1968 Strong gas smell after driving

[tomcwarren]

I've been bothered by this nagging problem for awhile now - my CS smells heavily of gasoline after driving (sometimes even while driving w/the windows down). Enough so that my wife worries when I park it in the garage - I've been leaving it outside for an hour or two, or leaving the garage door open to help dissipate the fumes, but I don't like doing that (car safety and Arizona heat).

Nothing obviously leaking from the tank all the way to the carb - no drips, no wetness that I can see or feel. Tank sender is tight/clean, lines look good (not cracked, etc), carb is newish Edelbrock, but I had the gas odor problem with the Holley I had on there before, too, so probably not a carb problem.

I have a 1/4" spacer between the manifold (Performer RPM) and the carb to try to insulate it a bit from the engine heat (351W, w/headers). All looks good from the fuel pump to the filters to the carb, too.

Is there a dye/additive I can add to gas that won't gum up the carb/plugs, kind of like refrigerant dye that'll help me spot any quick-to-evaporate leaks or carb percolation, etc.?

One other possibility is that the headers are leaking, and I'm running really rich, but that seems remote. It's hard to precisely pin down where the smell is strongest, but it appears to be mostly in the engine area, plus the fact that I can smell it as I drive (at times).

I don't want to go through the entire fuel system replacing things if I don't have to - hopefully someone has some insight into this. Has anyone had a similar problem w/a 60's stang?

Thanks,

Tom

 

[Midnight Special]

Is it only when hot? A leaky accelerator pump diaphram or float valve come to mind. Gas will perk out and evaporate before you can detect it Another problem I had years ago was a small leak in the line from the tank before it enters the engine bay and fuel pump...

 

[robert campbell]

Tom,
You are more than likely experiencing “percolation”. This occurs when a car gets hot and then when parked the heat from the engine transfers to everything. Especially to the carb. And it percolates “inside” the car not on the outside!

To verify this pull right in and quickly remove the air cleaner. Now go in the fridge and get a beer and a flashlight. Why do you have your flashlight in the fridge? Now bend over the fender and watch. More than likely you will see small drops of gas drip out of the atomizers in the venturi and land on the throttle plate. Can happen in both the primary and secondary of the carb. May need two beers.

Another question? Does the engine seem to roll a lot to start it first thing. A carb sometimes will drain its float bowls nearly dry. Then the engine needs to roll a bit unless you have a mechanical pump.

If any of this is happening, we need to correct it immediately. Steve (mechanical guy) and I will walk you through those steps and tricks.

Rob

 

[tomcwarren]

Thanks, Tim & Rob. I'll take a look at these 2 areas when I get a chance (have to move a couch down to my daughter in Tucson tomorrow).

The carb is new, so I'd like to think that it's internals are tight (pump diaphragm/float valve), but I'll check.

The hot/cold test is a good idea, too. I seem to remember that it didn't smell as much when I just ran it around the block and back, but I'll retest it from dead-cold (as cold as it gets in AZ in August) this weekend.

It always starts immediately (after setting the choke) cold, and if I don't touch the pedal when hot. I did have a cranky start last week after it had been sitting for a couple of weeks w/o a start, so the bowls probably were dry.

Note that it smells of gas as I drive, and immediately upon parking it - I'd expect percolation to happen _after_ engine shutoff, with some delay before enough gas escapes to make it strong enough to be noticeable, but I guess it could be percolating as I drive it.

I'd love to move up to EFI and eliminate the carb completely, but that's not in the budget right now.

Tom

 

[franklinair]

Rob-
Fuel odor while driving? Wouldn't any raw fuel be sucked into the venturi?

Neil

 

[gofastguy]

I will be watching this thread with interest. I just was thinking that ever since I got my CS my garage smells of gasoline, although not real badly. I may have to give mine the "two beer test" since I know that my Holley has a new front bowl assembly without the little percolator assembly and that it now has a Mopar accelerator diaphragm.

 

[robert campbell]

Rob-
Fuel odor while driving? Wouldn't any raw fuel be sucked into the venturi?

Neil

Neil,
Not while driving, but as soon as he parks it for the night. If he is also smelling a bit while driving it may be huge rich or the float levels very high.

Tom,
Internals being tight have little to do with it. Quarter inch spacer is very thin. Ford ran 1 inch spacers most of the time. What thermostat are you running? 180 or 195? Where you live, I might drop to a 160.

Rob

 

[murf104]

That very problem happened to me on a 66 many years ago and the fumes were coming from the "roller weld" that joins the bottom half of the gas tank to the top half. With the windows down the fumes were sucked from the trunk into the passenger area and a gasoline small was present. With the windows up the small was not so pronounced. Only fumes are at the top of the tank and no raw gas will leak at this welded seam, only fumes. A new tank fixed my smell problem. I located the problem by obsserving some small stains on the side of the gas tank but never did actually see any liquid escape. Maybe this will give you a clue to your problem, as it is very difficult to locate the source of an odor in a vehicle.

