The Stovebolt Site Forums The Shop Area General Truck Talk Gas smell - ideas?

My 1951 3100 seems to produce a pretty pronounced gas odor if the garage sits closed overnight or what not. It has a replacement Spectra tank in the stock location. I re-used the original cap. Can’t seem to locate any leaks.

Theories:
1) Replace the cap? Anyone got a part number?

2) Fuel leaking by the carb into the manifold after shutdown. It’s a Rochester B so anything is possible. That piece should be easy to check with a flashlight down the throat. But not sure what the fix might be.

And I don’t see how a few dribbles down the manifold would produce this magnitude of smell.

You may get a "whiff" slight smell if you go near the gas cap but the smell should not be strong.
You need a vented gas cap. Rather than guess, I replaced my cap.

I replaced my original tank with a Spectra Tank as well. I replaced or rebuilt everything from cap to carburetor.
The only gas smell for me is when the gas heats up, like on a hot day. The gas cap will vent a little bit.
It's worse after pumping at a gas station (underground tank) and then the truck warms up in the sun (gas expands in the tank).
I only fill about 3/4 tank so that it doesn't leak out onto the paint.

Did you replace the 3 hoses connecting to the tank? The old hoses are known sources of gas smell.

Rochester's are known leakers externally but can also leak internally as well (fuel bowl drains overnight).
Hard to start in the morning.
The best solution in this case is to replace with a Carter YF as long as you get the recommended model.

A small drip of gas can fill a room with gas smell. That pungent smell is on purpose to bring attention to a problem.
I put my truck up on jack stands and got underneath with a creeper and a flashlight.
Sometimes you can feel a small leak by wetness on your fingers.

How would the bowl drain overnight internally? I’m well aware of the Rochesters shortcomings but not that one.

I actually have a YF to rebuild and it’s on “the list” but pretty far down the list as the truck is running pretty well with the B for now.

Forgot to answer all your questions.

Everything is new from the tank to carb. Only thing things that aren’t: the metal filler neck, neck to cab grommet, and the cap. I took a whiff inside the cab this morning just to test that theory. Interior of cab smells bette than the garage.

if cab inside smell better than outside in garage my bet is something on the outside. or its venting. I cut filler neck overflow smaller hose on inside of cab. put in a T and a high loop above filler. Then down thru the floor and put a charcoal evap cannister under the truck. no more smell when it vents.

[quote=hcb3200]

Cool idea. I’d like to see a pic of that

I also added a charcoal canaster to the vent on my fuel tank under by '37. It made a difference. I dumped the charcoal in glass pickle jar then added a couple tubes in the lid. The vent from tank goes into the jar at the bottom of the jar. The . other line goes under the truck. All fuel vapors are absorbed by the charcoal.

This is a great subject. I was under the impression that the vent on gas tank was to allow air to vent out of the tank when you fill the tank.

I also thought the gas cap on our trucks vented in only one direction, in to allow air to replace the fuel as it is being pumped out by the fuel pump. In addition, it’s second function is to stop sloshing gas and fumes from escaping.

I would love for some of our experts to confirm my beliefs or to set me right!

Lets start with the easy stuff.
Big Tube on filler and small tube on filler.
Big Tube is for filling. Small tube has two rolls. Let air out when filling and number two drain overflow from big tube back into gas tank.
Notice there is a bit of rubber tubing separating the filler neck metal from tank. This serves two purposes.
Safety is number one.
The gas tank is grounded the filler neck is NOT. if you try to measure resistance between outside of your filler neck and gas cap and your truck cab it should read null no connection at all no circuit. You don't want the spark on a empty vapor filled gas tank by a static ground or a electrical circuit touching the filler neck. that makes for a really bad day.
Number two is cab will move around a little and flex. you don't want that flexing you pipes causing leaks or other issues with your tank.

GAS CAP is vented both ways.
When you pull fuel out to engine it will suck air in so you don't have a vacuum build up and cause engine to die or worse catastrophic failure of your tank imploding.
Gas Cap will hold some pressure but ones it reaches a certain point will vent out. This varies by model.


