4100 Carb leaking raw gas onto manifold

[mammentorp]

63 with original 4100 carb seems to be leaking raw gas onto outside of intake manifold. I just discovered this problem after taking the car for a short drive. (Ironically to go fill it up with gas.) I have a kit and am planning to rebuild this carb in any case, but wondering if anyone has guidance on troubleshooting this problem in advance? Seems to be leaking gas out on both sides of the carb, filling depressions in the manifold.

[Alan H. Tast]

1. Check carb float adjustment and set to factoryspecs (info should be in rebuild kit instructions).
2. Replace needle/seat assembly.
3. Check fuel delivery pressure from pump to carb. Modern gas is notorious for creating a higher pressure which will force gas past the needle/seat.
There could be other things like worn throttle shafts/bushings, heat-soak, ad infinitum, but look at the simple things first.

[mammentorp]

Thank you Alan. Do you think I should consider adding a pressure regulator to the input line depending on what I get after the rebuild?

[aa010175]

I had the same problem last year on my 1962 Cadillac. The floats were stuck and there for they would not shut off the fuel when the float chambers were full. I taped on the carburetor with a small plastic hammer. Don’t do it unless you know where to tap. It’s not the correct way to fix it but it worked for me.

[Aaron65]

It could also be leaking from the power valve underneath the front float bowl. Either way, you should put a kit in it. Good luck!

[mammentorp]

Thanks again all. I'll work on the rebuild and report in.

[Alan H. Tast]

Thank you Alan. Do you think I should consider adding a pressure regulator to the input line depending on what I get after the rebuild?

Take care of the simple things first, a rebuild being one of them. The power valve noted by another responder is also good to do and should be part of the rebuild kit. I would still check to see what the fuel pressure is just for comparison or as a 'marker' and report back to us what you find. I don't have a lot of experience with pressure regulators and such but know people who've had major issues with fuel pressure going back to the 1980s, when I first saw one installed on a '63 convertible in an area where ethanol was starting to become predominant.

[mammentorp]

I completed the rebuild of the 4100, and am pretty confident I did things correctly. Bolted everything back on and tried an initial startup last night. Not good. I had the air cleaner off the carb, and as the engine turned over, gas was spewing out of the secondary side of the carb and all over the intake manifold. I could literally watch it spraying out of the carb, and again the intake manifold got soaked.

Now, I could have messed up the rebuild, but I've rebuilt dozens of carbs over the years and my batting average is strong. And it's hard for me to think what could have gone wrong with the rebuild that would cause this symptom. So I feel as though I have to now look at pressure from the fuel pump. I do live in Wisconsin, so there's no ethanol in the premium gas I buy. But too much pressure from the pump is the only thing I can think of that might cause these symptoms.

What am I missing??

[Alan H. Tast]

I completed the rebuild of the 4100, and am pretty confident I did things correctly. Bolted everything back on and tried an initial startup last night. Not good. I had the air cleaner off the carb, and as the engine turned over, gas was spewing out of the secondary side of the carb and all over the intake manifold. I could literally watch it spraying out of the carb, and again the intake manifold got soaked.

Now, I could have messed up the rebuild, but I've rebuilt dozens of carbs over the years and my batting average is strong. And it's hard for me to think what could have gone wrong with the rebuild that would cause this symptom. So I feel as though I have to now look at pressure from the fuel pump. I do live in Wisconsin, so there's no ethanol in the premium gas I buy. But too much pressure from the pump is the only thing I can think of that might cause these symptoms.

What am I missing??

Did you thoroughly clean out all the passages in the carb casting?
Were the adjustment needles set properly for the secondaries?
Is the float adjusted to the correct height for the secondary bowl?
Is the float and/or needle valve binding and preventing them to work properly?
Did you also replace the seat for the needle valve? Are there any burrs or other deformities that would keep the needle valve from seating fully?
Is the cover for the power valve 'dead-flat'? These can get warped - a few passes of the cover over some fine wet-dry sandpaper on a piece of glass should reveal if there's any high/low spots. Same goes for the carb base.

Pictures would be good to see what you're dealing with.

[Cliff Rankin]

My money would be bad float, or needle / seat. Or it’s not set correctly. You can check this without pulling it back off.

[Rusty57]

I had a similar issue with a newer model 4100 carb. It has externally adjustable floats. The fuel would continue to flow into the bowl even though the needle valve was seating properly and shutting off the inlet.

The problem was bad o-ring seals on the seat assembly. I replaced the assemblies and the problem was gone.

[mammentorp]

It will be a few days before I can get back to this project. I will lift the lid on the carb and double check the floats and needles and seats. Those parts are all brand new with the carb kit. And if I have the same issues I'll try and capture a video.

