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Carb 308 Reeks of Gas about 10 minutes after shutdown...

Discussion in 'Technical Q&A' started by Wayne 962, Dec 11, 2003.

  1. Wayne 962

    Wayne 962 Formula Junior

    Nov 27, 2003
    407
    I'm pretty sure I know the answer to this one, but the car reeks of gas about 10 minutes aftershut down. I figure it's the float bowls leaking down into the engine (and thus into the air cleaner).

    Unless I'm missing something else on these cars?

    -Wayne
     
  2. yelcab

    yelcab F1 Veteran
    Consultant

    Nov 29, 2001
    9,062
    San Carlos, CA
    Full Name:
    Mitchell Le
    Wayne,

    It could very well be the float bowls leaking etc .....
    But, in my case, and in many other people's cases with these older cars (20 years +), it is all the rubber fuel lines rotting out. The filler hose at the tank is the most trouble some one.

    When I rebuilt my engine, I also took the opportunity to replace every single hose of all kinds on the car. The fuel smell went away now, and has not come back. Even if I stuff my nose in the air intake and take a whiff, it is not that strong at all.

    Since you just got this car, I suggest you do the same and change all the fuel hoses. Then, you can worry about the carburetors bowls later.

    By the way Wayne, with all these free advice, does that mean I am getting a discount over at pelican parts? I need to spend beaucoup bucks on my 911SC this month.
     
  3. pma1010

    pma1010 F1 Rookie
    Silver Subscribed

    Jul 21, 2002
    2,556
    Chicago
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    Philip
    Wayne
    I don't think the bowls can leak quite as you describe. The fuel goes in the top and is metered by the main jet up through the emulsion tubes. People have reported on this forum that the plus in the bottom of the bowls can leak.

    Having said that - here's what I'd look for.
    1. Fuel hose connections to carbs. Pull the airbox off. Look at the connections when you run the pump. Leaks will be obvious. If necessary, replace the fiber washers. Get them from Ferrari.
    EVERYTHING else leaks in my experience.
    2. While you are there, look for leaks around the top gaskets/idle jet O-rings.
    3. Fuel hoses. I thought mine were OK when on the car, but pulling them off and rolling around in my fingers indicated otherwise. They all perish after 26 years or so. Bottom ones that connect the balance pipe are expensive. Use silicon or Ferrari/OEM. Don't use radiator hose (like some clown had done on mine). It will perish. The Ferrari stuff (about $10/inch!) has a special coating on the inside to make it oil/fuel resistant.
    4. Tanks. Run your hands over the bottom of the tanks. Mine left no deposit on the floor, but one felt "tacky". Pin point hole. Pull tank, flush, re-seal.
    HTH
    Philip
     
  4. WaltP

    WaltP Formula 3

    Nov 1, 2003
    1,457
    Cape Canaveral/Atlanta
    Full Name:
    Walt P
    For the balance pipe hoses, I used gas filler neck hose I got from a local parts house for .89 cents an inch. So far so good.
     
  5. yelcab

    yelcab F1 Veteran
    Consultant

    Nov 29, 2001
    9,062
    San Carlos, CA
    Full Name:
    Mitchell Le
    I called a local hose supplier asking for a couple of feet. They GAVE me 3 ft of this RED silicon hose impervious to gasoline for free. It seems they are used to dealing with corporate clients who buy 1000 feet spools so it was not worth the trouble for the paper work.

    Red silicon hoses matching the paint, free. Cheapest parts I ever bought for the car.
     
  6. 4Webers

    4Webers Formula Junior

    Nov 12, 2003
    276
    Texas
    Full Name:
    Darrell
    I would second that, unless you have a receipt within the last couple of years showing that they were all changed. Supposedly this is the #1 cause of engine fires in these cars.

    I would also check the accel pump gaskets, as I just found one of mine spraying my forward cam cover with fuel every time I stomped on the loud pedal. Carbs are coming off for new gaskets over Christmas...

