I'm not familiar with this setup of carburetor

[vybrano]

I'm familiar with setup, where throttle on handlebars-> butterfly -> vacuum -> needle.

But in this carburetor throttle is connected directly to the needle. And butterfly is fully opened all the time. There is a mechanism to control butterfly, but it isn't connected to anything. And it works. But what should it be connected to? Does it matter that it's fully opened all the time?

 

[Texan]

That is for a remote Choke. You would hook up a cable to it and it would be controlled by a mechanism (lever/thumb throttle) on the handlebars.

 

[vybrano]

That is for a remote Choke. You would hook up a cable to it and it would be controlled by a mechanism (lever/thumb throttle) on the handlebars.

So the butterfly would be permanently in open position (like 80% open depending on settings)? And only occasionally (when using choke during starting) would be 100% opened? Do I understand it right?

 

[itsid]

uhm nope, the choke is CLOSED to start (choking the enginge restricting the air flow)
so 100% open is the "running" position
usually the starting position is ~50-60% closed some can close nearly completely though
80% is a bit weak I'd say...
but if that carb is set up that way (and it's not just a semi seized lever action)
then so be it

Whoever added that gigantic petcock lever is riding motorbike in mittens I guess..
uhh what an abomination *yikes*

'sid

 

[vybrano]

Motorcycle starts on first try and Im in tropical country without cold winters. So I will leave it as is, fully opened all the time. Unconnected.

That giant petcock is the reason why I'm taking it apart. It's leaking gas (the core of petcock). Already found new one for $4. And it's exactly the same size. Seems like it's by default this size.

Talking about petcocks, is there any real need to have one (manual or vacuum)? Seems like float bowl in carburator should take care of everything... .

 

[itsid]

uhm.. I'd go for: you want one

while the floats cut of fuel alright if working properly,
they're not preventing an overflow situation reliably
especially not in warm climates.

fuel expands in the bowl when left in the sun, and then is pushed through the overflow
since it also evaporates quickly it can then start cooling the carb body..
remaining fuel contracts opens the float valve fresh fuel comes in and the cycle repeats
which makes the fuel bowl essentially a slow peristaltic pump draining your tank slowly to the ground..
Then the float valve needle wears making the valve leak,
the floats themselves can crack not closing the valve at all etc.etc.etc.

Also: most manual petcocks I've came across also regulate the reserve of the fuel tank
so you wither will not be wanrned when the fuel's almost depleted or you will have an unused amount of fuel degrading in the bottom of your tank...
your's seems to only have one inlet... so that is unlikely an issue for you at all.
still.. petcock good.. closing it when not in use even better

'sid

 

[vybrano]

Great info, thanks!

 

[Whitetrashrocker]

A good little trick.
After a long storage time the gas in the bowl will evaporate and get gummy. This can lead to clogged jets and other issues. To keeping from having to clean out your carb use the petcock to shut off engine before you store it. With engine running, shut off the fuel supply and just let it idle till the carb bowl runs out. The engine dies and your left with a bowl that has the needle open, which won't get goo'd up and a dry bowl.
I've found this to work and I don't have to clean carbs every spring. Just add fresh gas and let her rip.