Zenith will flood the engine constantly

Just to give y'all an update I did finally get to rebuild my carburetor. Took it apart and it looked good on the inside. I checked the passageways with wire and compressed air and everything is clear. Put the rebuild kit in and snugged everything in. Unfortunately it does still leak quite a bit from the bottom hole near the choke plate.

I got a message from a member on here offering to help me. I'll talk to him and let you guys know of any developments.
 
Mike, I had a problem with the main and cap jet leaking at their bottoms where they set on their gaskets. The main is underneath and the cap is on the venturi side. I set the bottom half of the carb on the bench and shimmed it to level. I added a small amount of fuel to the bowl and watched over time for a leak at the gaskets base of the jets.



I had to use the black gaskets to get them to seal. The reds would not work. They are of different materials. Others since, have suggested some gasket sealer on the tiny gaskets before installing. Others have smoothed out the bottom with milling / drilling bits???
 
Years ago, I chased a pesky leak from a Zenith for weeks, going through all you have done. A very frustrating experience. It turned out that there was a crack in the body radiating from the main jet hole. The fuel was leaking past the brass plug and gasket through that tiny crack that was almost impossible to see. I had thought the fuel was coming from the carb's intake throat and was running down to the lowest point on the carb = the main jet plug. I deduced that air rushing past the carb while driving was forcing fuel to migrate towards the open intake throat, dripping from there once the car was stopped. I had been looking in the wrong spot. The only way I found the crack was to glass bead the lower body AGAIN and inspect the result closer. And there it was! Apparently in an effort to stop a leaking carb, someone in the past had over-tightened the main jet plug, cracking the delicate metal. The crack started inside the hole just below the plug and was even in the threaded portion. It then spread outwards in the lower casting, which is where the gasoline was leaking. It was faint, but the lower casting definitely was cracked. I replaced the lower body and transferred all the new and checked-out parts to the new carb half and the leaking problem was solved.
Check that your lower casting isn't also cracked in that area. Dripping fuel from the carb's throat fooled me into thinking the problem lay there. Who'da thunk that the lower casting was hiding a hairline crack? That's only example I have ever seen of this. And of course, it happened to ME!
Marshall
 
You guys are providing some interesting stories and useful tips. I'm going to check for leaks with the new gaskets as Bob has just suggested. But this may not be the problem. After tightening some of the jets and the float valve, I noticed that it started coming out of the overflow port on the engine side of the carb (indicating that the bowl was way over full). I said "the heck with it" and decided to start the car after closing the fuel shut off. After running the car and turning on the fuel shutoff valve I had no drips, even after turning off the engine.

I don't think this is permanent because I had this happen before I rebuilt the carb. Unfortunately the car idles only mediocre even after some GAV and mixture adjustments. When it gets warmer here in New England I'll drive the car and see if it's any better. If all else fails I'll see if I can try a good carb from one of my club members and see if maybe I have other issues.
 
If the engine had been running rich because of the carb constantly flooding, you might want to remove the spark plugs and clean off any soot that has developed from unburned gas. That may be why the engine isn't idling well now.
Marshall
 
Mike 1291 , you state in post #3 that your engine runs well at speed but dies when you take your foot off the accelerator. Same symptom happened to me while on a tour. I ran out of gas near a gas station and refilled gas. Started up engine ,ran well until the first stop light,engine died. Got it started ,ran on to our motel where I had lots of experts suggesting on how to fix my problem. I removed the idle jet , looked through it ,but couldn’t see daylight. Took it into the motel and with my toothbrush and hot water I easily removed some crud that was probably picked up whe the tank was low. Won’t do that again, always have the pencil filter in your tank,I didn’t, and get fuel before you need it. The only reason that the car died was crud in the
Idle needle, a very easy jet to check before you change a bunch of stuff.
Don S
 
Don S said:
Mike 1291 , you state in post #3 that your engine runs well at speed but dies when you take your foot off the accelerator. Same symptom happened to me while on a tour. I ran out of gas near a gas station and refilled gas. Started up engine ,ran well until the first stop light,engine died. Got it started ,ran on to our motel where I had lots of experts suggesting on how to fix my problem. I removed the idle jet , looked through it ,but couldn’t see daylight. Took it into the motel and with my toothbrush and hot water I easily removed some crud that was probably picked up whe the tank was low. Won’t do that again, always have the pencil filter in your tank,I didn’t, and get fuel before you need it. The only reason that the car died was crud in the
Idle needle, a very easy jet to check before you change a bunch of stuff.
Don S
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I believe the reason I had that issue is because opening the throttle let in more air and thus it ran better with the excess fuel. Plus it straight out died before if you even thought about letting off the gas. Everything is new now and my gas (and gas tank) are very clean, so there shouldn't be any problems with contamination.
 
A couple of things to check. .....The throttle shaft,is it sloppy? Are you using a thin or thick base gasket, this can change the fuel Level in the bowl. Try using original jets, that's all I use.
Are all the surface areas flat, especially where the carburetor and intake bolt together.
Remove the intake, I have found them cracked and pitted where they meet the block.
Are you running a original fuel line with no filters or shut off valve added.
What about a air filter? You can also try another carburetor.
Remember everything is 90+ years old, carburetor parts have been swapped and reproduced that long.
Sometimes bad parts get sold over and over at swap meets.
 
