Getting ready for synchronizing the carbs

[JTGS850GL]

Here's my rendition of an auxiliary gas tank:









Still need to add a cutoff valve and fuel lines but you get the idea.

[chuck hahn]

There are so many ways to make a gravity tank. I have seen some way cool things from soda bottles to now PVC pipe. Mans gotta do what his wallet says...which is usually " hey dude..your broke so get to inventing something so we can hook this biitch up".

[GSJohnny]

I'm in the same boat.

Here is my stab at it.



re-purposed an old oil bottle.

Went to harbor freight and picked up some brass air fittings and on/off valve.

Also grabbed a cheap clear fuel filter that I had laying around.


The fittings go from a 1/4 opening (fuel filter) to roughly a 3/8 hose barb to accommodate bike fuel line.

Flows good... fuel-tight when valve is closed.

$5 bucks well spent I say.


~GSJohnny

[Steve]

The fittings go from a 1/4 opening (fuel filter) to roughly a 3/8 hose barb to accommodate bike fuel line. ... $5 bucks well spent I say.

Might need to spend another couple of bucks.

Your stock fuel line will never fit on a 3/8" hose barb.

Stock line is 7mm, which is smaller than 5/16". If you use a 5/16" hose barb, you will be able to stretch the fuel line onto it, hope it doesn't damage it.

.

[Andrew Vanis]

Below is my alternate/temporary tank setup.

The coolant reservoir was ~$9 at the auto parts store. I got the one with the metal frame. Has 5/16 outlets and comes with vinyl tubing and clamps that will work as fuel line for carb synch (for longer use, use real fuel hose).

The 5/16 shut-off if from a small engine (lawnmower) repair shop ~$5. Also came with spring clamps.

I hang it from the handle bars for engine work and can take it for 15 mile rides like an actual temp tank bungied to the frame like in this picture. (tank is being redone)

[Steve]

Just remember that, when using your temp tank, don't raise it any higher than the gas would normally be in the main gas tank.

Hydraulic pressure increases with head height, so the higher you raise the tank, the harder it is for the float valves in the carbs to control the flow.

.

[Agemax]

Just remember that, when using your temp tank, don't raise it any higher than the gas would normally be in the main gas tank.

Hydraulic pressure increases with head height, so the higher you raise the tank, the harder it is for the float valves in the carbs to control the flow.

.

where does the hydraulic pressure come from?????? it is atmospheric pressure acting on the fuel, which will be the same if the temp. tank is 2 inches above the carbs or 2 feet!

[Steve]

Actually, the pressure comes from the weight of the fluid, not the difference in air pressure.

Connect a pressure meter to your tank, hold the meter a couple of inches below the gas level, note the reading. Raise the tank (or lower the meter), note the difference. It is substantial enough to make a difference, especially if questionable float valves are in the picture.

.

[Agemax]

Actually, the pressure comes from the weight of the fluid, not the difference in air pressure.

Connect a pressure meter to your tank, hold the meter a couple of inches below the gas level, note the reading. Raise the tank (or lower the meter), note the difference. It is substantial enough to make a difference, especially if questionable float valves are in the picture.

.

but its not hydraulic! and those temp tanks hold way less than a stock GS tank

[Steve]

but its not hydraulic! and those temp tanks hold way less than a stock GS tank

Would you be more comfortable calling it "head pressure"?

Gasoline (petrol) quantity has nothing to do with it. You could raise a half-pint container up six feet and overpower the float valves. Or, ... you could have a hundred-gallon tank at normal tank height and have no problems at all.

.

[Agemax]

yeah ok Steve.......if you say so..

[JTGS850GL]

Steve is right on this one. The amount of fluid above a specified point determines the pressure exerted by that fluid. Think of it as diving down into a pool of water. The deeper you go the greater the pressure exerted by the water above you. The air pressure exerted on top of the water is the same. In the case of the gas tank, the coulomb of fluid is equivalent to the depth of the water. The more fluid above the point you're measuring, the greater the "depth" and the higher the pressure that is exerted by that fluid. It’s all about the weight of the fluid and not the air pressing down on the fluid from above. Here's a pic that might clear it up:

[Agemax]

i was just saying it is fluid under atmospheric pressure, it is NOT hydraulic!

[Andrew Vanis]

i was just saying it is fluid under atmospheric pressure, it is NOT hydraulic!

not quite...

This explanation uses the term fluid but is also relevant for gas just the pressure differences are much less in gas due to its density - just think of the fluid as a gas that is heavier than the surrounding atmospheric gas (so it actually stays in the container)

What one is concerned with is the height difference between the top of the fluid/gas and the point of where it exists. I like to think of it as "how much stuff is above where it comes out. You will notice the higher you raise the top (by raising the tank or by filling it up more) the more pressure you get at the bottom.

This relative difference is independent of the path the hose takes between the top of the fluid and the exit. (please ignore the special case where the exit hose goes above the top of fluid in the reservoir)

This is also independent of the volume at any certain height - a large reservoir on top and a small hose on bottom or large reservoir on bottom with a hole in it and a tall hose that is filled going into this large reservoir.

[JayWB]

The weight of the fluid in the column going from the tank to the carburetors is the issue. A 6 inch column of fuel weighs considerably less than a 6 FOOT column of fuel.