Zenith troubles

[History]

I rebuilt the zenith 2 a few months back and some of you may recall that I missed the passage on the side of the (gav). When it made no difference while adjusting the (gav) I opened it back up and found that passage was blocked and cleaned it with a paper clip.

On the initial rebuild, it started great, ran great, idled great but there was no change at all when I adjusted the (Gav). The OCD in me (hidden very deeply) couldn't stand it and I took it apart again to fix the (gav). I know that my float was set wrong initially as gas was coming out the vent in the bowl. I also noticed that the float had been adjusted but bending it and not adding washers. I was able to fix this with no added pressure or tension on the float (no float leak). I checked the float level by holding a jelly jar under the float and had my brother turn the gas on. I watched as it filled up and stopped with about 5/8 distance from the top. I figured perfection and put everything back together. It cranks the same but it doesn't run the same. It acts like its starving for gas as the acceleration isn't the same and it backfires some now. My flow from the tank to carb has been checked and it's good so,,,,,,,,,,. What say you experts, what should I check next?

[Bill G]

If it is starving for fuel, which is what it sounds like, I would check to see that the comp jet is not blocked by the secondary well; check to make sure that jet, the cap jet and the main jets are not clogged with debris. Or the passageways for that matter. How is it just idling?

[jquinlan]

After dealing with a leaky zenith carburetor by shimming up the float to the correct level, I was able to stop the carburetor from leaking and the car ran pretty good. However, one new problem that I started having was I would stall when coming to a stop unless I adjusted the idle on the steering column higher.

Last week we took our Model A to the Sweet Home Alabama tour and after mentioning this to a friend there, he asked how much of a turn did I have my gav. I told him I had it just a tad open and he said to experiment opening it more - quarter to a full turn out and by gosh that did it.

Now it no longer stalls coming to a stop and I also noticed much better performance at higher speeds. It's all one big (fun) learning experience.

[History]

It idles ok but not as good as it did. Have played with the gav adjustment and it makes a difference but I'm still not at the acceleration I was. I'm not able to take it out on the hiway yet so I'm basicly short tracking around my storage buildings, they are 100 feet long and there's two of them, gravel topped, not paved. I checked the jets and passages and all seemed to be fine. I'll keep trying until I find the (ah ha) moment. It's there I just have to keep looking.

[johnbuckley]

If you haven't fiddled with anything else ( eg ignition) it Certainly sounds like it running weak. If your're sure that all the passageways and jets are clear of crud and the fuel flow to carb is good. then the next things I would check for are 1) an air leak at the carb/manifold gasket ( I use a light smear of Blue Hylmoar sealant routinely - not sure if it's available in USA) and 2) the fuel pipe poking through the olive into the carb body too much..( it should not extend more than 1/8 inch beyond the olive, more than an 1/8 and the fluel flow into the strainer gets restricted )

[History]

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Originally Posted by johnbuckley

If you haven't fiddled with anything else ( eg ignition) it Certainly sounds like it running weak. If your're sure that all the passageways and jets are clear of crud and the fuel flow to carb is good. then the next things I would check for are 1) an air leak at the carb/manifold gasket ( I use a light smear of Blue Hylmoar sealant routinely - not sure if it's available in USA) and 2) the fuel pipe poking through the olive into the carb body too much..( it should not extend more than 1/8 inch beyond the olive, more than an 1/8 and the fluel flow into the strainer gets restricted )

I have reused the copper covered gasket a few times removing the carburetor and putting it back on. I'll try some sealant on that. I believe I checked the gas line where it goes in the carburetor and it was sufficient but I will check that again. I think it's good as nothing changed there since the first time.

Thanks for replies and when I figure it out I'll make sure to say what problem I found.

[Brentwood Bob]

Have you recently checked for leaks around the manifold gasket at the block?

[History]

Originally Posted by Brentwood Bob

Have you recently checked for leaks around the manifold gasket at the block?

I did and I checked to make sure those nuts were tight. I don't believe there's a leak there but I will do a few more tests to confirm.

