Zenith will flood the engine constantly

[Mike1291]

I have a Tillotson on my stock engine that been giving me some trouble. Fortunately, I have a Zenith-2 I can use that was rebuilt, albeit 30 years ago.

I thought that I'd try and put it on for the heck of it and the car does idle and rev nicely. However, the moment I start going down the road the car starts to putter out and dies. The only way to restart it is to open the throttle all the way and crank until it roars back. It also leaks gas from something other than the fuel line. I'm guessing that the car is flooding itself somehow.

I should probably give it all new gaskets based on the age of the rebuild, but I wanted to check the carb out and do a few tests. I found out the following:

-The float does not leak after submerging it in gas for several hours
-The float valve does not leak if I blow into the gas line inlet and press on the ball lightly
-The float is set properly (using Paul Shinn's inversion trick shows that the float is at the correct height).
-The main and cap jet do not leak gas if you leave gas in the carb bowl at the correct height (5/8 from gasket)
-The carb adjustment needle DOES, however, have gas pool in the cavity after where it and the carb driver meet if you leave gas in the carb bowl at the aforementioned height

Does anyone have any ideas/suggestions of what I should look for next?

[jb-ob]

Mike, While you will get 7 million suggestions, mine would be to blow carb cleaner down inside the main jet. If the main get is clogged, it will give you the stumbling you have on acceleration.

With carburetors it is a methodical process of one step and test, then move to next issue. Don't over think it, Ford did that already for us. Best

[Mike1291]

Thanks for the tip. I have no issues with acceleration, I should clarify. It dies when I let my foot off the gas. I have to keep the engine revving or else it'll die.

[nkaminar]

This is a really good site for the Zenith carburetor.

https://model-a.org/default.html

Click on Problem Solving then Symptoms and Causes.

[1crosscut]

Mike check for a leak at the manifold gaskets and at the gasket for the carburetor where it meets the intake manifold.
While the engine is running spray starting fluid all around the gaskets. If there is a change in engine speed you have a leak. If you do find a leak that must be fixed first.

Your float valve may still be leaking. Remove it and clean it well with carb cleaner or similar. Sometimes no matter how much you clean them they are scored and will need to be replaced.

[Mike1291]

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I agree that the model-a website is a good one. I've checked it out before but I'll go step by step.

I've eliminated the false symptoms with my previous work (new distributor, new ignition components, ignition timing is set) and ensured I have good fuel flow. I'm going to try checking the manifold and the carb gaskets today. I'll also try to check the float with the carb on the car by holding up the float manually with the bottom half off.

[Y-Blockhead]

Originally Posted by Mike1291

I'll also try to check the float with the carb on the car by holding up the float manually with the bottom half off.

I always check my float level on a running engine (this on a Marvel) after initially setting the static level. Renner's Corner has the level gauges for the various carburetors.

[1crosscut]

I'll also try to check the float with the carb on the car by holding up the float manually with the bottom half off.[/QUOTE]

Holding the float valve closed manually will exert quite a bit more pressure than the fuel level does on the float valve so it may not leak during the test but continue to do so after it is reassembled.

[Gary WA]

Originally Posted by Mike1291

I have a Tillotson on my stock engine that been giving me some trouble. Fortunately, I have a Zenith-2 I can use that was rebuilt, albeit 30 years ago.

I thought that I'd try and put it on for the heck of it and the car does idle and rev nicely. However, the moment I start going down the road the car starts to putter out and dies. The only way to restart it is to open the throttle all the way and crank until it roars back. It also leaks gas from something other than the fuel line. I'm guessing that the car is flooding itself somehow.

I should probably give it all new gaskets based on the age of the rebuild, but I wanted to check the carb out and do a few tests. I found out the following:

-The float does not leak after submerging it in gas for several hours
-The float valve does not leak if I blow into the gas line inlet and press on the ball lightly
-The float is set properly (using Paul Shinn's inversion trick shows that the float is at the correct height).
-The main and cap jet do not leak gas if you leave gas in the carb bowl at the correct height (5/8 from gasket)
-The carb adjustment needle DOES, however, have gas pool in the cavity after where it and the carb driver meet if you leave gas in the carb bowl at the aforementioned height

Does anyone have any ideas/suggestions of what I should look for next?

Is the GAV (gas adjusting valve) working properly? All jets need to be tight!!!

[WHN]

Zenith carbs are really easy to take apart, clean, and rebuild.

30 years old?

