Float-chamber ventilation valve

[sujitroy]

I've been trying to resolve my hot starting issues. Someone, I think Tony Hart, mentioned to look at the float-chamber ventilation valves and its operation
I have an old set of carbs. in front of me and this is what I've observed. In the normal case, the valve is meant to open one vent passage and close another depending on the throttle. However, If you adjust the throttle to maintain, 800 rpm (BW35), both vent passages are open. I recall when starting the Stag, the throttle should be closed, (I used to pump on the accelerator).
I read the description in the ROM and it's Greek to me what it really does and will it help my hot staring issue and can some please explain what is the purpose of it?

I have carb. setup B
Sujit

[Phil S]

the pump on the throttle is to remove the loading on the choke cable while it is pulled out. su and stromburg carbs don't have a fuel pump in the carb like a webber

[trunt]

That valve is very unlikely to cause idle or running problems unless one or the other is blocked. They are simply a vent for the float chamber which needs to be open to atmosphere. Therefore you can remove all 4 pipes to the carb and see if that helps.

In normal operation the float chamber is at or about atmospheric pressure. Don’t imagine that because the fuel pump has pressure then the float chamber is pressurised in any way - it’s not.

When your throttle is being used it ports the vent to the air cleaner which sweeps up the fumes and they go into the engine to be burned. In Federals when you turn the engine off The fumes would escape from the air filter box and they didn’t want that! so when the throttle is on the stops they are ported to the carbon canister to be filtered by the carbon.

OK there are some shenanigans going on with that “anti Run-on valve” which was needed because of the timing on a federal. Thats for another post! If anyone is interested.

Terry

[RNF]

Bringing this not so old thread back.
I had the Stag out for a drive and ran into an issue with fuel just pissing through the overflow down the front of the engine the other day. I took the carbs apart to see if debris had clogged a needle valve and saw nothing. Then I noticed that one float chamber vent valve (LHD driver side carb) was open all the time and one seemed to be operating correctly with the throttle. The throttle stop is just barely touching, so there is no movement to be gained by backing the screw out as there will be no idle adjustment. The valve operates freely, however as you can see with the way the linkage is set up, there is no way for the valve to close. The ZS manual talks about set up of the valve, but with the way the linkage is currently set up, there is no way to close that drivers side (LHD) valve. What am I missing here?
Capture.JPG

[dasadrew]

This sketch from Klaus SChlueter may help to clarify some details on the operation:
K1600_Bild 5 +Details - Kopie - Kopie - Kopie.JPG

[mike@thenook]

I periodically spray carb cleaner into the vent pipes on both carbs and this so far has both eliminated and prevented any problems of fuel overflowing in such a way. I think maybe they stick sometimes but thecarb cleaner sorts that out.