Modern cars/trucks with EVAP systems have a sealed gas cap.
They have a separate hose running from tank / fill to a charcoal canister. There is a separate hose from charcoal canister to your intake manifold vacuum with valve. There is also a valve on the ambient air hole on or piped to cannister.
When you first start your engine the computer commands a close of the ambient air valve this seals the whole fuel system. it then measures the pressures as the vacuum is pulled on system. if it detects a leak it notifies the computer that there is a leak and turns on the check engine light. if no leak it reopens the ambient air value and it stays open all the time even when parked to let air and in off the system as needed thru the charcoal filter. Good thing for environment etc. Straight venting bad etc.
while running the valve on intake manifold opens and closes to pull fresh air thru the charcoal thus purging fumes back to engine to be burned up. this make the cannister last a good long time. (living on dirt roads is a different issue as the the dust will get in charcoal cannister).

LS swap guys. (I have a LS in my 56) Turn off all this checking and extra plumbing. or do like i did and leave all the plumbing to keep the fumed vented gas going thru a charcoal filter. Just not doing all the leak checks.

My tank has a sealed cap, it's in the bed floor so it fits flush with the wood. All venting of the tank is through the charcoal, out when it heats up, in when using fuel, this keeps the charcoal purged.

Another place to check for fuel vapor is the intake manifold. Inline sixes tend to pool fuel at the ends of the manifolds where there is less heat. If the carburetor is running rich due to poor adjustments or wrong metering, this makes for a smelly engine as all the extra fuel evaporates out of the intake runners. A nonworking heat riser doesn't help either.

Once I installed a Air/fuel ratio gauge, I quickly figured out mine was running pretty rich. I leaned it out with a metering rod change and mixture adjustment, most if not all the smell went away. I used to have to let the truck set outside after any driving so it would air out, now its straight into the garage except on the hottest days.

Wish I had something more interesting to report. Found the source of the smell this morning...little seep in the flare connection inlet side of fuel pump. Not enough to produce a drip on the floor.

Then I made it worse trying to make it better. Think I’m about done with this new fangled copper nickel line. They put some sort of black fitting on them and I’ve had a devil of a time getting them to seal. This is not the first issue I’ve had.

So, basically the charcoal canister would absorb the venting vapors created by expanding gas (eg. when engine is shut off and it’s hot) and then purge itself when the truck was running.

Just so I am clear, if I was install the charcoal canister in my ‘52 3100, I would have to tee into my existing vent line, install a hose with a high loop over the fill tube that goes to a charcoal canister installed outside the cab and install a sealed cap to force the escaping vapors thru the canister.

Yes that is a option and what I did. Many basic cannisters available online at the auto sites. Summit, Jegs, Classic etc. Soon as I get my pics from my truck ill post exactly what you wrote in images. may be a day or two my son has the truck at college.

I find with flare fittings it's best to tighten, then back it off and slam it tight again...doing this 3 or 4 times usually takes care of it as each time it's done the nut tightens up a little more as it stretches everything together making a good seal...just "strong arming" it doesn't work for me.

Mike B

I am by no means an expert on flares, but I was a machinist in a large heavy equipment manufacturer factory and learned a few things about leaky o-ring grooves that should apply to flares as well. Any scratch in a circular pattern will likely still seal but a vertical scratch (from inside the line to outer edge), or hairline crack in the case of a stretched metal flare, will leak no matter how hard you torque it.

I recently replaced brake lines and fuel lines using Cu-Ni tubing and have the cheaper style of flaring tool (Imperial, which is the best of these types) instead of the higher priced hydraulic kits. My initial flares were failing at a rate of 50%. I found that while I did the initial flare, that if the cone wasn’t perfectly centered over the tube, the flare would be a bit heavy on one side which would fail. My mistake was assuming the cone would center itself, but it didn’t center the part that goes around the anvil (tube clamp). Once the cone makes contact, recheck to make sure its perfectly centered will assure that you make good flares. Now I make nearly perfect flares every time!

Vital to centering is to be sure the ID is cleanly deburred also.

JW51 you asked for pictures so you shall receive. Here is my TEE and Cannister. Note i could have cut the pipes and made the TEE fit in line. The was not enough rubber in my opinion without cutting. since this was a running / driving truck with gas in the tank. I just removed the rubber link. move each small pipe left and right and did a around loop with tee at top. hose goes up into cavity in pillar so its not seen and then back down thru floor. High loop prevents full tank liquid gas from getting to cannister.
Cannister is just mounted to frame rail. I have a fuel injected LS up front and kept the matching cannister. you would only have the one hose in/out if just running a normal v8. the top is the ambient air inlet. In this pic it has no hose but there is a hose off it going to a vent with rollover valve and screen .