I would take it apart. Check the jets, blow out all passages, new gaskets, and you should be good to go.

I have a “NEW” Zenith 1 that’s been on our 29 for 40 years. Just needs to be adjusted every couple of years. Other than that, not one problem. Car runs great.

Enjoy the Holidays.

[Keith True]

First,that carb needs to come COMPLETELY apart,like it was never rebuilt.All those little gaskets under the jets dry up and crack unless they are immersed.Also,cleaning agents are all a little corrosive,and unless the carb goes right into service the passages will grow a little fur in them sitting around dry.Those tiny little holes in the sides of the brass secondary well will get green and grow shut sitting on the shelf.A 30 year old rebuilt carb is a good core to start from for a fresh rebuild.

[johnbuckley]

here's a check list for causes of Zeniths leaking
Problem: Remedy
1 Leaking/loose float valve gasket: Tighten/reseal/replace
2 Leaking float valve: (or crud stopping it sealing) Replace ( or clean up if possible )
3 Friction on float hinge: Loosen
4 Incorrectly set fuel level: Re-set
5 Hole in float: Repair or replace
6 Too many gaskets on main jet Check
7 Cap jet or main jet too short: Replace
8 Leaking/loose gasket at main jet: Tighten/reseal/ replace
9 Leaking /loose gasket at cap jet: Tighten/replace
10 Leaking or loose GAV housing threads: Tighten/ reseal/ replace
11 Leak at fuel inlet union: Tighten/reseal/replace
12 Loose/leaking gasket at strainer: Tighten/reseal/replace
13 Loose/leaking gasket at drain plug: Tighten/reseal/replace
14 Cracked housing/leaking passage plugs: Repair or replace

1-7 will generally manifest as poor running.
8-14 will generally not affect running unless there is excessive leaking.

[Mike1291]

I checked the manifold and carb gaskets with some starter fluid as recommended and there were no leaks. I did end up deciding to tear the carb apart. The gaskets were indeed hard and shrunk so really I'll add new gaskets. There's some discoloration on pretty much every internal part so maybe I'll go big and buy the $70 kit with everything in it.

[bobbader]

Three things to look for in the current parts array................

1. The GAV needle is too short to seat properly in the carb. There have been different length needles depending on the parts manufacturer over the 30 year period you mention.
2. The GAV needle is long enough but the bottom carb casting takes a screw in brass seat which was left out in the rebuild.
3. The rebuilder used installed the brass seat in the position of the Compensator Jet in the bottom of the bowl, passenger side rear (and vice-versa) The brass seat and the comp jet look similar, but the comp jet has a much bigger through hole.

[Mike1291]

Originally Posted by bobbader

Three things to look for in the current parts array................

Here's some pictures I took of the carb when I took it apart:

[johnbuckley]

1. There should be a gasket for the main jet. It may be still stuck in the casting ... have a good look . If there is no gasket it could be a cause of fuel leaking out of the back of the carb. 2. There should be a lock washer for the main bolt that holds the upper and lower bodies together. 3. The mesh filter is normally joined to the brass hex nut so it comes out easy (and works well!). 4 Don't poke any wire through the bras jets.. soak them in thinners and blow with an airline. Zeniths are delightfully simple ... well done for getting apart so well and excellent photos. Steve Pargeter's Carb book is very good and lots of info ( as well as opinions!) on this wesbite

[Keith True]

I don't see the secondary well in your picture.That will HAVE to come out to clean the passages,and the brass well itself.It IS in the carb body,right?

[johnbuckley]

well (no pun intended) spotted Keith. also comp jet and gasket need removing from bowl of lower body

[Keith True]

The pictures seem to have left town.

[Mike1291]

You're right Keith, I didn't take that out. I'll check for stuck gaskets as well.

As for the pictures I don't know what happened. I copied a link from my Google Photos but I guess that's not a good way to do pictures. I'll add then as attachments for future posts.

[Mike1291]

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.

[Rob Doe]

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???

[Marshall V. Daut]

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

[Mike1291]

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.

[Marshall V. Daut]

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

[Don S]

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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

[Mike1291]

Originally Posted by Don S

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

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.

[Wick]

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.

[Mike1291]

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?

[Marshall V. Daut]

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

[jeepguy1948]

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.

[jeepguy1948]

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)

[katy]

Originally Posted by jeepguy1948

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).

So where should this measurement be taken? At the high end of the float? The low end? The middle?

[Mike1291]

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.

