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Raw fuel smell after parking
https://www.slantsix.org/forum/viewtopic.php?t=58722		 Page 1 of 2
Author:  rich006 [ Fri Nov 20, 2015 6:05 pm ]
Post subject:  Raw fuel smell after parking
I've mentioned in a couple of other threads (here and here) that I have a strong smell of raw fuel after parking. It's so bad my wife is complaining about the smell in the kitchen even though the door to the garage has a pretty good seal. Now I understand on the older cars that might be normal, but on a '74 I have the charcoal canister which is supposed to capture those fumes.

At first I thought it was coming from the crankcase vent. I replaced the crankcase breather and the PCV valve. Then I decided maybe it was the fuel pump leaking gas into the oil, so I changed the fuel pump. That fixed it...for about a week or so. Weird. (In the mean time I adjusted the valve lash. While doing that, I went to adjust the idle and found the idle set screw was fully backed off, which surprised me because the idle had been around 720 rpm. After setting the valve lash, I set the idle to 750 rpm.)

At this point, still trying to fix the raw fuel smell, I noticed my PCV hose was cracked and brittle, so I replaced that. Then I noticed the air line from the carb to the charcoal canister was also cracked, so I fixed that too. But the smell is still there. I don't see any leaks in any fuel lines, and I don't smell fuel all the time, only after driving the car.

Tonight about 2 hours after parking, I took off the air cleaner. The fumes were strongest right in the carburetor. Is it normal to have a strong raw fuel smell in a carb 2 hours after parking?

As I mentioned in one of the other posts, the carb is new, installed right before I bought the car. I have the old carb, and I intend to rebuild it and install it eventually. Should I move that project higher on the priority list in hopes of fixing the smell? I don't want to be banished from parking in the garage this winter!

I'm learning as I go, so don't assume I know my way around a carburetor (I don't...yet).
Author:  Nicademas [ Fri Nov 20, 2015 6:29 pm ]
Post subject: 
Im by no means an expert but I was thinking you might be getting the smell from the main well bleed. This is a vent tube in the carb that allows air to premix with the fuel before it is released through the nozzle into the boost venturi. When you shut off the motor there is no more vacuum to draw fuel through the nozzle. So im guessing the excess fuel in the primary well tube is evaporating out the main well bleed.

Here is a picture of an edelbrock carb and how the fuel travels through it.

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Author:  SlantSixDan [ Fri Nov 20, 2015 11:12 pm ]
Post subject: 
See here, and carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download. Also make sure your heat riser valve is free and functional.
Author:  rich006 [ Sun Nov 29, 2015 6:07 pm ]
Post subject: 
Playing around this evening (the car has been parked for over 24 hours), I noticed that after I open the throttle by hand, fuel immediately starts leaking out from under the throttle body, actually from under the gasket to be more specific. If I continue pumping the "pedal" more fuel leaks out. There isn't any obvious looseness in the bolts holding the carburetor down to the manifold. I'll be digging into the manuals, but in the mean time if anyone has any ideas I'm all ears.
Author:  killnine [ Thu Feb 04, 2016 10:06 am ]
Post subject: 
Sounds like a vacuum leak, which would explain why it would idle so high with the set screw all out. The base of your carb is probably warped (if it's leaking out from the base). I had a similar issue and had to work through a couple gaskets and some gas resistant sealant, along with strongly tightening the bolts and grinding the bottom of the carb as flat as I could.
Author:  rich006 [ Mon Mar 07, 2016 3:44 pm ]
Post subject: 
I think I fixed the leaking flange gasket problem. I also found that a cracked vacuum hose was keeping the heat riser door in the air cleaner inlet from opening. Replacing the hose fixed that. And I uncapped the carb bowl vent and connected it to the vapor canister's bowl port, but after all that the smell persisted. Finally, I tried covering the air cleaner inlet with a rubber glove after parking. Bingo, no smell! Clearly the fumes are coming up through the air cleaner, which also explains why my air filter smells like someone dunked it in a bucket of gasoline. Any ideas?
Author:  neilskiw [ Mon Mar 07, 2016 4:20 pm ]
Post subject:  Lift The Hood...
Greetings,

when I park in the garage, I lift the hood. This allows manifold heat to rise, and the engine to cool more quickly. That way I'm not boiling the fuel out of the float bowl. Might be worth a try.
Author:  Reed [ Mon Mar 07, 2016 4:23 pm ]
Post subject: 
If you find the fuel is not boiling in the bowl of the carb you may have a filed carb body gasket or warped or cracked carb body.
Author:  rich006 [ Mon Mar 07, 2016 6:20 pm ]
Post subject: 
The engine always starts immediately if I follow the directions on the sun visor (when cold, press pedal to floor once then release; when warm, hold pedal partway down while starting). Doesn't that suggest fuel is remaining in the bowl while it's parked?
Author:  neilskiw [ Tue Mar 08, 2016 7:46 am ]
Post subject: 
Yes it does.

