mauricejota7604
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- Victoria Australia
Thanks Stefan I will screw the connector down on the carb' body tonight!! 
M.
M.
valve clearance closing up
- Thread starter mauricejota7604
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tom3c75
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- Location
- Cape Town South Africa
Laverdalothar
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- Location
- Germany
Tom, to which part of the oil-cooler does the feed connect and to which the return? right, the lowest part is connected to the feed. Why? because only that setup fills the cooler completely.
I never understood why people make the setup like in your pics... Connect the tube that comes from the pet-cock with the LOWER inlet and the one that points to the rear shall be connected also with the LOWER inlet of the center carb.
You fill a system bubble free only if you feed it from the ground. See your old chemistry lessons... What would happen if you exchange the feed from 6 to 7 on the below pic? right, the blue area wouldn't fill completely with water, the inner tube wouldn't be cooled correctly etc...:
I never understood why people make the setup like in your pics... Connect the tube that comes from the pet-cock with the LOWER inlet and the one that points to the rear shall be connected also with the LOWER inlet of the center carb.
You fill a system bubble free only if you feed it from the ground. See your old chemistry lessons... What would happen if you exchange the feed from 6 to 7 on the below pic? right, the blue area wouldn't fill completely with water, the inner tube wouldn't be cooled correctly etc...:
B
bob
Guest
Lothar, sorry to disagree but I doubt if connecting the petcock to the lower or upper feed union into the carb will make any difference whatsoever. There is a head of fuel in the fuel tank which gravity will feed via an inlet union into the chamber above the needle valve regardless of the relative position of the inlet unions.
Bear in mind you're always going to feed into a Dellorto float chamber from above no matter which spigot you choose to use!
The oil cooler analogy is not a good one. An oil cooler is fed from a sump. The oil pump feeds into the lowest point simply so that oil is allowed to drain back down through the lowest point to the sump when the engine is switched off . If it was fed from the top you'd be left with a cooler full of cold oil when you switched the engine on again.
Of course this will depend on where your oil cooler outlet feeds to. On the 500 it feeds to the cylinder head.
Bear in mind you're always going to feed into a Dellorto float chamber from above no matter which spigot you choose to use!
The oil cooler analogy is not a good one. An oil cooler is fed from a sump. The oil pump feeds into the lowest point simply so that oil is allowed to drain back down through the lowest point to the sump when the engine is switched off . If it was fed from the top you'd be left with a cooler full of cold oil when you switched the engine on again.
Of course this will depend on where your oil cooler outlet feeds to. On the 500 it feeds to the cylinder head.
tom3c75
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- Location
- Cape Town South Africa
Lothar,
Interesting perspective.
I had a look at an old photo, taken soon after I took delivery of the bike when new, and the fuel pipe routing is exactly as shown in the pic above. So I expect that?s how the factory did it.
Interesting perspective.
I had a look at an old photo, taken soon after I took delivery of the bike when new, and the fuel pipe routing is exactly as shown in the pic above. So I expect that?s how the factory did it.
P
poffer
Guest
Well, since both inlet and outlet feed into the same fitting, both on the same side of the filter and with the holes less than 10mm apart, I can't see what difference it would make which way round you plumbed them......
Its a gravity system, so the petrol will percolate down through the pipes. The air won't, unless it has pressure behind it (and a few cm of height isn't nearly enough pressure :
)
Daft idea moving the pipes - been fine how they are for nearly 40 years 8)
Its a gravity system, so the petrol will percolate down through the pipes. The air won't, unless it has pressure behind it (and a few cm of height isn't nearly enough pressure :
)Daft idea moving the pipes - been fine how they are for nearly 40 years 8)
Dellortoman
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- Tasmania, Australia
It's an interesting point, and one I hadn't considered before.
Fluid dynamics is a very complicated area of study. You could probably do a PhD on the effect of encapsulated air on the flow of fluid in a pipe. In fact, I just did a quick google search and it seems people have done! "Fluid flow in partially filled conduits" is one thesis paper that popped up. I didn't bother reading it so I dunno how relevant it is to the situation we're talking about.
One thing I'm pretty sure about is that the static pressure created by the head of fuel in the tank above the carburettor is irrelevant. Static pressure won't purge air bubbles. Only a sufficient flow rate can do that. The flow rate in a fuel line to a carburettor is controlled by the float valve.
This is just wild speculation, but my educated guess is that an air bubble in a fuel line can under some circumstances have an effect on fuel flow. While a bubble is free to travel along a horizontal pipe with the flow of fluid, it will pop out the end without causing any problem. But if the flow is over a high point in a pipe where there is an encapsulated bubble, then the fuel will try to push the bubble down the descending side of the loop. At that point, the buoyancy of the bubble will exert an opposing force on the fluid. So it becomes a constriction of sorts - a bit like a moveable chicane in the pipe.