[jeepguy1948]

Katy, the high end

[jeepguy1948]

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.

[Mike1291]

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.

[katy]

Thanks

[jeepguy1948]

Maybe I missed something, have we been talking about a Tillotson all this time? Not a Zenith?

[Bob C]

You might get one of thees fuel level gauges from Renner's corner then you know exactly where the fuel level is.
http://www.rennerscorner.com/carburetor.html

[jeepguy1948]

Yes, Bob is correct about the float gauge. I even have one but I had forgotten all about it.

[Mike1291]

Originally Posted by jeepguy1948

Maybe I missed something, have we been talking about a Tillotson all this time? Not a Zenith?

No, it's a Zenith

I attached some pictures of what it looked like when I took it apart. Have some more advice from members that I'm going to try. One is to put a plug where the float valve is and check for leaks. I'm also going to put some gas in and check for leaks in the jets. Only thing used from the old rebuild is the float, secondary valve, and GAV needle housing.

[Bob C]

I can't see your float to well but check out the link to Marco's
site about a possible problem with the float.

http://www.abarnyard.com/workshop/carb-1.htm

[Big hammer]

It looks like there’s a divot where the needle touches the float, we need a closer picture

[jeepguy1948]

There could be a dozen other problems hidden away in the depths of the 2 halves or there could be none (I would bet there are, I haven’t found one without at least one). But if it’s flooding it is either the float itself, the float level, or the needle & seat. I can’t remember the details but there are a lot of bad repop needles and seats. Contact David Renner at Renner’s Corner he will have every part you might need (for Zenith, Tillotson, and Marvel) he agrees with me that the Marvel is the easiest to sort out and get the best performance from.

[Mike1291]

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Originally Posted by Big hammer

It looks like there’s a divot where the needle touches the float, we need a closer picture

It looks like someone repaired the float in the past. After testing it I can confirm that the float is airtight. But with my float being the way it is I'll need to measure the float level using the external measuring tool that was shown on this thread.

[jeepguy1948]

If the repair added weight (the solder maybe?) that could be the problem right there

[Mike1291]

Originally Posted by jeepguy1948

If the repair added weight (the solder maybe?) that could be the problem right there

It very well could. I'll get another float and see if it makes a difference.

[1Cobra427]

I am considering rebuilding the Zenith carb as it is leaking after long sit w/ previous owner and I am new to Model A's, I have never rebuilt a carb, I see the kit on Snyder's site for $71, am I better off to attempt myself or find someone to rebuild for me, not familiar w/ intricacies of internal carb parts!!

[Mike1291]

Originally Posted by 1Cobra427

I am considering rebuilding the Zenith carb as it is leaking after long sit w/ previous owner and I am new to Model A's, I have never rebuilt a carb, I see the kit on Snyder's site for $71, am I better off to attempt myself or find someone to rebuild for me, not familiar w/ intricacies of internal carb parts!!

I bid you good luck! This was my first one on any engine. If you have a little mechanical experience and some common sense I'm sure you'll do fine

[Gene F]

You know all the horror stories about old gaskets being stuck under the jet surfaces, when the jets come out, right?

Not really a lot to go wrong with these once you get them apart and cleaned.

That long jet in the middle when assembled has a dip in the tip to keep gas from syphoning out when you park the car for errands... So check that while you have it apart.

[jeepguy1948]

Buy a kit from David Renner at Renner’s corner. He manufactures many of the parts and test’s everything. On top of that he is a really great guy that knows what he is doing and is very helpful. Unfortunately he no longer does rebuilds himself but I’m sure he would recommend someone if you asked.
There are basically 3 things involved in a rebuild (1) the best quality parts (2) getting the body clean (this can be very, very difficult there are several passages that can’t really be reached without a lot of experience or drilling the brass plugs out) (3) getting the float level correct. I will stick with my comment that many of the bodies have been damaged beyond what an amateur can repair. If you decide to have in done by someone who will gaurantee the rebuild and actually road test’s each carb he rebuilds (some will try it on their car stationary in the barn but that’s not good enough). I helped a new owner that had purchased 3 “rebuilt” carburetors. I managed to make one decent carburetor using pieces from all three.

[Bob C]

X2 on Renner's.

[jeepguy1948]

Bert’s sells a rebuilt carb that they road test on their own cars, and Bert’s would stand behind it $300 with $100 core charge (so $400 if you don’t have a core). I think this would be one of the best ways to go if you don’t want to tackle it yourself.