How to prevent cast iron carburetor flash rust/internal


I've recently acquired 3 new (to me) tractors that have all sat for a considerable amount of time. As part of the repairs I plan on going through the carbs and soaking them, along with the carb for the tractor I've owned for a while. The way I do this is to spray down any stuck parts w/ PB blaster, disassemble the carb, and then I use an ultrasonic cleaner to clean the parts. The concoction I have in the cleaner is a mix of white vinegar (to get after rust), ATF, and acetone. It works GREAT at cleaning the parts. The issue I'm running into is after removing the parts, rinsing them off, drying, and starting reassembly, the parts start to flash rust within a few minutes. While I plan to paint the exterior of the carburetor, my concern is that rust forming on the inside will plug up jets and prevent the needle from seating properly. I can try and coat the inside and passages with oil but its difficult to ensure that it gets everywhere and I'm unsure how long it will realistically last. So far the flash rusting has happened on two carbs I've attempted to clean in this manner.

So, what can I do to stop the flash rust or what am I doing incorrectly to cause it? I've seen where you can "season" cast iron pans and such but I'm not sure if that's advisable, let alone possible with a carburetor.

Anybody have any experience or wisdom in this area?


Also, if it matters, the tractors are a 1948 JD A, 1949 JD B, 1950 Farmall H, and a 1962 JD 1010. Might be a year or two off on some but that's ball park.
Submerging the clean parts in a container of diesel fuel or similar liquid until you are ready to assemble seems like it would work.
I lightly blast all my carbs in my blast
cabinet. Clean with spray gumout and fine
wires. Blow out and reassemble. Then I
spray them with clear laquer. Works pretty
good at stalling rust and resists gas.
I keep my cast iron carbs full of gas.
I took one carb apart and while sitting on my workbench exposed
to the air waiting for a carb rebuild kit to arrive it rusted
after 3 days.

I ordered a new aftermarket carb off Amazon for $40 that looked
like my 73 year old zenith carb off my Farmall C.

It worked perfectly after I got it adjusted.

Check out Amazon for a generic aftermarket carb. Less hastle.
Nothing is going to rust if you blow the parts off dry with
air. Then u can spry then with brake clean and blow them
off again. Rust will not happen.
I did two JD carbs about four years ago and they still in storage with no problems. I soaked in Purple Power then hot-water rinsed. I primed and
painted right away and stored them in plastic ziplock bags with a packet of silica jell. That tiny amount of flash rust will just wipe off and will
not cause a clogging issue. Or you could just wipe some oil on the insides after the paint is dry. I clean gears, shafts, bearings and even sheet
metal parts in PP. Internal parts get oiled, painted parts get a coat of self-etching primer. Left overnight t will take off paint.
Part of the problem is the vinegar which has to be removed completely and then some sort of oil/grease coating put on the carb or yes it will start to rust fast. Vinegar being an acid helps start the rusting pretty fast
Like Old said you have to get the vinegar off. Or it will continue to rust from the acid in it. Wash them just like you have been and then dry well. The bit of flash rust you worry about is not a problem if you wipe it off with a dry rag then coat parts with an oil.Setting in Diesel fuel would stall your rust problem while working on them and would give them a coating of a very light oil when out to work on so the rust would not advance. OR of there is no rust on the carbs you are working on at that moment, just omit the vinegar for those ones. As for that light flashing of rust all cast iron will do that, if cleaned down to the raw iron, and not dried immediately. Then a coat of oil wiped on it. I washed an Engine block with a steam cleaner one time to get the grime off from it and by the time I was done and dried it off the cylinder holes were rusting like you describe. I just wiped them dry and oiled was no problem that way and the ruse wiped off from the bores with the rag as I dried them. IF you get them cleaned down to the raw cast iron it is pretty hard to prevent that unless you can have a very dry arid climate to work in.
Agreed. After thorough cleaning I'd give the parts a shot of WD40. By design it displaces water and leaves a very light oil film behind.
(quoted from post at 13:35:33 12/11/23) Nothing is going to rust if you blow the parts off dry with
air. Then u can spry then with brake clean and blow them
off again. Rust will not happen.
his is true, as long as the relative humidity stays below 70%, bare clean steel will not rust. Everything will develop a film of salt, dust and oil in a matter of seconds after it is cleaned, even in a clean room. If the air is moist, the film will be corrosive.

A dip in phosphoric acid will leave an iron phosphate coating that will hold enough oil to prevent rust pretty well. Soak for a few minutes, rinse well, final rinse with distilled or RO water and blow dry. For better protection spray with WD-40, Boelube, CorrosionX Aviation (from good to better) after applying the phosphate.

The best price on phosphoric acid for a quick and dirty iron phosphate coating appears to be milkstone remover. Milkstone cleaner is very similar to Bonderite C-IC 33, which I have liked for decades. Both have a degreaser and a similar concentration of phosphoric acid. Since I found Showcrop's posts about Milkstone cleaner I think I will change to the less expensive material. The main differences here are that Bonderite costs twice as much, is harder to find and isn't orange.

Allprep is similar in strength to Milkstone remover, and they have a decent video which I just found and watched. For room temperature they say to dilute it 1:10 with distilled water.[/url]

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