SOHC.co.uk Forums > Anorak's Corner
Thoughts on a fix for CB500/550 CB400F Main Jet Sealing on Corroded carbs.
AshimotoK0:
I have been thinking ages for a decent fix for the tubular 'tower' part of the casting that the main jet fits into on the CB500 627B carbs and 400/4 carbs. You often get otherwise lovely condition carbs with the end of that alloy 'tube' moth eaten with corrosion, caused, I assume, by water in the fuel. (see attatched image showing what I mean) If I could find an aluminium filled epoxy that is resistant to modern fuels, that may be an option. I may try this stuff filled with ultra-fine aluminium powder. https://uk.rs-online.com/web/p/potting-compounds/1991468/
I also thought of a really thin washer of soft Viton that would seal between the top face of the main jet and the bottom face of the needle jet, that's assuming that there is a seal between the needle jet and the body. If not then how about an extra 'O' ring in the needle jet itself. The Viton washer would have to be really thin and the float height may need adjusting slightly to compensate for its thickness. A more radical option might be to solder the main jet to the needle jet but still fit the extra 'O' ring.
Building up with alloy low melting point solder is a 'no-no', as the carb alloy is lowish melting point too. I did think or slightly reaming out the alloy tower (or whatever it's called) and making main jets that are slightly oversize in diameter, withsuitably larger 'O' ring but there is not much 'meat' at all on that tower tube, even prior to it getting corroded.
Any more thoughts? I think Gerben in Holland just rejects any carb bodies with this kind of damage.
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This is the problem .. Otherwise decent condition inside the carb apart from corroded main jet mounting 'tower'
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Tomb:
--- Quote from: AshimotoK0 on May 08, 2020, 05:56:37 AM ---If I could find an aluminium filled epoxy that is resistant to modern fuels, that may be an option. I may try this stuff filled with ultra-fine aluminium powder. https://uk.rs-online.com/web/p/potting-compounds/1991468/
--- End quote ---
I just seal them back in with Epple 33, its petrol proof (among other things proof)
https://www.ebay.co.uk/itm/1-Tube-95g-Epple-33-Dichtstoff-100g-13-16-Sealant-epple33-/173126481685?hash=item284f247715
https://euro-industry.com/main.php?index=details&cat=299&prod=23206784&lang=en
https://shop.seipp-gmbh.de/products/epple-33
I've sealed all sorts of petrol leaks over the years with this stuff, 9 years ago I sealed carb leaks on a Yamaha Mikuni carb on a daily rider, still going well, toured all over Europe with it using E10 fuels. I also use it on a race bike that burns NOS and VP Import High octane race fuel which doesn't touch the sealant,
AshimotoK0:
--- Quote from: Tomb on May 08, 2020, 08:30:13 AM ---
--- Quote from: AshimotoK0 on May 08, 2020, 05:56:37 AM ---If I could find an aluminium filled epoxy that is resistant to modern fuels, that may be an option. I may try this stuff filled with ultra-fine aluminium powder. https://uk.rs-online.com/web/p/potting-compounds/1991468/
--- End quote ---
I just seal them back in with Epple 33, its petrol proof (among other things proof)
https://www.ebay.co.uk/itm/1-Tube-95g-Epple-33-Dichtstoff-100g-13-16-Sealant-epple33-/173126481685?hash=item284f247715
https://euro-industry.com/main.php?index=details&cat=299&prod=23206784&lang=en
https://shop.seipp-gmbh.de/products/epple-33
I've sealed all sorts of petrol leaks over the years with this stuff, 9 years ago I sealed carb leaks on a Yamaha Mikuni carb on a daily rider, still going well, toured all over Europe with it using E10 fuels. I also use it on a race bike that burns NOS and VP Import High octane race fuel which doesn't touch the sealant,
--- End quote ---
That stuff looks good ..well worth a try.
Bryanj:
Ash, does Devcon still exist and is it petrol proof? Type F for ally if memory serves
Tomb:
The Epple 33 is the only sealant I have ever found that seals petrol and other fuels and solvents.
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