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Old 04-13-2012, 03:22 PM   #1
cuda
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Default Zenith carb rebuild

I took apart my Zenith carb on my '29 and saw that the fuel valve looks different than what's in my kit. In the pic, the one on the right is what was in there already, the left one is the new one. Is one of these styles better than the other?

Also, is it really necessary to drill out the passage plugs? They never leaked and I'm inclined to leave them alone.
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Old 04-13-2012, 04:01 PM   #2
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Default Re: Zenith carb rebuild

I like Tom Endy's method to rebuild. http://modelabasics.com/carb%20basics%202.htm Click on Restoration Tips by Tom Endy. He recommends not to re-drill.
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Old 04-13-2012, 04:18 PM   #3
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Default Re: Zenith carb rebuild

The valve on the left is the original style, the one on the right is a newer style with a Viton (think synthetic) tip rather than metal and is supposed to be better. In my opinion, the best one is the one that does not leak.
If the carb is clean and you can use compressed air and/or the paper clip method to test the passages, there is no need to drill the plugs.
The key to a good rebuild is testing the jets and getting them re-jetted if necessary to flow the correct amount of fuel. Any rebuild that does not include flow-testing is at best just a good cleaning.
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Old 04-13-2012, 04:51 PM   #4
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Default Re: Zenith carb rebuild

There is an article in the September/October 2011 Restorer, page 28, that shows how to check that the passageways are open with a paper clip.

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Old 04-13-2012, 06:49 PM   #5
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Default Re: Zenith carb rebuild

Thanks guys. I will certainly use the paper clip method. For flow testing, can I just have an elevated water supply flow water into a jet connected by hose/tube of some sort, let the water flow by gravity, collect the water exiting the jet into a measuring container, and see how much water is collected over time? This seems like the easiest/cheapest way to do it. I saw some setups had pumps in them, but I don't get what that's for.
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Old 04-13-2012, 07:25 PM   #6
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Default Re: Zenith carb rebuild

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Folks,
Let's get practical about this. Why flow testing?Who's gonna' build flow testing pump, tubes, guages, timers, etc, in order to get certain amounts, in certain time spans? Quantities you do get, does that REALLY mean anything?
If jet sizes are what specifications call for, you're set to go!
Paper clip probing won't tell you any more about a passage than blowing in them to see if they're open. Either way WON'T tell you if there's scaly passage deposits that might flake off sometime and PLUG a jet! You don't have to be a Werner Von Braun to clean & overhaul a ZENITH carb. If you're worried about scaly passages, then CAREFULLY drill out the plugs & CAREFULLY run the proper size bit to clean them. Run the bit with a HAND CHUCK, again, VERY CAREFULLY! Bill W.
( If I catch too much hell for the above statements, I can easily un-plug my KOMPUTATOR! )
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Old 04-13-2012, 07:39 PM   #7
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Default Re: Zenith carb rebuild

Bill, I thought about most of that myself, but it seemed everybody said you had to flow test.
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Old 04-13-2012, 08:07 PM   #8
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Default Re: Zenith carb rebuild

Quote:
Originally Posted by cuda View Post
Bill, I thought about most of that myself, but it seemed everybody said you had to flow test.
cuda,
Folks seem to delight in over complicating a VERY simple & basic car, why? I don't know!! Maybe it makes what they do seem more impressive, as if they've just tuned a DUESENBERG, or just ground the valves on a V-24 FERRARI. (That's their 9.7 litter screamer! ) Bill W.
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Old 04-13-2012, 07:43 PM   #9
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Default Re: Zenith carb rebuild

Willie,

No BS on flowing the jets! There are a lot of repop jets out there, and they don't
flow correctly. I did a Zenith and it did not run right( I new it had repop jets), changed
to originals and it ran fine!
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Old 04-13-2012, 07:54 PM   #10
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Default Re: Zenith carb rebuild

Quote:
Originally Posted by d.j. moordigian View Post
Willie,

No BS on flowing the jets! There are a lot of repop jets out there, and they don't
flow correctly. I did a Zenith and it did not run right( I new it had repop jets), changed
to originals and it ran fine!
DJ,
Was the re-pop's hole sizes different? Or was it phyco-symatic?? (don't tell Berndette that I don't know how to spell it!) wILLY dOE.
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Old 04-13-2012, 08:02 PM   #11
d.j. moordigian
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Default Re: Zenith carb rebuild

Let me regress a bit....IF it run crappy after the rebuild, I would suspect the jets!
This is going on the thought that all the passages are clear and clean, and not
suspect.

If
it runs good after the rebuild....we dodged that bullet.

Now, who's going to catch hell?
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Old 04-13-2012, 08:07 PM   #12
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Default Re: Zenith carb rebuild

Willie....."The Shrink is in".....and needs money to pay off those loans!

