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Carburetors, Mixers, Fuel Pumps and fuel delivery Discussion about misc. carbs, mixers, fuel pumps, injectors.

Carburetors, Mixers, Fuel Pumps and fuel delivery

Schebler carb help


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  #1  
Old 08-29-2019, 08:11:53 AM
Dustin D Ehli Dustin D Ehli is offline
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Default Schebler carb help

Hey guys I have a large schebler carb that is for a 18-38 Hart Parr.
I have a few questions about fixing it up.
First what size is it, the opening for the manifold flange is 1.75, the air opening is 2 inch??

Second is there anywhere to get a new spring for the air valve, this one seems not good.
The rubber on the air valve seems to be pliable enough to work.

Third, I'm assuming this isn't the correct float?? It had a spring in there to help pull the float open, it was hooked to the needle rod inside when I took it apart.
Thanks for help, info, and parts possibilities.

Dusty.
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  #2  
Old 08-29-2019, 08:48:26 AM
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Default Re: Schebler carb help

Dustin,
Sponsor Dave Reed at Otto Engine Works has new floats. Info on Schebler D carbs can be found on http://www.oldmarineengine.com/
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Old 08-29-2019, 02:18:27 PM
David Hoover David Hoover is offline
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Default Re: Schebler carb help

The air valve spring looks like it’s to long. Might get away with just shortening it.
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Old 08-29-2019, 02:34:18 PM
mmcdonald mmcdonald is offline
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Default Re: Schebler carb help

Float was originally horseshoe shaped cork. New good ones are synthetic foam. That float is out of a TSX or maybe the MA aircraft carb I can't tell exactly. Spring is wrong but tension is all that matters so it's possible it might be modified to work. Don Hoover knows a lot about the Hart Parr carbs. 712-838-4853
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Old 08-29-2019, 03:52:44 PM
Dustin D Ehli Dustin D Ehli is offline
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Default Re: Schebler carb help

Perfect thanks you guys, so what size would this be if opening at flange is 1.75 and air opening is 2 inches
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Old 08-29-2019, 11:36:24 PM
David Hoover David Hoover is offline
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Default Re: Schebler carb help

I took the spring out of my 18-36 and measured it. The carb itself is a dx319. Hope that helps in finding parts. I would check with these guys and see if they have a spring that works. https://www.mcdonaldcarb.com/product_p/x1940.htm . My 18-36 is early and has the dx319. Yours may need a dx320. Apparently some dx304 parts interchange. https://www.smokstak.com/forum/showthread.php?t=125801. https://www.smokstak.com/forum/showthread.php?t=74294
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Old 08-30-2019, 07:23:36 AM
Dustin D Ehli Dustin D Ehli is offline
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Default Re: Schebler carb help

Well my bowl is a dx 320, the air horn is dx 319.

Thanks for the info and pics
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Old 08-30-2019, 11:01:32 AM
mmcdonald mmcdonald is offline
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Default Re: Schebler carb help

That carb is termed "1-3/4". The DX304 is termed "1-1/2". I think the bowl needle cover, load adjustment needle assy, and air valve screw and maybe the float needle retainer nut will work on both. Most other parts are similar but different if I'm remembering correctly. I'll stick with my contact recommendation above.
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Old 09-13-2019, 08:49:01 PM
Dustin D Ehli Dustin D Ehli is offline
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Default Re: Schebler carb help

Put in a float from a d carb, it's very close to the throat but seems like it will work.
It's the composite so if needed I think I can shave it a bit for more clearance.

Another question, what is a good starting point for the air valve spring tension?
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Old 09-13-2019, 09:07:06 PM
J.B. Castagnos J.B. Castagnos is offline
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Default Re: Schebler carb help

The theory of setting these carbs is to use the needle to adjust idle mixture and the air valve to adjust high speed. At idle the air is bypassing the air valve through the slot on the bottom side. You have to adjust idle mixture with the needle, the air valve will have no effect. As you speed up the slot can't provide enough air so the air valve starts to open, it's basically functioning as a choke, richening the mixture. If it's too rich you back off on the spring tension, if lean, increase it. In theory you don't have to move the needle, theory doesn't usually work.
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Old 09-14-2019, 03:14:20 PM
Steve Webre Steve Webre is offline
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Default Re: Schebler carb help

Hey Dustin - Just rebuilt my Schebler for my 18-36 yesterday. Learned quite a bit from talking with JB (above post) and Dave @ Otto.

