starting without the gas tank

[tatu]

It's not about letting go. It's about controlling the level, by controlling the flow, while the fuel is flowing. Not about stopping the flow and holding the pressure, it's about controlling the volume in the float bowl accurately. Three times the pressure will flow more and will effect the resulting float level somewhat.

An empty tank, the fuel level is maybe 6 inches above the needle valve? Maybe eight? Full tank maybe 14 - 16 inches? Put the tank up two or three feet higher and you are increasing the flow through the needle valve, the needle then needs to close farther to get the right flow, the floats must float higher to do this, and as the fuel level gets higher, the engine runs richer.

No, you are not increasing the flow, if you put the tank up three or four feet, you are putting the tank up three or four feet. increasing the flow can only come about by increasing the amount of fuel in the tank which will make it heavier which is where your 'head comes from then your flow will increase. ((and or increase the diameter of the pipe (but then only increases flow not head)) but this is irrelevant in this case)

The floats are there in the carb in order to maintain a level of fuel in relation to the venturi and that absolutely must not be allowed to change.
Once a float leve is set its set, rightly or wrongly it will not chang during the operation of the engine, unless of course the fuel supply is removed then it stops when the bowl runs below a level that the venture cannot maintain a flow, then it runs weak.

[tatu]

The fuel level change is virtually nothing. If it weren't then every time you pushed your bike through the twisties it would run like crap.

Head pressure is height times density times gravity. If you pull a bit of G in a bend it would have the same effect as putting your test tank on your roof.

It would not, it would have the same effect as adding a bit more fuel.

[tkent02]

The fuel level change is virtually nothing. If it weren't then every time you pushed your bike through the twisties it would run like crap.

No, becuse the same G load that increases the weight of the fuel also increases the weight of the fuel in the bowl, increasing the bouyancy of the float.

[tatu]

No, becuse the same G load that increases the weight of the fuel also increases the weight of the fuel in the bowl, increasing the bouyancy of the float.

No, floats do that, float, in the twisty bits g force increases downwards thus making them less floaty. but it doesn't mater because they are more floaty than we can pull in g s'

[hampshirehog]

No, becuse the same G load that increases the weight of the fuel also increases the weight of the fuel in the bowl, increasing the bouyancy of the float.

The float also gets heavier by the same percentage so the buoyancy stays the same.

[tkent02]

The float also gets heavier by the same percentage so the buoyancy stays the same.

Hmm, have to think about this, but the change from G loading, if any would be minuscule, and short lived.

Meanwhile the change from having the tank up too high is much much more drastic, and stays in effect the whole time.

[hampshirehog]

Hmm, have to think about this, but the change from G loading, if any would be minuscule, and short lived.

Meanwhile the change from having the tank up too high is much much more drastic, and stays in effect the whole time.

You're right, it wouldn't be much but if you're on full bore you're drinking a lot of fuel.

As long as your tank wasn't at a silly height, enough to force the float valve open when it should be closed then it won't effect how the bike runs when.

Don't forget that the height of the head of liquid is measured at the top of the liquid. So a full tank exerts 2 or 3 times the pressure than a nearly empty tank and yet the bike runs the same all the time (rusty sediment excepted ).

The float valve opening and closing controls the fuel level height - not the pressure.

[Wuts11]

I can't ignore this one. Basic hydraulics, water pressure at the bottom of a column increases 1PSI for every 2.2 Ft. of height. ( fuel will be slightly different ) It is the same with a 10FT.diameter pipe or a 1/4" fuel line. Try giving yourself an enema and lift the water bottle up and down, you will feel like you are going to BLOW! I made this mistake once ( not with the enema )working on my GS had fuel coming out everywhere, lowered remote tank to normal tank elevation, all was well.

[tkent02]

I can't ignore this one. Basic hydraulics, water pressure at the bottom of a column increases 1PSI for every 2.2 Ft. of height. ( fuel will be slightly different ) It is the same with a 10FT.diameter pipe or a 1/4" fuel line. Try giving yourself an enema and lift the water bottle up and down, you will feel like you are going to BLOW! I made this mistake once ( not with the enema )working on my GS had fuel coming out everywhere, lowered remote tank to normal tank elevation, all was well.

Yeh, fill a hose with water, hold the pressure with your thumb as your buddy takes the other end up the stairs to the roof. No water is being added, but the pressure sure is being increased.

Or think about how the ancient Egyptian water levels worked, A big body of water connected by a pipe to a small one, but both of them always go to the same level. If the big body put down more pressure you could pump water uphill without using any energy.

[tatu]

I can't ignore this one. Basic hydraulics, water pressure at the bottom of a column increases 1PSI for every 2.2 Ft. of height. ( fuel will be slightly different ) It is the same with a 10FT.diameter pipe or a 1/4" fuel line. Try giving yourself an enema and lift the water bottle up and down, you will feel like you are going to BLOW! I made this mistake once ( not with the enema )working on my GS had fuel coming out everywhere, lowered remote tank to normal tank elevation, all was well.

