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Chemically cleaning brass - gently

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Kiwi Bloke19/01/2021 23:34:03
693 forum posts
1 photos

Hi Folks,

Because our electrical power supply is not 100% reliable, we have a small generator, for occasional use. Every time it's needed, it won't start until I've whipped off the carb and cleaned greenish corrosion(?) off and out of the brass(?) jets. This is in spite of draining the carb's float chamber after each use. The deposits are hard, and don't dissolve in sprayed-on carb cleaner, which is why I suspect corrosion rather than gum deposition. Typically, it's months between uses. It's a four-stroke engine. It's said that Kiwi petrol is low-quality stuff, but I don't know whether it's more prone to form gum and varnish or corrosion on standing: perhaps it contains more water than desirable.

Two questions. Does 'fuel stabilizer' prevent this sort of problem - if it's corrosion rather than 'varnish' build-up? How would one clean the jets safely and within say one hour (and yes, I know better than to poke around with wire, etc.)?

Michael Gilligan20/01/2021 00:06:04
20289 forum posts
1064 photos

Green corrosion indicates Copper Oxide ... a common problem with some greases used on microscopes, but that shouldn’t be relevant to your jets !

My guess would be water in the fuel.



Had a quick look round, and found this very interesting document, which may be helpful:


Edited By Michael Gilligan on 20/01/2021 00:06:27

not done it yet20/01/2021 05:50:31
6880 forum posts
20 photos

Hi KB,

If your fuel contains any appreciable amount of ethanol (most do, these days), that is likely your problem. There are fuels without ethanol for small engines or stabilising additives. Some additives work and some are likely snake oil.

Better to avoid the problem than forever cleaning jets. Donnyboy73, on youtube, likely gives some reasonable advice.

Russell Eberhardt20/01/2021 08:39:19
2751 forum posts
86 photos

If, as Michael suggests, it is copper oxide you could try using household ammonia solution to clean it.


Dave Wootton20/01/2021 08:43:12
316 forum posts
66 photos


I used to run until recently a couple of classic bikes and was plagued with fuel problems caused by the ethanol in petrol attracting moisture. A friend recommended Sta-Bil fuel stabiliser and it does work really well I could leave a bike over the winter and it would start no problem. I did used to run the float chambers empty before putting them away, but still found green corrosion and white deposits in the carbs, the Sta-Bil stopped all that. I got mine via ebay, but i think it's readily available.


pgk pgk20/01/2021 08:52:42
2594 forum posts
293 photos

It might be worth considering 'Aspen' fuel - supposedly burns cleaner and likely less hydroscopic but more expensive.

With my assorted mowers/machines and genny I try to remember to run them up every month when hardly used. I haven't had to use the genny in anger for a couple of years but nice to know that it'll start and run (on it's electric starter) 'cos wife can never manage a pull start if I'm away.

Isn't ethanol in petrol supposed to rot some of the plastics used? I've had to change a few fuel lines to more robust stuff.


SillyOldDuffer20/01/2021 09:57:13
8863 forum posts
1995 photos

Just a thought, but is the petrol old, perhaps kept in a can next to the generator? Ethanol won't damage brass, but Ethanol absorbs water which does. If it's an older engine, also possible the ethanol is attacking a plastic, and the product of that is corrosive.

Petrol might be watery out of the pump if the supply chain is wonky. Most likely suspect is an elderly roadside tank - they collect muck have to be changed periodically. Petrol taken from the bottom of an nearly empty tank can be filthy. Is there an oil refinery in New Zealand? In my part of the UK petrol has few opportunities for being mucked up because it comes from a local refinery. If New Zealand petrol is imported, the chance of contamination en-route across the Pacific to Kiwi's generator is much higher.

The ethanol in clean petrol gradually absorbs moisture from the air even if the can is closed because water molecules are smaller than petrol molecules and diffuse through the seal.