UHH.....you need help?
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Old 04-13-2012, 08:32 PM   #13
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Default Re: Zenith carb rebuild

Couldn't it be sufficient to just check the hole sizes with ends of the drill bits? If the next bigger size won't fit and the next smaller size does, wouldn't that make it close enough?
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Old 04-13-2012, 08:47 PM   #14
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Default Re: Zenith carb rebuild

Quote:
Originally Posted by cuda View Post
Couldn't it be sufficient to just check the hole sizes with ends of the drill bits? If the next bigger size won't fit and the next smaller size does, wouldn't that make it close enough?
YUP! Chief, my dad and Guru of Model A stuff, rebuilt carbs down in the woods of Oklahoma, NO electricity, I worked a tire pump with a pointy pipe in the hose while Chief blew out the passages & jets. He cleaned the carbs with Lye soap & water in a cast iron pot hanging on a hook in the fireplace. He "built" Model A's to sell, so we could EAT. He was associated with Buddy Boggs, the county's un-authorized Model A Heaven, and Bill Ogan, the hometown Authorized Ford Dealer. I've got a "million" Model A stories, if I could remember them all! Bill W.
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Last edited by BILL WILLIAMSON; 04-13-2012 at 09:05 PM. Reason: Fun Stuff
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Old 04-13-2012, 08:36 PM   #15
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Default Re: Zenith carb rebuild

Mr. Cuda:

You are getting some very conflicting advice here. I don't claim to be an expert, but my experience with rebuilding Zenith carburetors has taught me that three very important factors have to be achieved if you expect to have a properly functioning Zenith.

1. The passage ways must be open.

2. The jets must be flow tested and resized to the original spec. Most repos and many originals have been molested over the years are way off the mark. For instance, if the comp jet flows more than the cap jet the GAV circuit is useless.

3. The float valve must be properly set, and it should be able to hold the set level for a reasonable amount of time.


To return to your original question and your photo, the float valve on the left is a repo of the original type. It has a steel needle valve inside. The one on the left is also a repo known as a gross ball valve. it has a small ball and a large ball inside. I have seen a number of these fail. It may have something to do with the gas here in California. What happens is the small ball sticks in the seat, probably because there is not enough weight to dislodge it from the goo in the gas.

You can get a viton tip valve from Bratton for about $10. I have had very good luck with these. It is important that the valve not only shuts off at the proper set level, but holds that level for a reasonable time. The viton tip valve seems to do that well.

Go to www.ocmafc.com It is the web site of the Orange County Model A Ford Club. On the menu at left scroll to "tech articles" and click. It will bring up a new menu. At the top is my name, click on it. It will bring up a menu of tech articles I have written. Scroll down to the bottom. There is two Zenith articles listed. One is the one another barner in this string mentioned. Click on these. You can down load them, print them out, and use them as you see fit. There is a photo of a flow tester, a float lever setting jig, and a photo of a Bratton viton tip float valve.

Flow testers are not hard to build. There are several people in my club who have constructed one. The fountain pump is so you can recycle the water and work indoors without flooding the place. Flow testing and resizing jets is a time consuming tedious job, but it is very important if you want to have a good functioning Zenith.

Good luck with your project.

Tom Endy
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Old 04-13-2012, 09:02 PM   #16
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Default Re: Zenith carb rebuild

I am inclined to agree with Bill in reguards to flow testing jets !!!! I do not believe Zenith and Holley flow tested their jets when building the carburetors new for Ford.
Frankly, in rebuilding carburetors the past 30 years I have never flow tested jets, of course, I use original jets, check the orfis for damage, check size of jet openings using the smooth end of torch tip cleaner that I have mic for different sizes by thousands: example Idle Jet .021 , Comp. Jet for early double venturi .018 , etc., check passages ways to be sure they are not plugged.

Many of the new available jets are junk !!!

This is just my opinion and I am sure others will have comments or disagree with me, so be it.

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Old 04-13-2012, 09:06 PM   #17
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Default Re: Zenith carb rebuild

Thanks everyone for the comments on flows. Didn't know it was that controversial I may just use that origninal float valve, mostly because I already own a rebuild kit that has it. Though if I'm really better off with the viton style, I don't mind ordering one.

Is it necessary to paint the castings? Mine don't appear to be and they look ok, especially for a 30yr old restoration. I was planning on just hitting them with some carb cleaner to clean them up.
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Old 04-13-2012, 09:19 PM   #18
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Default Re: Zenith carb rebuild

When you say newer kits aren't that great, this kit has been lying in a box for several years, though I don't know exactly how old it is. Any idea if this one is decent one or not? I will at a minimum check the hole sizes of the jets
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Old 04-13-2012, 10:12 PM   #19
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Default Re: Zenith carb rebuild

I put a new kit in my original zenith and it kept overflowing until replaced the new jets and needle valve with the cleaned up originals.

The new kits are no good. At least the one I had wasn't.
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Old 04-13-2012, 10:38 PM   #20
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Default Re: Zenith carb rebuild

It is difficult to determine if the kit is all OK. The three problems items I have found in the past:

1. The idle jet pickup tube is thick walled instead of thin walled like a original; also the orfice is not dished and often times to large of an opening, Most original idle jet opening is .021 or .022.

2. The idle air screw is often too short and does not close off the air mixture completly; runs ot of threads before seating.

3. The needle on the GAV often runs out of threads before seating which allows more fuel to flow to the secondary well which effects the idle jet and the cap jet. Compare the threads to a original needle.

I have used the junk idle jets, by breaking off the idle end and flating out the pickup tube to form a handle; use these to screw into the other jet openings to block off so I can check the passages for being open and not plugged.

Using the smallest glass beads, I bead blast the upper and lower housings; the small beads will pass thru the passageways, if not I drill out the plug for proper cleaning. The other benifit of glass beads it eliminates rust in the jet threads so when jets are installed you know if the jet will hold. Have found this condition on very rusty housings which just had to be thrown away.

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