If the flow is only a dribble, then the bubble may remain at a high spot in the pipe while the fuel flows under it. But at dribbling flow rates (eg. engine at small throttle openings) any restriction due to the bubble is unlikely to have any detrimental effect.
If the fuel flow velocity in the pipe is sufficiently fast (I don't know whether wide-open throttle would induce a sufficiently fast flow, but lets assume it does) it will carry the bubble down along the pipe and through the float valve, where the air will escape via the float chamber vent. So the fuel line would be self-purging - no problem.
However, a problem may arise if at WOT (or more relevantly - wide open float valve) the fuel flow rate is insufficient to purge the bubble out of the line, but sufficient for flow to be affected by the restriction of the bubble. The fuel level in the float chamber may then decrease, causing the engine to run lean.
My Jota has the usual setup on the right side, where the fuel line does an upward loop from the petcock. But I've never been aware of any lean running problems on my bike that may have been related to air in the fuel line - possibly because I normally open both petcocks, so there's plenty of flow available via the balance pipe.
Anyway, if it bothers you to have a bubble in a loop of fuel line, just bleed it out: Disconnect the pipe from the carb, turn on the petcock and let the unrestricted flow flush the bubble out before you plug the line back onto the carby spigot (don't do it while smoking!). I'd be very surprised if air could re-enter the fuel line through the float valve against the fuel flow, so it should stay purged until you go on reserve and suck air in again.
Cheers,
Cam
Fluid dynamics is a very complicated area of study. You could probably do a PhD on the effect of encapsulated air on the flow of fluid in a pipe. In fact, I just did a quick google search and it seems people have done! "Fluid flow in partially filled conduits" is one thesis paper that popped up. I didn't bother reading it so I dunno how relevant it is to the situation we're talking about.
One thing I'm pretty sure about is that the static pressure created by the head of fuel in the tank above the carburettor is irrelevant. Static pressure won't purge air bubbles. Only a sufficient flow rate can do that. The flow rate in a fuel line to a carburettor is controlled by the float valve.
This is just wild speculation, but my educated guess is that an air bubble in a fuel line can under some circumstances have an effect on fuel flow. While a bubble is free to travel along a horizontal pipe with the flow of fluid, it will pop out the end without causing any problem. But if the flow is over a high point in a pipe where there is an encapsulated bubble, then the fuel will try to push the bubble down the descending side of the loop. At that point, the buoyancy of the bubble will exert an opposing force on the fluid. So it becomes a constriction of sorts - a bit like a moveable chicane in the pipe.
If the flow is only a dribble, then the bubble may remain at a high spot in the pipe while the fuel flows under it. But at dribbling flow rates (eg. engine at small throttle openings) any restriction due to the bubble is unlikely to have any detrimental effect.
If the fuel flow velocity in the pipe is sufficiently fast (I don't know whether wide-open throttle would induce a sufficiently fast flow, but lets assume it does) it will carry the bubble down along the pipe and through the float valve, where the air will escape via the float chamber vent. So the fuel line would be self-purging - no problem.
However, a problem may arise if at WOT (or more relevantly - wide open float valve) the fuel flow rate is insufficient to purge the bubble out of the line, but sufficient for flow to be affected by the restriction of the bubble. The fuel level in the float chamber may then decrease, causing the engine to run lean.
My Jota has the usual setup on the right side, where the fuel line does an upward loop from the petcock. But I've never been aware of any lean running problems on my bike that may have been related to air in the fuel line - possibly because I normally open both petcocks, so there's plenty of flow available via the balance pipe.
Anyway, if it bothers you to have a bubble in a loop of fuel line, just bleed it out: Disconnect the pipe from the carb, turn on the petcock and let the unrestricted flow flush the bubble out before you plug the line back onto the carby spigot (don't do it while smoking!). I'd be very surprised if air could re-enter the fuel line through the float valve against the fuel flow, so it should stay purged until you go on reserve and suck air in again.
Cheers,
Cam
If you have ever tried to remove the air bubbles in a water level,clear hose filled with water and it MUST be bubble free to work.As water finds it own level both ends of the hose show the same level point,very handy for cheap builders who don't own a Dumpy.The point of this is its not so easy to get a bubble free hose,try it with 30m of hose and you will go nuts.10m is achievable.The point it bubbles don't move easily on there own accord,takes some effort.
Laverdalothar
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- Germany
I wasn't maybe clear enough but Cam pointed in the right direction: the moment you change the direction of a tube, you produce a kind of siphon/p-trap and you will have massive issues getting these lines/tubes filled fully. Air-bubbles go to the highest point, in this case the upswing of the fuel-line. They will - as Cam rightly described - reduce fuel-flow by being a moving barrier. If you open the pet-cocks while not having this "air-trap", you will see that the bubble will not move down, but up to the pet-cock, which shows that the flow-rate of the pet-cocks are lower than the tendency of the bubble is to go upwards. If the bubble can't go upwards anymore as the next way either direction is downwards, it will probably stay there and just bounce backwards and forward, limiting the fuel-flow. This is a bigger of a problem as soon as the tank gets empty I would say...
