Intermittent overflow

[Big T]

I've been chasing an overflow issue on my 78 1000

A carb will suddenly overflow for 1-2 seconds, sometimes it's #2, sometimes #4,etc.

When they're not *@%^$*@%^$*@%^$*@%^$ing, they'll slowly drip

I pull and dismantle the offending carb, say #2, find nothing, spray all the parts, reassemble and #4 will start overflowing ( or some other)

It will be fine for a while, then start the cycle again

I've tested the floats, polished the needles and seats, triple checked float heights, cleaned and flushed the fuel tank, swapped needles, don't know what else to check

Could it be

Debris in the tank? I never find any in the float bowl
The springs on the float needles failing? I check that they move freely, could they just be worn out after 47 years?
Any ideas?

[Nessism]

Sounds like your fuel level is high. Right on the ragged edge of overflowing.

Why, is the next question. Float valves wear, and don't seal perfectly. Needle springs get weak. Floats age, and get heavy.

Start with performing the "clear tube" fuel level test. Adjust the float height, to the extent it helps. I've had carbs where no amount of float height adjustment changes the fuel level. This is when you start pulling out hair.

If you can't adjust out the high fuel level, my default is to install new float valves, then go from there. I have a pile of china floats, but can't say they have helped the situation much.

[Sandy]

Did check that they're not binding on the float bowl? Give carbs a shake after installing the bowl and you should have a nice crisp rattle from the floats.

[chuck hahn]

I would check the float arent canted and rubbing on the gaskets and that the overflow tube isnt cracked at the seam. Put a line on the overflow nipple and fill the bowl with water. Put finger over the tube and blow in the line and if theres any crack youll see bubbles. Polish clean and flux and solder the tubes.
I have a bunch of VM26 bowls and floats if you need any