I can't ignore this one. Basic hydraulics, water pressure at the bottom of a column increases 1PSI for every 2.2 Ft. of height. ( fuel will be slightly different ) It is the same with a 10FT.diameter pipe or a 1/4" fuel line. Try giving yourself an enema and lift the water bottle up and down, you will feel like you are going to BLOW! I made this mistake once ( not with the enema )working on my GS had fuel coming out everywhere, lowered remote tank to normal tank elevation, all was well.

Made it want to blow a slight exaggeration there, taking your 1 psi every 2.2 feet you would lift it, what 3 feet higher than standard, what would that be 1.5 psi? hardly nuclear I'd say, and as I say again in this case insignificant.
I was going to leave this because I'm simply repeating myself and getting nowhere.
Normal tank elevation indeedy. Bah! Nice happy story

Yeh, fill a hose with water, hold the pressure with your thumb as your buddy takes the other end up the stairs to the roof. No water is being added, but the pressure sure is being increased.

Or think about how the ancient Egyptian water levels worked, A big body of water connected by a pipe to a small one, but both of them always go to the same level. If the big body put down more pressure you could pump water uphill without using any energy.

I'm very aware of fluids finding their lowest levels, and again, a pound of fuel is a pound of fuel the only variable in this is the volume in the tube, and again, its insignificant in this case. As I said oh so long ago.
As I said I was going to leave it but I just wanted to put it to bed so that we are all clear, that you will not change anything by lifting the fuel supply.
I've had enough, I am right on this and if you disagree then you are wrong.
Simple.
It's not a damn dam with a pensacola or whatever, inlet, or a pond in the sky or scotch mist settling in the glen its a tank of gas, and you can be damn sure those needle vlvs will hold back more than a lousy 40lbs of fuel. A lawn mower tank perched on your roof will not make an iota of difference to the carbs.

[tatu]

Today, having a little time on my hands, I though I would take this to a full conclusion, this is what we did, Richard, Londonboards came round and gave a hand. He says he'd not read this thread.
Anyway on to the experiment.
I dug out an old GS1000 fuel tank because it would be the biggest one I had.
I topped it to the brim with fuel and it took a gnats over 19 litres, that was 42 pounds.



This is the set up with a pressure gauge at the bike end and at about the standard level. The gauge was 0 - 15 psi (2 bar) (because it was the smallest reading one I could get) But for this it was good enough.



The bike started and ran normally and the gauge was at zero which I was surprised at because I did expect it to at least register something because it had forty + pounds above it.

Here we raised the tank about four feet above normal, actually way more than we would use in a working workshop environment but anyway did it anyway, no leaks, no strange running just idled and revved fine. Actually the gauge is about five vertical feet below the bottom of the fuel tank, a foot lower than the carbs



The bike started, idled, and revved normally, no leaks.



So really this is the place I should have stopped as it proves what I contend that in this case its of no significant difference to us in this case.

But of course I didn't.. We stuck a wheelie bin on top of my shed roof and perched the still full tank on top of that which put it at fifteen feet from the floor, thirteen feet above the carbs,






This is what the gauge said. About 1.5 psi. The bike started, idled and revved normally no leaks. I did have a problem wit a sticky float valve early on in the experiment on carb no 3 but that was cleared up by tapping the offending bowl with a hammer after that no leaks whatsoever. I have not touched the bike since middle November last year.



I hope this helps clear this up.
The only thing that I wish I'd'v done was drain off ten or fifteen litres and seen what the gauge said but I didn't think of it at the time.

[hampshirehog]

I don't believe that for one moment.

Richard came round and there's no photograph of a half drunk bottle of beer?

You're making it up.........

PS new members will really think this is the nuthouse. After all, what normal person puts their wheelie bin on the shed roof.

[tatu]

A bit cold to be messing about with beer, we did think about sticking the tank up on the roof of my house but I didn't fancy the idea of going up the slope of the roof carrying forty pounds of petrol. Richard offered to do it but still didn't think it was a good plan.

[Agemax]

firstly, thanks Wally for assuming it was me causing "trouble" again.what are you trying to say?

secondly, i have argued before about this stupid theory and i have always maintained that a small 1 or 2 litre tank, a few feet above "normal" fuel tank level, or even a full GS gas tank for that matter, will have NO EFFECT WHATSOEVER on the carbs when balancing or idle screw setting etc. etc.

forget all the physics theories and hydro pump scenarios, they dont mean nothing when it comes to actually doing it!

The temporary tank works just fine, has always worked just fine for me, and always will.

Tatu, i think your experiment just about proves everybody else wrong and hopefully all the budding physicists will zip up now and just get on with it.

However, i am disappointed at not seeing Richard balancing on a wheely bin, perched precariously on your house roof, with a full GS tank of gas balanced on his head and a bottle of beer in his hand.
I think you should repeat the experiment accordingly, maybe on a day when a lightning strike is imminent (purely for some great photographic effects, of course)

[Griffyn]

PS new members will really think this is the nuthouse. After all, what normal person puts their wheelie bin on the shed roof.

I don't tend to like the sort of people who WOULDN'T put a wheelie bin on top of their shed roof with 40 pounds of flammable liquid on it when the reward for doing so is to conclusively end an internet argument.

If only the oil debate were this easy to solve.