At first water absorbed by ethanol in petrol goes harmlessly into solution. But as more is absorbed, water drops out of solution and sinks to the bottom of the tank. There's a distinct risk that the end of a fuel can left standing will almost pure water, definitely bad for engines!. Also that simply draining the engine will leave a lot of water behind. I suggest:

  • Use new petrol, and minimise storage time. (Perhaps monthly burn aging generator petrol in your car and refill the generator. )
  • Before pouring the end of a can into the engine make sure it's not watery.
  • Don't drain the carb, instead run the engine once every few weeks to warm it through and stop wet fuel settling.
  • If draining for long-term storage, rinse the engine thoroughly and try hard to exclude water by wrapping etc,


Kiwi Bloke21/01/2021 08:23:59
693 forum posts
1 photos

I guess that the greenish 'corrosion' might be a form of verdigris - a term covering several possible Cu compounds - but I doubt that it's due to a copper oxide, which should be reddish or black, not greenish. If atmospheric oxygen is contributory, however, in the relatively complex corrosion chemistry, perhaps it's a mistake to drain the carb between uses. If corrosion is because of the petrol's water content, perhaps one should drain. I don't think I'll be successful in obtaining ethanol-free petrol here - but I will certainly try, it sounds like a very good idea.

Anyone know how to safely remove verdigris?

I'm sure the advice to run the engine more frequently is likely to be successful. It's what I've been trying to remember to do, but...

Michael Gilligan21/01/2021 08:58:10
20289 forum posts
1064 photos

I stand corrected blush

The green corrosion product on greased microscope slide-ways is more likely this: **LINK**



But you might understand my confusion :

Edited By Michael Gilligan on 21/01/2021 08:59:50

Russell Eberhardt21/01/2021 15:26:41
2751 forum posts
86 photos
Posted by Kiwi Bloke on 21/01/2021 08:23:59:

Anyone know how to safely remove verdigris?

Yes, clock cleaning fluid which is a mixture of water, ammonia, oleic acid (olive oil will do), and a touch of acetone. Best used in an ultrasonic bath to get into small holes such as pivot holes in clock plates but should work on brass jets.


Michael Cox 121/01/2021 15:54:54
550 forum posts
27 photos

Nearly all copper and zinc corrosion product will be soluble in household amminia solution. This will rapidly dissolve the corrosion products. Unfortunately household ammonia solution, which used to be a common cleaning agent during most of the 20 th century, is now quite difficult to find although it is readily available via ebay. If you use this wash with water afterwards and then rinse with alcohol (methalated spirit, denatured alcohol) and leave to dry.

Bazyle21/01/2021 15:56:15
6379 forum posts
222 photos

If you know you are going to remove and clean the jet how about removing it after use and storing it in the dry until needed?

Or make a new one out of stainless. (after checking a bit of the stainless doesn't corrode in that environment) It doesn't need to be hard to machine 18-8 just cutlery steel, of perhaps bronze or nickel would do.

Bit more hassle but fit a new carb of the plastic variety from a lawnmower. This is presumably a device kept for its utility not as an horistorical item like an old Lister Startomatic.

Kiwi Bloke22/01/2021 09:37:09
693 forum posts
1 photos

Nearly all copper and zinc corrosion product will be soluble in household amminia solution.

I think that ammonia-containing preparations are used to remove copper fouling in gun barrels. This suggests that the elemental metal is attacked by ammonia. My school chemistry has corroded almost entirely away, so can't remember what the chemistry is. It doesn't sound risk-free for jet cleaning if ammonia attacks Cu.

One is warned not to use ammonia-based cleaners in stainless-steel gun barrels - why not? What's the chemistry here?

If you know you are going to remove and clean the jet how about removing it after use and storing it in the dry until needed?

Well, there two jets and an emulsion tube, and it's a pain to dismantle, and I'm lazy. Prevention would be better, but your suggestion would certainly save time, and I can't fault the logic...

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