[Bob Bidonde]

The GAV provides gasoline from the float bowl to the idle jet and the cap jet. It does not service the main jet.

Your paperclip cleaning of the GAV may have dislodged some debris that is hindering flow from the idle jet and the cap jet.

Run the engine at high speed and close the choke a few times for one second each. The high vacuum this produces may suck the debris out of the carburetor. However, this will not do any good for the idle jet because the openings in the jet well for gasoline are too small to pass debris.

Another potential problem may be the result of your float adjustment. Adjusting the float off of the engine is a ball park starting point because the angle of the engine in your car may not be 3 degrees. The ideal float height is the point where it is just short of allowing gasoline to drip. Less than this setting may starve the jets. Too low a float height will cause loss of power, and stalling while coming to a stop. Iterate the float height until it is optimum for your Model "A."

One more thing to check. Is the float bowl vented? There is a service bulletin about this.

My last point is that some carburetor gaskets do not fit correctly, and allow a leak of gasoline into the throat. This fit problem result in a vacuum leak that disturbs the flow of gasoline into the jets.

[History]

Bob I believe you're narrowing down on the problem. I believe all passages are open as well as the jets so that leaves the only other thing I changed, float level.

The float bowl is vented through the top of the carb as that is where it leaked when the float was set to high.

My son is home from college and it's his birthday so I won't be working on the A today. I'll let you fellows know what I find or don't.


Thanks again for all replies.

[28tudorsedan]

Originally Posted by jquinlan

After dealing with a leaky zenith carburetor by shimming up the float to the correct level, I was able to stop the carburetor from leaking and the car ran pretty good. However, one new problem that I started having was I would stall when coming to a stop unless I adjusted the idle on the steering column higher.

Last week we took our Model A to the Sweet Home Alabama tour and after mentioning this to a friend there, he asked how much of a turn did I have my gav. I told him I had it just a tad open and he said to experiment opening it more - quarter to a full turn out and by gosh that did it.

Now it no longer stalls coming to a stop and I also noticed much better performance at higher speeds. It's all one big (fun) learning experience.

x2 I also have this issue which is very annoying having to adjust the hand throttle at every stop sign or else I stall might have to back the gav out and give it another try

[Patrick L.]

I have to ask how the passages were cleaned. Since all were not cleaned in the beginning I wondering if there are still some that are not clear.
I suggest staying all the passages with a cleaner such as Deep Creep and then drying with compressed air making sure the spray and air go where they need to go.

[History]

I took the carburetor apart again completely, I was able to see a paper clip exit every passage except the one in the Venturi throat. I was able to spray carb cleaner in that one and had good flow. I’m certain at this point I have no blockage so I adjust the float, allowing more fuel in. I took it for a spin and the same thing, except this time I had fuel leaking out the vent.

Mine is vented in the bottom half of the carb as well as the upper half so I guess it's a mid 30 or after carb.


SO,,,, I took it apart again and adjusted the float level again AND decided to check the plugs. I had already taken them out and cleaned and adjusted the gap to .35. I decided to look at them again and they were black so I cleaned them again, checked gap, checked points gap, cleaned points. Fired it up and she ran like a scalded dog . I’m not sure what the problem was, probably the nasty plugs. I wish I had some information that would be ground breaking but I feel most of you would have figured out before me. I just can’t believe how much better it runs. I did read where Jack Bahm had told someone parade driving would/could foul the plugs and that’s about what Ive been doing.

I appreciate greatly you fellows taking the time to try and help me and I will do my best to pass the effort forward.

[jm29henry]

Bob great pictures for reference I will keep them in my carburetor book

[Wick]

Glad you got it fixed. When you said reused the copper gasket. ... that was 2 red flags in my book.
One thick paper gasket is all you need. Think about it,Henry used paper and just about all engines use a paper gasket.
Wick

[Patrick L.]

Well, as long as you got her going again, good. Maybe a bit 'hotter' plugs would help ?