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Mikuni Carburettor Question (s)

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Mikuni Carburettor Question (s)

Stripping a very gunged-up Mikuni carburettor, off a neglected 133cc Yahamaha RZR 2-stroke. Despite its sorry state, its a welcome relief from the concurrent issues with the "snakepit" 1986 Aisan on my Daihatsu car, because its comparatively SIMPLE.

One thing's bothering me though. I want to put the needle to soak in carb cleaner, but I can't get the rubber/plastic (?) depth stop (?) off, and I don't really want to expose it to carb cleaner long term.

I also can't offhand see how its supposed to work. There are rings on the top of the needle that a little C-washer locates in. I THINK they are supposed to provide an adjustable depth stop for tuning, BUT in fact the depth seems to be fixed by the rubber/plastic thing, which won't move, so it looks like they only affect the spring loading on the needle.

Pictures hopefully tell the story.

A : Dirty carburettor


B: Driving the float pin out. I embedded the carb (which is an awkward shape to hold) in potters clay in a plastic bag for hammering (my idea). I'd guess "silly putty", wet cornflour, (hippy mis-spent youth givaway) or concrete would also work. It was still stubborn, though, and I ended up using a spring loaded centre-punch (not my idea, but a very good one).


C: Disassembled; Parts 1-5 L>R on the bottom row are the needle slider assembly.


D: The needle assembly


E Needle C-washer


I've removed the C-washer, but the rubber thing seems fixed on the needle.


(1) Is the rubber thing supposed to be removable? (I THINK it must be, because otherwise the depth isn't adjustable, but it does seem pretty firmly stuck.)

(2) If I can't remove it, is it likely to be OK if soaked in (3M) carb cleaner?

(3) Does the needle in fact have an adjustable depth stop?

PS. I had to empty a small whisky bottle to soak the parts in, so its possible things will be clearer after I sober up a bit.

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