 

[aemoo28]

Rob, think back to my 68. She smelled up the whole garage more than one time with this fresh gas smell. When the distributor was switched out, the smell went away.

And there is no leak from the gas line to the carb? Or dist?

Wow I'm participating in a somewhat intellectual conversation about cars. Prob the beer and flashlight in my hand is helping. Good idea, Master Idle Rob.

 

[robert campbell]

Amy's car was running very hot until we straighten out her timing which finally involved a different distrubutor. A hot engine is more likely to percolate than a cooler engine.

The dripping will occurr inside carb on the throttle plates. You can see it and also put you nose as close as you can to the venturi's. The gas will smell very strong there. If this is occuring it can sometimes inject enough gasoline to "wash" down the cyclinder walls and cause premature wear on the piston bore and pistons. Needs to be addressed ASAP!

Living in "Arid-zona" is very hot!! If I had a Sunday driver it would more than likely have a 160 degree thermostat in it.

Rob

 

[rvrtrash]

I would check your fuel line from the tank to the carb very carefully. Look for stress cracks or signs of leakage in the hard lines. There is a piece of rubber hose that connects two parts of the hard line right at the front edge of the door, under the car, that a lot of people forget about. If that's old/brittle/cracked, you would probably smell gas from there, driving or not.

Steve

 

[robert campbell]

I know that hose and I better get busy on mine. She be old!!! Like me....

Rob

 

[CougarCJ]

If the fuel neck has not been suggested or checked, I would also look at the hose and or connections of the filler neck and tank in the trunk.

Coming in late as normal, want to make sure that we are talking solely about a gasoline smell, and not an exhaust smell.

 

[tomcwarren]

I'm tempted to just replace everything from the tank to the fuel pump, including the filler tube, gasket, hardline, rubber parts, etc. etc.

But the engineer in me says 'diagnose, then fix'. So I'll take everyone's excellent advice and check back-to-front, gasket/pipe/tank, hard-line, rubber bits, pump, carb, etc. as soon as I can get some time (#2 daughter is moving into the dorm @ ASU on Thursday, high is predicted to be 106+, so I'll be sweating off a few pounds ). I'll report back w/what I've found, probably this weekend.

Thanks, folks.

 

[Mustanglvr]

I drove my GT/CS about 20 miles with a bicycle in the trunk, with the lid tied down and I pulled over 3 times because of a strong gasoline smell. I never found what it was and I don't drive with the trunk open anymore, lol.

 

[franklinair]

How well does the gas cap seal??

Neil

 

[tomcwarren]

Looks pretty good, Neil. Rubber gasket is soft/pliable, regular anti-surge, twist-on cap.

At one point a few months ago I'd tried duct-taping the filler neck where it exits the body (in place of the gas cap) to see if fumes were coming out of it and causing my problem. No joy, still smelled gas. So a leaky gas cap is probably out.

Hope to do the entire fuel-system inspection this weekend.

Tom

 

[robert campbell]

Get her good and hot and drive her in the garage. Open the hood immediately and get the aircleaner off, or have it off already. Have your fender cover and flashlight at the ready. Bet you see dripping onto the throttle plates and a stong odor of gas coming up from the carb.

Rob

 

[robert campbell]

It was near 90 in Bremerton yesterday. Drove my car into the garage and was getting some stuff out of the trunk. Smelled a rather strong gas smell. Put my nose down by the pop open gas cap and it was quite strong. I would classify this as normal on a hot day. It seemed to dissipate quickly as the car cooled. Some smell of gas on a hot day would seem normal for pre-emission cars that later had canisters to capture the fumes from the gas tank.

Thoughts?

Rob

 

[harryz]

Strong Gas smell

Tom,

The folks who have mentioned fuel percolation as the root cause are probably correct. I also had this same problem with both Edelbrock and Holley carbs on my 289. I already had a 1" phenolic (plastic) spacer between the intake manifold and the carb. On my car, the fuel supply line to the carb comes up from the fuel pump on the left (driver's) side of the intake manifold. From there, I had a fuel filter and then a rubber hose that crossed over to the right (passenger's) side of the intake manifold and then to the fuel inlet on the carb. This rubber hose over the intake manifold seemed to be the source of the problem. When I changed the fuel inlet on the carb to the left (driver's) side of the car (eliminating about 2 ft. of rubber hose that can soak up heat) the problem disappeared. This was easily done on the Holley, but I don't know any way to do this on the Edelbrock.

I never thought to look at the throttle plates to see if fuel was dripping.

If you have an Edelbrock carb, then look at places like Summit or Jeg's for insulation that goes around your fuel lines to help prevent this problem.

Good luck,

Harry Z.