The only thing original on the carb is the core itself. All of the removable parts are new except for the secondary well, choke, and throttle which appear to be in good shape and have no obvious wear. I also sanded down the two carb halves before assembly and checked for gaps with a .002 feeler and didn't find anything concerning.

The plugs are good but I did notice some carbon buildup in the engine. Thick on the front and progressively less as you look at 2, 3, and 4. Could this also cause some issues?
 
Assuming the piston rings and valve seating are consistent between the four cylinders, keep in mind that #1 cylinder almost always runs cooler than the cylinders behind it because it is in front and is the recipient of the air rushing through the radiator as the car moves. This air cools the front of the engine block more efficiently than what #4 receives. Consequently, #1 cylinder runs cooler and its spark plug tends to carbon up sooner and more dramatically than in the other cylinders. Your engine shows signs of this fact, in that you write that the carbon build up is less in each successive cylinder moving from front to rear. #4 cylinder is farthest away from the radiator and fresh air. It tends to run hottest because of this (and probably due to the close proximity to the rear of the exhaust manifold and exhaust pipe), so the spark plug is usually cleaner and its electrode more tan-colored than #1 plug. This is all assuming the cooling system is working properly and the passageways around each cylinder are clear enough to do their job. Any cylinder with clogged or restricted cooling passageways will, of course, run hotter than it was designed to run, hence the spark plug will show signs of running hot, perhaps even turning the spark plug electrode white. Not good. Varying heat ranges of spark plugs will also affect sooting of the electrodes.
Unless one spark plug is really sooted up, the engine should run o.k., but possibly "skip" or run slightly erratic during idle. Clean all the plugs and check the gaps again. See if that improves the idle and misfiring. If not, you're probably still looking at a carburetor issue from your description of symptoms.
Marshall
 
It seems pretty clear to me that your float is set too high. That would explain every symptom you are describing. I find that on some Zenith carbs the factory setting is just plain too high. Take the top off and turn it upside down and look at the angle of the float. Most people think it should be level, that’s not correct. I wish that I could explain to you what and where to measure but I can’t really put it into words. With the stock Zenith setting the bowl is within a 1/16th of an inch of flooding all the time so believe it or not, just the thickness of the gasket between the 2 halves can make the difference (in theory, just adding another gasket could solve the problem but I wouldn’t go that route). I would keep lowering the float about a 1/16th at a time until either (A) your problem goes away, or (B) the engine starts to starve for fuel (surging, missing, backfiring). In my humble opinion, although the Zenith is pretty simple that float bowl level is too sensitive, a little more clearance in the design would have been better. You say you sanded down the 2 halves, that alone could be the problem.
 
I forgot to add that when the top is upside down the float should be sloping upwards. 1 5/32” should be the measurement between the casting of the top to the float seam (if you can understand what I’m saying). I have found many, many Zenith’s that will flood if the float is set to factory specs. For parts, contact David Renner at Renner’s corner. He flow tests every jet before shipping it (and he makes them himself)
 
jeepguy1948 said:
when the top is upside down the float should be sloping upwards. 1 5/32” should be the measurement between the casting of the top to the float seam (if you can understand what I’m saying).
Click to expand...

So where should this measurement be taken? At the high end of the float? The low end? The middle?
 
I measured my float and it's 1 3/32 from the base as it sits after sanding the top and bottom halves. It's a tad higher than Les Andrews book but less than others who say that 1 5/32 is the measurement. I'll try and add another gasket.

Honestly I don't know how anyone can drive an A on any sort of hill if the float is that sensitive.
 
Well Mike, when you are going downhill the fuel runs to the front of the bowl and creates fuel starvation but since you are going down hill you don’t need the fuel anyway (if engine dies while going downhill at idle that’s the problem). When you are going uphill there is a tendency for the carb but since now you are now going up hill and need the fuel, it works. I don’t know that it was designed that way but it seems to work out. A Zenith carburetor can bee a nightmare of won’t work right, won’t work right, won’t work right, and then boom, you finally find the perfect set up and it works great. I have a had problems with many Zenith carbs that were supposedly “rebuilt” by “professionals” and when I open them up, a thrown together mess. People swear that the Marvel Zenith replacement carb (from the Marvel Mystery Oil guy) is superior and easier to deal with. They aren’t hard to find. If you want to stay with an updraft carb but are not married to 100% stock/original that might be the way to go. Some Zenith bodies seem to be unusable after 90 years (of “Bubba” maintenance and abuse) and you have to try more than one to get a winner, that’s just the way it is.
 
Yeah I think you have a good point, jeepguy. I thought that it would be nice to try to get an original carb working. When I got it passed down to me it had a Tillotson on it so I guess going to another updraft would be okay with me. I never really liked the Model A Zenith's float design anyway. I do have a model B Zenith that I could also rebuild if this doesn't work. At least it's a cast iron Zenith.
 

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