Can someone tell me if the fuel flow is still controlled by vacuum when the stock petcock is in the reserve position? 05 FLHT carbed.
Thanks in advance for any help.

 

Yes it is.

 

Without vacuum, fuel will not flow at all

 

unless you gut it and install a blanking plate.

 

What about at full throttle (no vacuum) ?

 

Takes much less vacuum to open the petcock valve than it does to close the VOES. Turning over at starter speed will create enough vacuum to open the petcock.

Think about - if there was "no vacuum" at WOT, fuel wouldn't leave the carburetor.....

 

Maybe very little vacuum on the air filter side of the carburetor, but there is some vacuum on the intake manifold side of the carb.


There does not need to be vacuum in the inlet for fuel to flow from the carburetor.

The venturi effect creates a low pressure at the carburetor throat, which draws the fuel out.

The venturi also causes a drop in the air temperature at the throat of the carb, which can cause carb icing under certain conditions (the reason aircraft piston engines have a provision for heating the inlet air).

I always liked the idea of the vacuum shutoff petcock (I never had a bike that had one), but they have caused a generation of riders to not learn a good old school motorcycling habit...

Turn the fuel valve off when the engine is shut off.

Sorry for wandering off topic...

 

WRT "What about at full throttle (no vacuum) ?" I was referring to the vac petcock, not the carb. Sorry about the confusion.

 

There is always vacuum, in order for there to be no vacuum, the intake pressure would have to be greater or equal to ambient air pressure. In other words turbo/super charged.

 

It is a safety device. First line no mater what position manual fuel valve is in.

Modern Harleys have it as a bank angle sensor that kill the fuel pump. It's main purpose is it shuts off fuel if motor is off.

As Harley get few miles on them, the needle and seat can leak. This overflows the carb and in the right position can fill the cylinder and crankcase with fuel . Also spill over around bike.

Needle and seat can leak and you not even know it if idle can take care of it. However, in a day or week, it can destroy a bike.

The modern bank angle turns the motor off in a fall. Vacuum lacks this ability, so on a carb Harley, practicing the use off switch on bar may be handy.

Sure this post if not already is is for the tin man to say use his manual valve and that I am a safety nut. So be it.

Really, not. Just saying what is for and at $25 repair for number two, that should last about 50 years. It's stupid to remove it.
It's just too easy to get distracted and forget to shut it off. My last carb bike had a decal on shield to turn it. I still more then once had to reach down and cut it on.