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#1
03-20-2014, 02:39 PM
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High vacuum pressure on fuel cap
I'm not sure if this is normal or not, but I have a lot of vacuum -just after driving -in the gas tank. This is for my 1973 220/8 gasser. It seems to suck the fuel out of the carb bowl when allowed to sit for a couple days. Does this mean the fuel vent valve for the tank is not working? I have the Weber conversion carb. I don't remember this problem with the Stromberg.
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Dan 1981 240D 1987 300D Turbo 1973 220 Das Beste Oder Nichts 
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#2
03-20-2014, 03:50 PM
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Vacuum in the tank is not normal. The vacuum lines are connected incorrectly. The line from the tank is for low atmosphere not vacuum. The line coming from the tank should be connected to the breather assembly.
Post a picture and I'll try to figure out what you can do to alter your set-up to work properly.
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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.” ― Brian P. Cleary, You Oughta Know By Now
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#4
05-27-2014, 05:51 PM
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Isn't it also possible that the "return pot" in the tank is clogging, not allowing fuel to return and causing a vacuum in the tank as well? Something to check if so.
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1962 220SE W111 Coupe, 2nd owner http://img.photobucket.com/albums/v3.../SideSmall.jpg The Coupe Group (W111/112 coupes and cabs) official website The Coupe Group on Facebook MotoArigato: Roadworthy News & Humor
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#5
05-28-2014, 07:58 AM
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Quote:
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#7
05-29-2014, 01:05 PM
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Many years ago I knew someone who had this problem on a diesel. It turned out to be a bad vent in the fuel cap.
Of course if you ran with no fuel cap this would 'solve' the problem but short of that you might try a new cap and let us know if it helps. And this will need solving. It is possible to draw such a vac that your tank will deform from the outside pressure.
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#8
06-04-2014, 11:32 PM
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Thanks for all your ideas. Once running, it runs very well with no hesitation hot or cold. The weber has a return line which is connected (like the stromberg). The supply and return lines are physically located higher than the fuel bowl.
I drilled a small hole in the gas cap. It had no effect other than preventing a buildup of vacuum. This would suggests that the fuel bowl is being emptied for other reasons - not vacuum.
__________________
Dan 1981 240D 1987 300D Turbo 1973 220 Das Beste Oder Nichts
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#9
06-05-2014, 08:31 AM
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Some vehicles are more prone to losing fuel through evaporation than are others. The problem is worse in warmer areas and with the changed formulation of modern gasoline.
Are your Webers attached directly to the intake manifold allowing heat transfer following a drive? If so, this will increase your evaporation potential and you may want to consider installing insulating gaskets to keep the Webers cooler.
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#10
07-02-2014, 07:11 PM
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Quote:
Is this related to a fuel line vacuum issue?
__________________
Thomas Viano '72 280 SE 4.5, over 100,000 miles
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