Weird carb problem

[tazmaniac_37752]

Hello. A friend of mine has a vs800 and between me and him we've tried about everything. He rebuilt the carbs put them back on and now no matter how he sets his float and BTW he's had two different needle valves in it and he found a pin he in the original float so he's replaced it also. Back to the point no matter what he's done fuel still runs out the over flow hole on the rear carb. I'm a purdy good mechanic but this has got me stumped. We are now down to thinking maybe a stuck valve allowing compression back in to the carb and that's causing fuel to run out the over flow any ideas would be great and highly appreciated but plz don't be surprised if we've already tryed the idea you post. Thanks in advance.

[hillsy v2]

There's only one way the carb will spew fuel back out the overflow - and that's because the carb is flooding. Won't have anything to do with sticking valves in the engine.

Either the float is sticking open, the float valve is not sealing or the o-ring for the valve seat is leaking. These bikes have fuel pumps so if there's even the slightest bit of blow by / leakage the carb can flood very quickly.

When you say he's "rebuilt" the carbs - did he remove / replace the float valve seat and ensure a new o-ring was installed?

[Lechy]

I had a similar problem with mine recently. I replaced the needle, seat and O-ring, set the float height but the bastid would still overflow. I inspected the float itself and noticed what looked like a crazy paving pattern on the pontoons, I gave one a gentle squeeze and it fractured along one of the lines. Off down to the local bike shop, found a float with similar sized pontoons but a different yoke, out with the soldering iron and swapped the pontoons. Put it all back together, now it doesn't overflow. I imagine that the thin brass was affected by the crappy new fuels available. Never a problem with the front carb as it utilizes a plastic float. I have noticed quite a few folks are having the same problem on other forums.

[tazmaniac_37752]

He changed float, new needle valve, new seat, and new O- ring.

[Lechy]

Did he adjust the float droop tang? Most floats have 2 adjusting tangs, one for the fuel height shut off and another to set how far the float drops when the bowl empties, if not set correctly the needle can fall too far out of the tube allowing it to tilt over and jam up when the bowl begins to fill with fuel.
You can just make it out in the white box.

[hillsy v2]

He changed float, new needle valve, new seat, and new O- ring.

He should test for leaks with the carb off the bike. With the float and needle out, put a finger over the seat and blow through the fuel line. Shouldn't hear any hiss but if so investigate. Then install the float and needle, and with the carb upside down, blow again. Same deal - shouldn't hear any hiss.

It essentially the same as a toilet cistern valve - its not rocket science.