Recently did the valves and refreshed the remote vacuuam lines.
When Inremoved the front line there was a small amount of fuel in it.
The rear one had none.
Occasionally when I start my bike it backfires, could this be linked to fuel in the remote vac line ?
Any suggestions ?
Fuel In Remote Vac Line
Fuel In Remote Vac Line
South Coast
New South Wales
Australia
New South Wales
Australia
Re: Fuel In Remote Vac Line
It is actually nothing to worry about and is totally normal.
to answer why doesn't the vacuum pull the fuel out of the line, first we have to go over a few misconceptions about vacuum and how things react.
I will try to keep thing simple, though as someone who was involved with vacuum technology for my entire working career the technical bit sometimes slips out.....
So the first thing that has to be covered is the common misconception that vacuum pulls things. This is not the case, the higher pressure outside the evacuated area pushes.
Back when I used to teach folks how to use their new mass spectrometers and this came up all the time. One way to think of it is vacuum, by definition, is the absence of everything or an empty space....aka nothing.
So if vacuum is pulling, the nothing is doing work (In this case moving something). This is not possible or if you can figure out how to do it you would run the planet.
With this in mind, this is what is happening. When the piston is on the intake stroke (when it creates the vacuum signal) it also has fuel in the mix.
As per the gas laws, they expand to fill the entire area evenly. Which means there will be a small amount of air\fuel mix in that hose.
When the piston passes the port and closes it off, it is still below atm pressure. So the next time it passes on the exhaust stroke you have high pressure (comparably) and since the tube is closed ended and not at complete vacuum, what is in the tube gets pushed all the way to the end.
The next intake stroke, the slightly higher pressure comes out. Yes a small amount of the fuel will also come out but some of it is under the pressure pocket and remains in the tube.
If it bothers you, angle the line up so the fuel can run out once the engine has stopped or just not worry about it
to answer why doesn't the vacuum pull the fuel out of the line, first we have to go over a few misconceptions about vacuum and how things react.
I will try to keep thing simple, though as someone who was involved with vacuum technology for my entire working career the technical bit sometimes slips out.....
So the first thing that has to be covered is the common misconception that vacuum pulls things. This is not the case, the higher pressure outside the evacuated area pushes.
Back when I used to teach folks how to use their new mass spectrometers and this came up all the time. One way to think of it is vacuum, by definition, is the absence of everything or an empty space....aka nothing.
So if vacuum is pulling, the nothing is doing work (In this case moving something). This is not possible or if you can figure out how to do it you would run the planet.
With this in mind, this is what is happening. When the piston is on the intake stroke (when it creates the vacuum signal) it also has fuel in the mix.
As per the gas laws, they expand to fill the entire area evenly. Which means there will be a small amount of air\fuel mix in that hose.
When the piston passes the port and closes it off, it is still below atm pressure. So the next time it passes on the exhaust stroke you have high pressure (comparably) and since the tube is closed ended and not at complete vacuum, what is in the tube gets pushed all the way to the end.
The next intake stroke, the slightly higher pressure comes out. Yes a small amount of the fuel will also come out but some of it is under the pressure pocket and remains in the tube.
If it bothers you, angle the line up so the fuel can run out once the engine has stopped or just not worry about it
Loud pipes don't save lives, knowing how to ride your bike will save your life.
Re: Fuel In Remote Vac Line
Thanks for the reply.
I get the concept however,
Why is there no fuel in the rear vac line.
Both lines rest in the valley between the cylinders at the same height.
Granted the pick up points are at different heights though.
Any thoughts on the odd backfire On starting, everything on the bike performs well under wide conditions from 3000 Rpm in 6th gear through to WOT in all gears .
No rhyme to the backfire, can happen if bike is hot or cold but not all the time.
Weird!
I get the concept however,
Why is there no fuel in the rear vac line.
Both lines rest in the valley between the cylinders at the same height.
Granted the pick up points are at different heights though.
Any thoughts on the odd backfire On starting, everything on the bike performs well under wide conditions from 3000 Rpm in 6th gear through to WOT in all gears .
No rhyme to the backfire, can happen if bike is hot or cold but not all the time.
Weird!
South Coast
New South Wales
Australia
New South Wales
Australia
Re: Fuel In Remote Vac Line
Without 1ATM pushing down on us at sea level we would float away 
==============================Enter the Darkside
Re: Fuel In Remote Vac Line
If the front one (presumably for carb balacing and plugged) dips below the level of the takeoff then fuel could gather - compared to rear pop takeoff that operates the fuel tap curves directly upwards and wouldn't allow fuel vapour to condense & settle - at a guess.kenmoore wrote: ↑Sat Apr 27, 2019 12:24 pm Thanks for the reply.
I get the concept however,
Why is there no fuel in the rear vac line.
Both lines rest in the valley between the cylinders at the same height.
Granted the pick up points are at different heights though.
Any thoughts on the odd backfire On starting, everything on the bike performs well under wide conditions from 3000 Rpm in 6th gear through to WOT in all gears .
No rhyme to the backfire, can happen if bike is hot or cold but not all the time.
Weird!
re backfire - air leak somewhere in intake / exhaust / vacuum hoses or plugs.
It may be that your whole purpose in life is simply to serve as a warning to others.
VTR Firestorm and other bikes t-shirts
VTR Firestorm and other bikes t-shirtsRe: Fuel In Remote Vac Line
Wicky got it..... it is the angle of the lines.
The front one usually ends up pointing down so fuel can be trapped while the rear line angles up so any fuel left in the line will run down into the cylinder.
As for the backfire, tough to call over the net. This bike does use a wasted spark ignition (the plug fires every time the piston comes up to TDC)
So you are getting extra fuel that is firing off on the exhaust stroke I would think at this point.
I would start by checking the starter valves in the choke system. they might be worn and one could be flowing more than the other one.
The front one usually ends up pointing down so fuel can be trapped while the rear line angles up so any fuel left in the line will run down into the cylinder.
As for the backfire, tough to call over the net. This bike does use a wasted spark ignition (the plug fires every time the piston comes up to TDC)
So you are getting extra fuel that is firing off on the exhaust stroke I would think at this point.
I would start by checking the starter valves in the choke system. they might be worn and one could be flowing more than the other one.
Loud pipes don't save lives, knowing how to ride your bike will save your life.
Re: Fuel In Remote Vac Line
Sounds like a carb cough, they all do it, don't worry.
It's not falling off, it's an upgrade opportunity.
Re: Fuel In Remote Vac Line
Thanks for all the replies,
Plenty to think about.
Definitely a backfire, and only intermittently on starting.
Very rarely get a carb fart .
No biggy, thought it might be a common occurrence or that someone else had had the same happen to them.
Plenty to think about.
Definitely a backfire, and only intermittently on starting.
Very rarely get a carb fart .
No biggy, thought it might be a common occurrence or that someone else had had the same happen to them.
South Coast
New South Wales
Australia
New South Wales
Australia