[Cliff Rankin]

While I would love to see the video as it’s hard to help from an arm chair. May I suggest , slow down , capture a beer. It’s all about enjoying the hobby and having fun.
I will watch this thread and help where I can. I’m not a
T Bird expert. Just an old Mechanic with old car disease
Cliff

[claybreaker 144]

Put a pressure gauge between the fuel pump and carb, should be less than 5 psi.

[Alan H. Tast]

One of the other websites I go to on a daily basis is "The Ford Barn" (as some of you may know) as I also have a '40 Ford project and a '55 Fairlane Victoria (NOT a Crown) hardtop. Earlier this afternoon I was looking over a post dealing with problems of higher fuel pressure.

https://www.fordbarn.com/forum/showthread.php?t=321254

Several commenters remarked that newer (re: 2019-newer) carbs and pumps are coming from the People's Republic of (Red) China. The pumps typically are exhibiting high fuel pressure vs OEM-specs, and to make matters worse are typically not rebuildable. There were at least three suggested ways to deal with high-pressure issues:

1. Recommendation was to have an original pump rebuilt, provided you can find a person to rebuild and use parts compatible with today's alcohol-laced fuels. That's the easy fix.

2. Install a fuel pressure regulator. While I suggested that earlier, commenters in the Ford Barn thread are saying that the regulators that are out there today, whether they be from Holley, Mr. Gasket or similar. Often the comment was the regulators would only last for about a month before they would crap out.

3. Install a bypass line from the carb back to the gas tank. That involves dropping the tank and installing a small hose nipple for the return line to attach to, along with plumbing a line from the gas tank up to the area of the carburetor. There was a recommendation posted in the thread on how to do a bypass-return via the fuel filler pipe versus modifying the tank, but I don't have access to that document right now.

4. Use an electric fuel pump with a lower pressure rating and bypass/abandon the mechanical fuel pump. This would also require installation of a bypass line to run fuel back to the gas tank.

One commenter offered this:

I don't think new fuel pumps for Y-block and FE engines have been any good since the late '90's. All the brand X fuel pressure regulators are failures. A top-of-the-line Holley won't be able to hold back the high-pressure longer than a month on cars driven daily.
Currently, none of the repro parts suppliers are offering rebuild kits for Y-block/FE 8's and mileage-maker 6's original fuel pumps. And if they did, I wouldn't trust em to be any better than buying one of the foriegn-made new pumps.

Solution: if High-fuel pressure exists, get a Wix bypass fuel filter for a Mopar car and install it ahead of the carb. Place a piece of smaller tubing INSIDE the carb inlet tubing as an orifice to cause gas to back-up into the Wix bypass. Run a whole new line of tubing from the Wix to a new port at the top of the gas tank for fuel return. Now your carb will not flood out at idle.

A little more searching on another website I go to daily, The Hokey-A$$ed Message Board (HAMB), offered more info on the bypass fuel filter:

https://www.jalopyjournal.com/forum/thr ... p.1153558/

One person commented: "33041 Wix has an .057 orifice, as I measure it with number drill bits. 1/4 return line, 5/16 main lines"

A follow-up from another person commented:

I think .057 is close enough to .060, which is, I think, what the general consensus of what the orifice is on these filters?

If I need more pressure drop, I figure I can just drill out the hole little-by-little as needed?

I've got an electric pump that's advertised as 4.25 -6.25 lbs., and with gauge it's 3-5.75 lbs. on my setup. I'm just trying to get the idle pressure a little lower and don't care about cruise pressure because i rarely rev above 3000 for any length of time. Quadrajet. 2.56 rear---hence the lower rpms.

WIX bypass fuel filter - Late '60s-'70 Jeeps

The type of filter was OEM on Jeeps from at least 1968 through the '70s, and on MoPar products (M- and J-bodies) in the '70s and '80s.

Another filter is the Baldwin BF930:

Baldwin BF930 Bypass Filter (zoro.com)

Baldwin BF390 Bypass Filter Specs (zoro.com)

I'm having a problem visualizing how to add a smaller orifice/restrictor in the fuel line, other than slipping a smaller tube inside the 1/4"-line feeding the carb from the pump either at the carb (outlet) end or pump (inlet) end. A person could modify an existing steel line and splice in the bypass filter between the pump and the carb, or fabricate a new two-piece steel line and place the filter somewhere inline where it will be easily accessible and won't be bothered by engine heat or interfering with the distributor or air conditioner compressor and bracket. You'd still have to run the return (vapor) line back to the gas tank.

Personally, I recommend using steel line with short rubber fuel hose connectors between the filter-line and line-tank return inlet. I cringe at the thought of using 7-feet worth of fuel hose on the underside of the car that can be easily punctured or cut by road debris.