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.