    Even if everything is fine on your car - no leaking lines, no sticking float valves, etc - these cars can really pump out the gas fumes, just from having 4 big cans of gasoline sitting there open to the environment. As delivered from the factory, the later carb cars had a ridiculously elaborate Evaporative Emission Control System so they could meet US/CA standards. Not only is there a vacuum-operated flapper valve in the airbox inlet to seal the airbox from outside, there is a small electrical suction fan connected to the airbox that runs for a few minutes after shutdown to pull fumes into the charcoal canister. I would bet that none of these devices are still working, thus there is going to be some serious gas vapors emitted.
     
  7. Wayne 962

    Wayne 962 Formula Junior

    Nov 27, 2003
    407
    All good advice here, but almost all of these areas would show up with a fuel smell all the time, or while the car is running - it doesn't happen. Only about 10 minutes after shutting off, which is what is slightly confusing to me.

    I'll have to take the car out and let it idle for a while and see if I can smell gas - last time I did that, I couldn't smell anything. In general, if I smell gas while driving or idling, I don't drive the car.

    On a side note, I now have two Halon fire extinguishers in the car, which I think should be a requirement for all cars. One in the trunk and one under the passenger seat. I used a small one for under the seat and a big one in the trunk. I grabbed two from our stock of these:

    http://www.drivewerks.com/catalog/Safety/H3R.htm

    -Wayne
     
  8. Ken

    Ken F1 World Champ

    Oct 19, 2001
    16,078
    Arlington Heights IL
    Full Name:
    Kenneth
    Check your headers. A small gas leak on them will evaporate when they're hot (or burn). When they cool off you'll smell it. This happened to me on my Lotus. Of course, this is an EXTREME fire hazard so fix the leak!!!!

    Ken
     
  9. f355spider

    f355spider F1 World Champ
    Rossa Subscribed Owner

    May 29, 2001
    16,558
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    Hugh G. Rection
    I noticed the gas smell in my previous carb 308, I tracked the smell down to the air intake on the passenger side. My mechanic said it was caused by him removing all the vapor recovery plumbing, and not to worry about it....I don't have the car now, so not a concern. But thought about hooking it all back up.
     
  10. Wayne 962

    Wayne 962 Formula Junior

    Nov 27, 2003
    407
    Two very good comments - the header one especially. That is a good point. I will have to take a close look at the car when I park it after driving next time...

    I assuming though that a really bad fuel smell would not be considered normal on these '79 cars?

    Thanks!

    -Wayne
     
  11. pma1010

    pma1010 F1 Rookie
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    Jul 21, 2002
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    Philip
    Wayne
    It is not normal on a carb'd car.
    Philip
     
  12. donaldh2o

    donaldh2o Karting

    Nov 10, 2003
    143
    Irvine CA
    Full Name:
    Don
    Highly suspect the carb hoses. They can leak onto the intake manifold which can get dried out while driving the car, then leak for a few minutes after car is shutdown. Bad carb hoses don't leak until the fuel pump puts pressure on them.

    Just replaced all my carb hoses with Gates fuel hose (5/16", I think) and new Gold Seal (Made in the U.S.) clamps from Lowes.

    My carbs ('76 308) have brass washers and had to rough sand them to stop the leaking. I did not know about the fiber washers. What is the original Weber part, fiber or brass?

    Also replaced filler hose with a new hose from Ferrari.
     
  13. pma1010

    pma1010 F1 Rookie
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    Jul 21, 2002
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    Donald
    Fiber is the way to go. You can get them to seal with the cu. but it is harder.
    Ferrari part.
    Philip
     
  14. snj5

    snj5 F1 World Champ

    Feb 22, 2003
    10,213
    San Antonio
    Full Name:
    Russ Turner
    Two experiences with increased gas smell.

    first was a hose disintegration where the hose fastens to the tank, reachable through the right wheel well; no dripping, but the fuel return hose was soaked where it bent away from the nippled tube.

    second was when the fuel tank ventilation system (evaporative emmissions) was disconnected - this generates a noticible increase in gas smell. May want to check these connections as well.

    hth
    rt
     

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