Weber 40 IDF Leaking

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Miles Richardson
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Weber 40 IDF Leaking

#1 Post by Miles Richardson »

I drove my C Coupe a few weeks ago after a few weeks of sitting, and later that day I noticed a strong gas odor in the garage. Upon looking around the engine bay and then underneath the car, I noticed a wet spot under the left side of the car. I finally realized after looking at the engine bay again that the left carb was noticeably wet and it was leaking gas at the screws at the accelerator pump.

I have heard this could be a bad pump diaphragm or the needle valve could be stuck causing fuel to continue to flow as the car sits. The fuel petcock has been closed as it has sat and the gas drip stopped, but it started dripping again today after moving the car.

I have Weber 40 IDF's. Any ideas of what the issue could be? Is it something that would require the carb to be removed to fix?

Thanks in advance!
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C J Murray
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Re: Weber 40 IDF Leaking

#2 Post by C J Murray »

Be careful about starting the car!!! Turn it over a few times by hand before attempting to use the starter to fire it. You could be hydraulic locked with fuel in the cylinder and this can cause a bent rod if started. If you can't turn it a few revolutions with a wrench then remove the plugs and turn it over(no ignition!) to extract the fuel. Sounds like a float problem.
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Miles Richardson
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Re: Weber 40 IDF Leaking

#3 Post by Miles Richardson »

Great point CJ. Thanks!
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Daryl Bruhl
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Re: Weber 40 IDF Leaking

#4 Post by Daryl Bruhl »

Miles, I have 63 super 90 with weber 40 IDF carbs and my leak at accelerator pump was torn diaphragm. Easy check, remove 4 screws and you can get to diaphragm and spring under square accelerator cover. Over the years this material develops crack at the folds and leaks. Same thing happens to your fuel pump diaphragm. Being in SoCal should find at local hot rod VW or performance shop. Buy two and replace other side also.
Enjoy
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Re: Weber 40 IDF Leaking

#5 Post by Jeffrey Leeds »

C J Murray wrote:Be careful about starting the car!!! Turn it over a few times by hand before attempting to use the starter to fire it. You could be hydraulic locked with fuel in the cylinder and this can cause a bent rod if started. If you can't turn it a few revolutions with a wrench then remove the plugs and turn it over(no ignition!) to extract the fuel. Sounds like a float problem.
OR, 35 years ago my first 911 had the dreaded CIS FI system. It was subject to vapor lock, which was a regular occurrence. The fix was to raise the fuel sensor plate to bleed off the trapped air so fuel would begin to flow again. If it was overdone it could lead to filling the combustion chamber(s) with raw gasoline a/k/n/a hydro-lock. The fix was to remove all spark plugs (6) and crank over the engine to blow the fuel out the spark plug holes. However, you had to remember to also disable the ignition system to prevent sparking at the ignition wire terminal ends. You can imagine how exciting it could get if a plug wire(s) ignited the gasoline that had been blown out of the cylinders that was laying about. You don't need to ask me how I know this.
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Miles Richardson
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Re: Weber 40 IDF Leaking

#6 Post by Miles Richardson »

Daryl Bruhl wrote:Miles, I have 63 super 90 with weber 40 IDF carbs and my leak at accelerator pump was torn diaphragm. Easy check, remove 4 screws and you can get to diaphragm and spring under square accelerator cover. Over the years this material develops crack at the folds and leaks. Same thing happens to your fuel pump diaphragm. Being in SoCal should find at local hot rod VW or performance shop. Buy two and replace other side also.
Enjoy
Daryl 63 super 90
Will I need to remove the carb to be able to remove this plate, or can I just leave it mounted? Do I need to worry about fuel spilling once it's off?
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Larry Coreth
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Re: Weber 40 IDF Leaking

#7 Post by Larry Coreth »

Caution pet peeve alert !

Jeffrey Leeds,

On CIS systems where the fuel pump is at the fuel tank, vapor lock of the fuel line is an impossibility since the line is under 60psi pressure. Now it is possible to boil the fuel if you get hot enough such as routing the fuel line very close to the exhaust, unlikely. But if you keep running the fuel pump it will push cooler fuel from the tank and condense the vapor (not air !!) bubbles. Never happened to me even on the hottest days on any of the cars I had with CIS, Porsche, VW Volvo. etc. of the late '70's -'80's era.

Whenever a CIS car I had, had a hot start problem, the solution was usually some part that had failed, system pressure check valve, insufficient system pressure (fuel pump), etc.

Remember "vapor lock" by definition occurs when the pressure on one end of a fuel line is lower than the other AND below the vapor pressure of the fluid for that temperature. This happens when you are sucking at the engine compartment the fuel from the fuel tank with little or no head pressure , i.e.. mechanical fuel pump. Result, the more you suck, the lower the pressure the more the fluid boils creating vapor bubbles (not air !!) and no fluid flow.

So be careful when throwing around such technical terms without a good understanding of the term.
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Re: Weber 40 IDF Leaking

#8 Post by Jeffrey Leeds »

You are right, of course, Larry. My mistake was to use "vapor lock" generally to cover all similar type events to point out the danger of leaving the ignition system live while trying to solve a fuel problem. Now in the specific case cited, the car had run out of gas on the highway and was towed in to the garage. The fuel tank was filled, but the system would not prime itself to start the engine. So bleeding the system was instituted to get fuel moving. The engine was started - after the fire was put out.

Since I owned and drove that particular car for more than 18 years I personally experienced fuel boiling and no-start conditions on a number of occasions, the most memorable at Road America during the 1984 PCA Porsche Parade in Appleton, WI. RA was used for the "autocross" and participants got three laps, but not consecutively. The temperatures were in the high 90's and engines were shut off after each run and thus allowed to heat soak for 30 - 45 mins before the next run. Fuel boiling was the order of the day.
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Re: Weber 40 IDF Leaking

#9 Post by Daryl Bruhl »

Will I need to remove the carb to be able to remove this plate, or can I just leave it mounted? Do I need to worry about fuel spilling once it's off?[/quote]

No need to remove carbs. The use of a stubby screw driver will do the job. Place a towel under carb to catch fuel, less than an ounce. Should be a couple videos on Utube that show fix.
Enjoy
Daryl 63 super 90
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Miles Richardson
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Re: Weber 40 IDF Leaking

#10 Post by Miles Richardson »

Daryl Bruhl wrote:Will I need to remove the carb to be able to remove this plate, or can I just leave it mounted? Do I need to worry about fuel spilling once it's off?
No need to remove carbs. The use of a stubby screw driver will do the job. Place a towel under carb to catch fuel, less than an ounce. Should be a couple videos on Utube that show fix.
Enjoy
Daryl 63 super 90[/quote]

So I pulled the top off and the float level seemed to be right. Then I pulled the accelerator pump cover off and this is what I found. I'm going to assume that pinch on the side caused the leak.
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Gerry McCarthy
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Re: Weber 40 IDF Leaking

#11 Post by Gerry McCarthy »

It is likely the fold in the diaphragm was caused by replacing it with th carb on the engine. You can't see what's going on. Remove the carb, secure it with the pump facing upward, install new diaphragm, cover, spring and screws finger tight. Lift pump lever to the point where diaphragm is flat. Wiggle cover to encourage diaphragm to protrude around cover evenly, tighten screws. The diaphragm is now under even tension all around, and will function as designed for many years. I don't believe this can be achieved with the carb on the car.
Gerry Mc

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