My carb measured same as yours and Dave called it a 2". He has the proper shaped composite float but to be honest, if yours is working well, I'd leave it. While not original in shape, that brass should last longer than any composite. The originals were cork and had a habit of breaking at the center attachment point.

Ditto on that air spring. Not pretty but will likely work fine. Adjust it as JB said and see what happens.

One item that had me baffled and initiated a "confirmation" call to JB was the observation that the brass needle is heavy enough to shut off the fuel by itself. The float must be adjusted so that it slightly lifts the needle as the level gets low or it will run dry. I had to bend my brass arm just a bit to make it work. Just make sure the fuel level stays below the top of the "jet" in the intake tube. Easy to observe with the carb mounted and plumbed on the engine and the top off. Good luck!
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Old 09-14-2019, 06:17:29 PM
J.B. Castagnos J.B. Castagnos is offline
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Default Re: Schebler carb help

Looks like you solved your issues Steve.
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Old 09-14-2019, 09:24:52 PM
Dustin D Ehli Dustin D Ehli is offline
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Default Re: Schebler carb help

Well I'm talking about the composite float that I got but it's for the D carb, it clears but barely.
I think I can shave it if needed, don't know how I would adjust height cause that float arm seems to be Ridgid, I don't want to break it. It is sorta loose on the pin from wear.
It will be a while until I can get it installed and tested.
I got a new spring for the air valve as well so I have that installed
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Old 09-15-2019, 05:36:39 PM
mmcdonald mmcdonald is offline
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Default Re: Schebler carb help

The needle should have very little movement in the arm. If it's worn, it will act as Steve said. One way to remedy this is to incrementally remove material from the float arm where the retaining nut goes. This will allow you to "take up some slack". Just do a little at a time with a mill or file until the needle still moves freely but you have very little up and down movement in the arm. Assuming you have substantial wear and you adjust the float arm so that it picks up the needle you are also raising the fuel level in the bowl by setting the float higher. Before I removed material from the arm I would try a new needle as the "ball" portion will not be worn then if necessary remove material as stated above. If you remove material with a used needle you may have to shim the retaining nut if/when you install a new needle. If you don't mind shimming later it doesn't matter. If you have a green float you can remove material without compromising it. I do not know about other kinds. We make a float for the large Hart Parr carb that is very similar to the JD style but the float is larger where it straddles the casting. If the float is "hitting" the casting when moving up and down you are going to have an overflow problem at some point. Good luck.
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Old 09-15-2019, 09:10:44 PM
Dustin D Ehli Dustin D Ehli is offline
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Default Re: Schebler carb help

Thanks, I got the float from you guys, was t aware that you had a bigger one. It's the green one.
I don't remember how much play there is in the needle, I was talking about the arm pivot, it's worn so there is side to side play.
So maybe I should grind the float thinner, or get the correct one, and maybe replace needle also.
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Old 09-16-2019, 03:36:54 PM
mmcdonald mmcdonald is offline
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Default Re: Schebler carb help

Perhaps I misconstrued what was said about float adjustment. If you're dealing with wear at the pivot pin and are using a new pin then the arm will need to be repaired. We would typically drill and put a sleeve in to remove the play. Alternatively, you could fill the hole up and re-drill it but that method would leave more room for error in putting the pin hole back in the right place/geometry. If you have the ability to put the hole back in the same place and plane, filling it up and re-drilling would be the simplest without buying or making a sleeve. The hole for the pin must be back in the exact same spot and angles within reasonable tolerances. If you get it off by much, the main problem is that your needle may not be in alignment with the seat. The needle might be at an angle instead of straight if that makes sense thus causing it not to seal.
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