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Fri Oct 21, 2011 4:43 pm

I have a 40 Weber IDF early style Italian carb with the cam style accelerator pump. I cleaned and rebuilt the carb. The car runs but I get pooling of fuel on top of the throttle plates when i turn it off. And it kinda gurgles. Any ideas where my leak is? Thanks.

Fri Oct 21, 2011 6:20 pm

I had a new Spanish made 44 IDF that leaked with the engine off until the bowl was empty. Gas would pool on top of the throttle plate even with the fuel line disconnected. The carb was bad. It either had a casting flaw or a passage was drilled wrong.

Did you just install the carb, or was it working OK until recently? You can remove the carb, take the top off, and pour some fuel in the bowl. It should not leak out.

Fri Oct 21, 2011 7:16 pm

This carb is one of 2 I purchased off the Samba or Ebay. I forget. So I haven't used it prior. I disassembled, cleaned and rebuilt it with new gaskets, o-rings and needle valve. Set the float at 11mm. Now I have this leaking issue upon installation. I'll get some gas in the gas can tomorrow, take the carb off and fill the float bowl and see if it leaks. Thanks.

Fri Oct 21, 2011 7:44 pm

use liquid dish soap and air pressure to find the leak makes it easy & safe.but dont blow out any parts across the room(like the choke thingies)it is much safer than waching gas drip,and you still cant see where the gas is dripen from

Fri Oct 21, 2011 8:09 pm

See if it is dripping from the nozzle on the auxiliary (booster) venturi, or if it is coming out of the progression holes. Is it just the one barrel?

Fri Oct 21, 2011 8:12 pm

It's a 2 barrel.

So if I use dish soap in the bowl where should I be blowing the air in from. I know from outside but where exactly?

Fri Oct 21, 2011 8:19 pm

Bikerchris wrote: It's a 2 barrel.

So if I use dish soap in the bowl where should I be blowing the air in from. I know from outside but where exactly? He meant is it only dripping/pooling in the one barrel of the 2 barrels or is it pooling in both of the barrels of the 2 barrels? Kind of redundant way of writing but I hope the question is now clearer.

RC

Fri Oct 21, 2011 8:22 pm

Ohhh....It was just one barrel originally. Then I took things apart and cleaned adjusted, etc. And now it's pooling over the throttle plates on both barrels.

Fri Oct 21, 2011 8:24 pm

well shoot, I guess the grime was plugging the leaks :lol:

Looks like you'll have to take that carb off and do some bench testing

Fri Oct 21, 2011 8:28 pm

Buy some JB Weld and do the Mctuckey thing while you're at it.....can't hurt and might help.

Did you check WHERE the gas was coming from that is pooling? Bet the seller all ready had trouble and was unloading the carbs. Spends your money and takes your chances.....

RC

Fri Oct 21, 2011 8:31 pm

Well, that's just it. I can't really tell where it is coming from. So I thought I'd ask here and see if others had a similar issue.

Fri Oct 21, 2011 10:50 pm

No doubt this is fouling the plugs on that side of the engine. I had the same problem with my old bug. After taking the carbs apart half a dozen times, I looked at the fuel filter and the filter element looked expanded with no air bubble in it. Replaced the fuel filter and the problem stopped. I haven't heard if the problem persisted after the car was sold.

Sat Oct 22, 2011 5:44 am

If it is coming from both barrels I would suspect a fuel control problem, not a defect in the carburetor. Have you checked your fuel pressure, and have you given the inlet valve a close look? How about your float setting?

Sat Oct 22, 2011 6:40 am

The fuel filter is new and upstream from the carbs so it isn't that. I have a stock Brazil mechanical fuel pump, and the other carb doesn't leak. The float is set at 11mm. I can blow through the inlet valve but I'm not sure that means anything. Does it? Love your carb clinic page by the way. Great pics there.

Sat Oct 22, 2011 6:47 am

When you have a pressurized system with more than one relief (the inlet valves), it is possible for one to leak and the other not.. Suppose that the over-pressure situation is small, and of one inlet opened up, it would be sufficient to relieve the over-pressure to the point that the other inlet valve is not overpowered. Pumps have two physical characteristics that play into this. One is flow and one is pressure, and they interact in a way that can be modeled and used to rate their performance at different pressures. This is why a lot of pumps of various kinds are rated with a flow at a specified pressure. Fuel pumps are no exception. So a pump could have a pressure at NO flow that is high, but when relieved, even a little bit, may go significantly lower. It's very common for only one carb of two to leak. A powerful pump can make both do it.

Being able to pass air through the inlet valve means it will open. ;)

Sat Oct 22, 2011 7:38 am

Ahhh....that makes sense. I have this fuel pump.

Sat Oct 22, 2011 7:44 am

I had a similar problem on some 44IDFs. Fuel kept puddling in the throttle plate. The fuel pressure was dead on and the needle and seat valves sealed up like a drum. I spent a good long time looking at that carb with a jewelers loop to try and find the problem. I found nothing visibly wrong. I ended up calling the distributor we bought them from and after a long drawn out process they sent another carb body. That did fix the problem so I can only assume it was a defect in the casting or something.

Sat Oct 22, 2011 8:21 am

So I was thinking...I actually have 3 of these carbs. Two of them have the same problem. Those 2 I rebuilt with a kit off ebay that came from Italy. The seller was very specific to make sure I got the right pieces, so I bid with confidence. Anyhow, both the leaky ones have the same leaking problem with the same parts and the third carb does not leak with a needle valve from a different source. Maybe I could try switching the needle valve around. I find it hard to believe that I have 2 early Italian carbs with casting flaws that have been around for a few decades and probably worked well for somebody at some time.

Sat Oct 22, 2011 8:53 am

Additional info

The gas pooled on just one throat, so that was a clue. Not likely to be the float setting or needle. Both had been checked.

My engine started and ran OK, even went through dyno breakin. The leak was slow enough that it apparently did not make that cyl rich enough to notice. So, some people could run one of these leakers sorta' ok, and only noticed the leak if they looked down the carb throat with the engine off. If that was the case then they were constantly washing down that cylinder.

The best final evidence is on the bench with the top off and some gas in the bowl up to about 3/4 full. It should not leak out. This eliminate fuel supply, float setting and the needle as a source.

Sat Oct 22, 2011 2:16 pm

Update:

It appears it is leaking/bubbling from the side by the pump jet. Although it is not the jet itself. Bubbles are further down. I took the carb off the motor and filled the bowl 3/4 full. No Leaks. So the carb body is good. Same with my other carb. There was a bit of a leak by the gasket between the carb body and intake manifold. Could that be the issue?