But if that hot manifold vaporizes even one tablespoon of fuel, your entire garage will be odoriferous. Just a suggestion..... you know..... happy wife = happy life.
Author:  rich006 [ Wed Mar 09, 2016 7:12 am ]
Post subject: 
Quote:
happy wife = happy life.
Amen to that. She's actually afraid I'm going to blow up the garage.
Quote:
when I park in the garage, I lift the hood
Tried that last night; no difference. Maybe tonight I'll try a bag of frozen peas on the carb. You know, some guys do the hyper-pak; me, I do the ice-pak. :-)
Quote:
If you find the fuel is not boiling in the bowl of the carb you may have a filed carb body gasket or warped or cracked carb body.
I'm not sure what you mean by filed carb body gasket, but given that covering the air inlet stops the smell, I think it's pretty clear the fumes are coming up through the air cleaner. Is it possible the excess fumes are because the engine is running rich? Or is it possible this is just normal?
Author:  SlantSixDan [ Wed Mar 09, 2016 9:13 am ]
Post subject: 
Shut off engine...no more radiator fan blowing air rearward. Heat rises. Carb heats up. Fuel in carb expands and/or simmers and/or boils (and fuel in pump-to-carb line expands into carb), escapes from float bowl into carb throat via the usual paths (nozzles), but since engine isn't running, that fuel isn't sucked in. It vapourises when it hits hot metal (throttle plate and/or manifold floor) then the fuel vapour permeates your garage via the air filter. To some degree this is a fact of life with carburetors—some California-spec carbureted Mopars of the '80s had air cleaners designed to close completely on engine shutdown—but yours sounds like an extreme case. Make sure you've got the best inlet needle/seat you can get on the carb (I like Daytona Parts Co's "DFV"), make sure the fuel level (float level) is right on spec or slightly lower, do the Fuel line mod if you haven't already, make sure the heat riser valve isn't stuck, make sure you've got a thick insulating gasket between the carb and the intake, add effective and sufficiently-large heat shielding between the carb and the intake, and the issue should decrease or go away.
Author:  Reed [ Wed Mar 09, 2016 9:16 am ]
Post subject: 
Sorry. That was a typo. I meant "failed" carb gasket. When I get typing fast my fat fingers miss keys or hit the wrong keys.
Author:  rich006 [ Tue Mar 29, 2016 5:35 pm ]
Post subject:  not as bad after very short trip
I discovered by accident yesterday that the fuel smell does not occur if I start cold, drive to the end of the street and back, and then park in the garage. This fact suggests that Dan is right about the heat being to blame. If the engine doesn't get hot, the fuel stays in place. I haven't had time to troubleshoot any further.
Author:  '67 Dart 270 [ Tue Mar 29, 2016 8:38 pm ]
Post subject:  gas boiling
I have this issue. As Dan pointed out, and fortunately and unfortunately, the slant six is configured so that the intake and the exhaust manifolds are "intertwined" and very close to each other. This is fortunate, at least because the intake is efficiently heated this way and the flow through the head is also efficient. This is unfortunate, at least because the exhaust manifolds are cast iron and are a large thermal mass. They are very hot during operation, and when shut down, with no air circulation, the heat rises up and heats the intake and carb pretty darn high. My Weber carbs are vented so, even with a substantial heat shield, I get gasoline smell from the gas boiling out of the carbs. I have an electric fuel pump, and a cut off switch, so I run the bowls down prior to shut off to minimize this (and the chances of wash down, gas going into the cylinders). I can imagine a lot of others do this as well.

I also made the error of having my Dutra Duals ceramic coated in BLACK - although attractive, the most emissive color possible. My exhaust manifolds radiate a ton of heat. I may actually have them recoated in silver to reduce this effect. See: http://www.raytek.com/Raytek/en-r0/IREd ... sivity.htm

That all said, I used to have a stock slant six in my '70 Valiant, and I don't recall ever having this issue with the stock carburetor. I miss my ever-reliable, but doggish, '70 Valiant. I sold it (ugh) to an old lady who wanted a reliable car....and a week or so later she wrecked it. Oh, regrets we have...

Brian
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