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Old 01-02-2021, 01:38 PM   #1
JayJay
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Default Zenith Carb Questions

All - I'm into my Zenith-2 carb and have a couple of questions I'm hoping you more experienced folks can help me with. Car started and ran OK before I began, but the carb is really rusty and gnarly looking, and there was a lot of crud in the glass sediment bowl, so I figured a good cleaning and rebuild was time well spent.

1. Throttle shaft bore tolerance. My throttle shaft measures 0.280"+, nominal is 9/32" (0.281"). Bore in the carb casting measures (gage pin) 0.287", and it feels a bit sloppy. The oversized shaft available from the vendors is 19/64" (0.297"), so I'm a long way from that.

I can see maybe 0.002"-0.003" for a slip fit, but given that this is a somewhat hostile environment under the hood, is 0.006" unreasonable? I could find some brass tubing, overbore the casting and ream to fit I suppose, but I'm more interested in how far off the mark these numbers are.

2. Main mixture seat (bottom of the choke rod). Mine is cast into the carburetor body. Looks a bit cruddy. How does one clean this, given that it can't be removed? I found a package of wooden BBQ skewers with a long tapered point that I used (with a bunch of brake cleaner) to rotate in the seat, and got quite a bit of crud out. Is that good enough (repeated often until clean), or is there some other magic? This is a relatively large hole, compared to others, and adjustable, so I suppose you live with what you can get, but I'm open to other suggestions. I will be replacing the needle with the new one I got in the rebuild kit.

Thanks, all. Happy New Year, and stay healthy.

JayJay
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Last edited by JayJay; 01-02-2021 at 02:26 PM.
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Old 01-02-2021, 02:18 PM   #2
Brentwood Bob
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Default Re: Zenith Carb Questions

Tom Endy discusses cleaning the zenith.
You will find his write up on the Santa Anita A's Webb site.
The wear is excessive in my opinion. 19/64 is .29678".
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Old 01-02-2021, 02:21 PM   #3
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Default Re: Zenith Carb Questions

https://www.santaanitaas.org/tom-endys-tech-articles/

BobX2. Scroll down to fuel. There is an article by Tom Endy on cleaning Zenith passageways with a paper clip.
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Old 01-02-2021, 02:27 PM   #4
JayJay
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Default Re: Zenith Carb Questions

Quote:
Originally Posted by Brentwood Bob View Post
Tom Endy discusses cleaning the zenith.
You will find his write up on the Santa Anita A's Webb site.
The wear is excessive in my opinion. 19/64 is .29678".

Thanks for seeing my typo, Bob. Was looking at the calculator and clearly had a disengagement.


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Old 01-02-2021, 08:12 PM   #5
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Default Re: Zenith Carb Questions

To really get the carburetor clean inside and out you will need to soak it in carburetor cleaner. You can purchase a 1 gallon can/kit from most any auto parts store. The can has a metal basket inside that you can put the smaller bits and pieces in to soak them too. The cans now a days are not labeled as carburetor cleaner but as parts cleaner. You will need to repaint your carburetor after soaking it as the paint will be removed.
Scrub it with soap and water afterwards and blow out the passages with compressed air. I like to heat my carbs with a propane torch right after washing and blowing them out to reduce rust flash over and to get the passages nice and dry.
Don't be in too much of a rush to use the needle valve that comes in the kit if the tip on yours is still in good shape. I've never been terribly impressed with the fit of the new ones.
The kit works really well for cleaning up other parts just be sure to wear nitrile gloves as it will take the oils out of your skin pretty darn quick.
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Old 01-03-2021, 12:52 AM   #6
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Default Re: Zenith Carb Questions

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Good tips on cleaning carburetors Dave. Chemical cleaning is best. Please don't bead blast carburetors to clean them like a lot of "rebuilders" do. I realize this thread is about Zeniths that will be painted but IMO bead blasting ruins the finish on Tillotson and Marvel Schebler carb bodies and brass and plated parts in all carburetors.
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Old 01-03-2021, 09:50 AM   #7
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Default Re: Zenith Carb Questions

And those tiny beads can get into tiny holes and stay there until ??
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Old 01-03-2021, 10:17 AM   #8
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Default Re: Zenith Carb Questions

I glass bead the cast iron carb bodies all the time. All that is needed is a good cleaning and air pressure to blow the passages out when done. Brass plated parts may be one thing, but the brass bodied carbs sure do look nice after a bead blast and buff! Soaking type carb cleaners, when they work, may get rid of the crud but not the rust.
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Old 01-03-2021, 10:45 AM   #9
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Default Re: Zenith Carb Questions

My go-to carb cleaner is Pine Sol.
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Old 01-03-2021, 11:37 AM   #10
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Default Re: Zenith Carb Questions

For bushing choke and throttle shafts, thin wall brass tubing is available at hobby shops, it's used in model airplanes.
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Old 01-03-2021, 12:50 PM   #11
Ruth
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Default Re: Zenith Carb Questions

Quote:
Originally Posted by redmodelt View Post
I glass bead the cast iron carb bodies all the time. All that is needed is a good cleaning and air pressure to blow the passages out when done. Brass plated parts may be one thing, but the brass bodied carbs sure do look nice after a bead blast and buff! Soaking type carb cleaners, when they work, may get rid of the crud but not the rust.
As I mentioned, you can paint Zeniths. I was referring to Tilloson and Marvel carb bodies. Bead blasting ruins the finish on pot metal castings, throttle and choke plate and shafts.

No thanks, I will stay away from blasting.
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