Pilot screw

So, I'd noticed that the pilot screw on my LH carb looked oddly green (the colour brass goes when it oxidises) so I tried to take it out for a clean just now...and the four castellations, if that's the right word, forming the cross-head in it, all just came off when I tried to turn it. 

In the words of Eddie Izzard: quod the fu*k?

I adjusted the screws about ten months ago and they were fine then. The other one looks fine. All I can think of in explanation is that maybe I've been having a miniscule leak from the coolant hose union just beside it which has caused it to corrode. There is some evidence of dried coolant in that area...

To get this out, can anyone think of an ingenious way that doesn't involve taking the carbs out? That said, I was planning on swapping my main jets fairly soon so I could just wait till then. And if I do, what's the safest way to extract the bastard without risking damaging the carbs or getting swarf anywhere I don't want it?

If it's likely to be a huge faff then perhaps I should clean and prepare the carbs off my old CB and just swap them over. The only thing about that is that bike had done 145,000 miles so some bits like the throttle linkage and valves might have a bit of wear...how easy would they be to swap?

Sorry, but I can't think of any easy way.

TBH having another set of carbs on hand so you can swap them out sounds like quite an easy solution!

You can then try and drill out the brass screw.... or you could try a really small screw extractor.  Once you've got them out you'll be able to soak bits of it in penetrating oil, which will only make it easier and less likely to brake things.

I'm definitely going to use my old carbs. I opened one up yesterday and it all looks pristine even after nearly 150,000 miles! First time I've ever opened these or any carbs and actually it was a lot simpler and easier than I expected. Fear of the unknown etc...

Obviously I'll use all the removable parts from the newer carbs though, transplanted into the old carb assembly. I've ordered a pair of new pilot screws. Will be fun cleaning it all out and setting it up myself. As discussed in another thread I'll be putting in #125 main jets and raising the jet needle with an extra shim washer because my engine's running a tad lean with my Fuel exhaust. 

As for removing the stuck pilot screw, another suggestion I've had is to saw a slot in the screw. This does involve cutting into the carb body a bit though so I'd have to be very careful but it sounds feasible. 

I hope to do the job this weekend but will be sure to document my progress.

So apart from replacing all gaskets and o-rings and transferring the jets and other internal bits from the newer carbs to the old ones, is there anything else that it might be wise to check/replace/lube/otherwise attend to, bearing in mind the large mileage the old carbs have done?

I can't quite remember what it is called (needle jet holder?) buy anything associated with the needle can wear and might be better on the newer bike.

Oh yes, good point. I'll be swapping the needle jet and jet needle, but do you perhaps mean the float needle valve and float valve seat? I'd be using the valve from the new bike but the seat seems to be part of the carb...I'll see if it's removable. It's not listed as a part in the fiche and Haynes doesn't mention how to remove it or list removing it as part of the overhaul; but it does say 'Check the tip of the float valve and the valve seat. If either has grooves or scratches in it, or is in any way worn, they must be renewed as a set.'

By the way, another bit of Lings-derived humour here: guess how much a complete set of new carbs is....

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ONE THOUSAND SEVEN HUNDRED AND THIRTY-TWO POUNDS, FIFTY-ONE PENCE.

Is that all? I assume that's before they've added VAT

Hahaha. I swear next time I have an hour to waste I'm going to go on there and see how much a complete bike in bits would cost.

A bit of online research suggests that the float valve seat is not replaceable. Don't know why Haynes talks about replacing them 'as a set' then. It sounds like some people have successfully burnished wear away with fine emery paper, but I hope I don't have to do that. I think the tip of the needle valve is rubber so hopefully the brass seat won't be worn. I know these things are incredibly sensitive so if it does look worn I may have to change plan and get the stuck pilot screw out of the newer carbs after all. Looking at it, I don't think a bit of hacksawing into the carb body around the screw (as a necessary by-product of sawing into the screw itself) should be harmful as long as I'm not over-zealous.

Only four years on, I've realised what almost certainly caused my pilot screws to seize.

I had had an issue with the cooling system (https://cb500.forumotion.com/t2839-another-puzzling-cooling-issue) where there were no visible leaks but the level was consistently a little bit low and the engine was taking a bit longer to cool down than usual/generally running a bit hot, which after replacing almost all components in the cooling system turned out to be solved by replacing the carburettor heater hoses.

Well, when I had my carbs off the bike the other day, I realised just how close these hose unions are to the pilot screw. My guess is that the tiny leak (maybe even just in the form of escaping coolant vapour?!) over time caused corrosion of the brass of the pilot screws, visible as the green deposits on them and manifested by them being completely seized in the carbs and disintegrating when I tried to remove them.

Check those carburettor heater hoses!!