle, for whatever reason. Those that had bowl vents may or may not have had bowl vent tubes inside of the air filter's area on the carburetor.
The carburetor bowl vents were only open at idle, for whatever reason. Those that had bowl vents may or may not have had bowl vent tubes inside of the air filter's area on the carburetor.
ynst
Member
"Know what's in that path? The carburetor. Some have claimed that "insulator" was there to keep the valley pan gasket from cracking and leaking oil."
The "bag" is a tappet noise suppressor. It has nothing to do with heating the carb. You won't find it on a 273, 318,36, will you but those manifolds get way hotter than a B or RB intake.
Check your fuel pressure or vapor separator.
From experience back in the day, on a hot day, with a hot engine, the problem called vapor lock would occur when you shut down for a while and then try to start back up.....and it aint goin easy. What I do not recall is whether you also had a lot of fuel smell. But, always interesting today with the old ones. I would also point out that this would not make me happy, as an under hood space filled with fuel vapor, then gets hit with all manner of electric sparking from motors, points, et al. A question for Fever on this....since this is a real problem, does the routing of the fuel line, both before and after the pump, come close to the hot exhaust.....we know that it normally runs near the front of the block up to the carb....but wonder whether the routing is that different in this case. And note that I think that heat from the manifolds is a major culprit on the line to the carb....just me.
When I was basically growing up with our '66 Newport 383 2bbl from the time it had 7100 miles on it, I wanted it to be as good as it could be. Our first summer with the car, I was attentive to all the car did and how it did it. Yes, I noticed some evidence of "fuel smells" from the underhood area. NO leaks or anything nearly that strong, just a bit of vapors. It did take a few more turns for it to start, but nothing nearly close to running the battery down, but it always started.
You could always install: tubing headers, aluminum cyl heads, and an aluminum intake manifold to more quickly dissipate heat, plus remove the "insulator" between the intake manifold and the valley pan for better air circulation under the intake manifold // an electric fan to run after the engine shuts down // the underhood items from a '72 C-body evaporative emissions system to collect and recycle any evaporative emissions // a carburetor with an externally-adjustable float
In reality, this is NOT the part of the year when "vapor lock" happens. Which means it is more fuel-related (changing blends from winter to summer) that can be more operative.
Enjoy!
CBODY67
You could always install: tubing headers, aluminum cyl heads, and an aluminum intake manifold to more quickly dissipate heat, plus remove the "insulator" between the intake manifold and the valley pan for better air circulation under the intake manifold // an electric fan to run after the engine shuts down // the underhood items from a '72 C-body evaporative emissions system to collect and recycle any evaporative emissions // a carburetor with an externally-adjustable float
In reality, this is NOT the part of the year when "vapor lock" happens. Which means it is more fuel-related (changing blends from winter to summer) that can be more operative.
Enjoy!
CBODY67
Your points do remind me that if I could, I would wrap the exhaust manifolds and some down pipe, I would. I did that on an MGA rebuild that had more tube headers, and it did not look horrible. But, would help underhood.
After shutting down motor…I can smell gas…for no apparent reason and after 5-10 min. wait, it’s very hard starting. Did this w/ original carb and new Holley 4 barrel.
A friend with big block fords forever, likes to raise the back of the hood with small block to increase airflow.....has done this for long time and it helps. But, with a known offender, maybe couple little things if weather very hot, first is let it idle for short stops, and second is to crack the hood up a bit while stopped with shutdown. Yes, ugly, but might help.
Fuel percolation is a common issue now days with the Puppy Pee gas we have. You can actually hear it boiling in the carb after you shut the engine off. Hard starting after a hot soak is also an issue. You may have too much fuel pressure and /or your float levels are too high. A thicker base gasket or carb insulator can help as well.
The "raise the rear of the hood" trick started with the 1967Mustangs. They didn't cool well at higher road speeds, so the raised rear seemed to help a bit in respect. Which is interesting as the base of the windshield is a high pressure area (used for cowl induction purposes) and should be putting air into the engine compartment from the rear. For convective cooling upon shutdown, it might help. I suspect it helped more with the FE Mustangs than the 289s. This was also before the ease of finding an aux electric pusher cooling fan was easy to do.
Simple solution would be to add an electric cooling fan(s), even deleting the mechanical fan, add a timer to run it after shutdown, upsize the charging system a bit, and perhaps a better solution results? Just a bit of modernization.
Enjoy!
CBODY67
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