Thanks for the pics. I think I can follow up the point when you start taking about fresh air intake and the rollover valve? The rollover valve is in the fresh air hose?

Here is quick drawing of what mine is. I could not draw loops in the picture, so I marked where they are.

Yes rollover valve with screen is on fresh air hose going to inlet of charcoal canister.

This is rollover I used they are all over the online shops and parts https://www.tanksinc.com/index.cfm/...d=98/category_id=167/mode=prod/prd98.htm

Text from a Hemmings article.

"Ethanol gas is hygroscopic, which means it absorbs water more easily than gasoline. That leads to water condensation inside fuel tanks. Ethanol also erodes fiberglass tanks, rubber hoses and plastic fuel lines. It contributes to rust in fuel systems by creating condensation in the unfilled portion of gas tanks".

So if I understand correctly the system would be a sealed gas cap, a rollover vent, a charcoal canister and a vacuum port on the carburetor. Would this system also remove water vapor in the tank (as long as the engine is running) or make it worse?

I dread the day when the government outlaws non-ethanol gas.

Any air in the system will contain some water vapor, I don't believe you will get rid of it.
The Kansas City area has had ethanol in fuel so long I don't remember when it didn't. It doesn't seem to be hurting much on my truck and it will set for months with the same fuel in the tank. I bet right now it has fuel from last October or November, Quick-Trip 87 octane with 10% or more ethanol. Started right up last week and ran just fine. Maybe the sealed gas cap helps? The carburetors dry out pretty quickly, but they still have the same gaskets I started with four or five years ago.

Every modern car made in the last 20+ years uses this system so I thing you will be fine on water vapor. The more important thing on your rebuild especially if you have a old stock truck is those hoses. Modern gas eats them alive with ethanol They should be replaced with modern stuff.

This is an important subject to me so please permit me to blabber a bit.

As was said in the beginning of this post, the owner installed a Spectra tank. It is made (in Canada) to the original 50's Chevrolet material and specifications.
(I clipped this off the net) " Shelf life of ethanol-blended fuel is only 90-100 days since the blend was mixed".
Mixing or adding ethanol to 100% gasoline is done at the major US fuel terminals. From there it is distributed to various places and then taken to your local gas station.
**Hopefully** the gas station tanks feed from the bottom so a level of phase separated material is not just sitting at the bottom.
**Hopefully** the gas station sells enough gasoline to keep the fuel fresh or maybe someone keeps tabs on how long the ethanol sits in the stations tank.
Government legislators and the politicians and the environmentalists are not concerned that bad ethanol can destroy Jerry's (buoymaker) new gas tank.

If I had to use ethanol, I would not let it sit in my tank before I either use it up or drain it out.
The real problem for me comes when they pass the law that says I can no longer have non-ethanol gasoline.
I don't want to replace my tank so in trying to think ahead, I'm looking for options.

If you live near any boat yards (and/or boat storage areas), boat fuel needs to be ethanol free.

I used this website to find ethanol-free gasoline in northeastern NC.

Some small-engine sellers (like Toro) void their warranty on some of their equipment if you do not use ethanol-free gasoline.

I now use it in my Suburban and in all my small engines.

I’m with buoymaker. I’ve had my issues with ethanol and won’t run it in any of my seasonal gas powered equipment nor my ‘52 3100. Fortunately, I live in an area that sells regular non ethanol gas. It’s 30 cents higher but to me, well worth it.

I’ve got relatively easy access to ethanol free. It’s worth the extra money for anything that doesn’t run every day.

Ethanol free gas in this area is about $.50 extra a Gal.

Cheap?
Compared to the possible problems?

Unless you drive your stovebolt-engine/stovebolt carburetor regularly ?
- unless you empty/refill your gas tank regularly ?
- every month, maybe ?

My two trucks, snow blowers, lawn mowers, chainsaw, leaf blower all get it. My late model car gets ethanol.

It only became available here last year. I've started using it in my old stuff. Too early to tell if it's making a difference.

I get about 8 per cent better MPG with the non ethanol gas in my computer controlled modern cars which helps to make up for the higher price. It also helps with a weak idle condition in one of my cars when sitting at a long light in the hot sun. It's all I use for any small engine powered stuff. Exhaust smells better too.