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Refurbing Carbs - In what condition should you replace the jets

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exvalvesetdabbler:
You need to examine the top  oraface of those emulsion tubes to see if  corrosion or wear has enlarged the hole. If it has look forward to some black spark plugs. For the needles, can you feel the machining marks with your thumb nail or are they well polished.

What about the float valves, is there noticeable ridge worn on the conical tip.

The jets should be ok so long as you don't open them up by poking steel wire through them.

Main jets I put string through and rub them up/down the taught string.
Pilot jet - copper wire out of mains cable flex.


Regards
Dave

deltarider:
I can testify the CB500/550 carb brassware goes a looong way. The last time I had it out, I couldn't detect any wear. To me that's no wonder. This may sound blasphemous to some, but the CB500/550 engine is nothing more than 4 125cc lawnmower engines that happen to share one and the same crankshaft. No less than 4 carbs for 500cc displacement!
On my odo: 142.000km. Let's say the average fuel consumption has been 1 liter for every 17.5km. So the total amount of fuel consumed has been some 8000 liters, which is 2000 per carb.
Below the pics I took. Now you might think you see a very little wear on the floats needles. There isn't. I have felt with my nail a dozen times if I could detect even the beginning of a ridge. Well, there isn't. What you see is merely optical. If I cannot detect any wear and have no symptoms either, I see no reason to fix what ain't broken.
Our brothers across the pond have a different attitude. They reason: if aftermarket parts are on the market, it means there is a demand and there is problem to be solved. And as always, they are happy to buy stuff.
Now, it could well be that other motorcycles do need replacement of the brassware - I have once heard a mechanic complain about some model Goldwing - ours just happen to prove very durable. Enjoy!

Oddjob:
My 1971 CB500 has 423000 kms on it, my 1972 one has 268000 kms. Both are still using the same carbs it came with from new. No jets have been replaced on either. Although the 71 one had the main jets changed when it was being raced but back to the old ones when I stopped. They’ve occasionally leaked from the overflow but never when leaded petrol was available. Both banks have been apart a few times for maintenance and painting.

If you can’t find a float bowl in a few weeks Neil let me know. I have a bank of carbs which I’ve broken for spares lying about. However my medical condition isn’t the best at the moment so I’d prefer not to have to rummage in the garage if I can help it.

Where in the UK are you Neil? I think I’ve asked that before for some reason. Maybe alter your profile to include it?

Sesman:
I would have no qualms about hoking out a blocked jet with proprietary probes. Just don’t be aggressive and use a sensibility sized probe. The jets are made of brass, not cheese. Stubbornly blocked pilot jets can cleared by heating via a gas flame and probing with a wire to clear the ash. I know cos I’ve done it successfully.

For example, clearing a #40 jet with a #38 probe is highly unlikely to change the jet diameter by a demonstrable amount - think cross sectional area and percentage change. It’s highly unlikely the CSA change through cleaning could approach a CSA enlargement that would be equivalent to a change in jet size!

deltarider:
This is what I use: stranded copper wire.

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