Oh - and that the factory did it that way does not mean its right. It just assumes they never made any fault, which is proven to be wrong...
Why do you think they changed it to the 2-3 pipe on the later models? Right... better flow, equal feed to all carbs, no air-bubble-traps... They were not perfect, but they learned a lot... The earlier version was way cheaper than this specially welded, chromed tube. They should have taken plastic though, as the tubes tend to rust, but hey - I said they were not perfect, right?
To mount the tube to the lower part has 2 advantages for me: 1.) it builds a kind of "rust-trap" if you let the fuel-line go below the carb-feed first and 2.) it avoids air-bubbles in the system.
Oh - and it looks way better, too, but that is personal taste, right?
Oh - and that the factory did it that way does not mean its right. It just assumes they never made any fault, which is proven to be wrong...
Why do you think they changed it to the 2-3 pipe on the later models? Right... better flow, equal feed to all carbs, no air-bubble-traps... They were not perfect, but they learned a lot... The earlier version was way cheaper than this specially welded, chromed tube. They should have taken plastic though, as the tubes tend to rust, but hey - I said they were not perfect, right? To mount the tube to the lower part has 2 advantages for me: 1.) it builds a kind of "rust-trap" if you let the fuel-line go below the carb-feed first and 2.) it avoids air-bubbles in the system.
Oh - and it looks way better, too, but that is personal taste, right?
D
Davo
Guest
Easier just to turn on the fuel tap and push on the fuel line, lowering the line so that the bubble moves up into the tank, eh Cam. That is of course if you are worried about it.
Laverdalothar
Hero member
- Location
- Germany
Not so easy if your fuel line is older than a year and has ever been emptied completely for longer than some days. It tends to get a hard-plastic consistency with a tendency to brake just by the vibrations of the engine. Pushing it down every time you open the pet-cocks will brake it over time for sure. Also: when ever the tank gets empty and you corner with the bike, the gas in the tank will not reach to both pet-cocks anymore and the system automatically sucks air. You would need potentially to push down the tubes after every corner then... Not sure that makes sense?!? 
Cosi
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- Location
- Kingscliff
fill up every 200ks Lothar, my ass is ready for a walk about then
D
Davo
Guest
Hell Lothar, if my fuel hoses got that brittle...
Nah, not going to happen, I would have changed them well before they got that brittle.
And as for leaning the bike so far over in a corner that you completely empty the high side of the tank - well - speechless
Nah, not going to happen, I would have changed them well before they got that brittle.
And as for leaning the bike so far over in a corner that you completely empty the high side of the tank - well - speechless
VanguardontheLav
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- Cambridge, UK
Laverdalothar said:
No, the gas stays central to the bike, just like you do... Bad science there!
--
Dick
P
poffer
Guest
Again, it's a gravity fed system. The air bubbles present only a minute (or no) resistance on a gravity system. For the bubbles to present any resistance, the fluid would need to be fed under pressure.
If you want to test the theory: Empty the float bowls and (once you have put them back on :-* ), open the fuel taps. The fuel flows fine and fills the bowls faster than WOT will consume it. There isn't a problem and the best suggestion comes from Paul Marx "For anybody worried, I recommend using non transparent petrol pipe." Wise words 8)
Also - consider the relative sizes of the tap outlet and the pipe. Tap outlet is no more than 4mm (probably nearer 3mm), pipe ID is 6mm. This means the area of the tap outlet is max. 12 mm2 and the area of the pipe is approx. 28mm2. I can assure you that the tap is far more restrictive than any air bubble :
And don't anyone dare mention cavitation on a gravity fed system, or I will come round their house and beat them with a petrol pipe (Cavis Benz, of course )
Pete
If you want to test the theory: Empty the float bowls and (once you have put them back on :-* ), open the fuel taps. The fuel flows fine and fills the bowls faster than WOT will consume it. There isn't a problem and the best suggestion comes from Paul Marx "For anybody worried, I recommend using non transparent petrol pipe." Wise words 8)
Also - consider the relative sizes of the tap outlet and the pipe. Tap outlet is no more than 4mm (probably nearer 3mm), pipe ID is 6mm. This means the area of the tap outlet is max. 12 mm2 and the area of the pipe is approx. 28mm2. I can assure you that the tap is far more restrictive than any air bubble :
And don't anyone dare mention cavitation on a gravity fed system, or I will come round their house and beat them with a petrol pipe (Cavis Benz, of course
)Pete
poffer said:And don't anyone dare mention cavitation on a gravity fed system, or I will come round their house and beat them with a petrol pipe (Cavis Benz, of course
But use a nicely seasoned bit, Pete!
In over 30 years of Laverda triple ownership, never have I experienced problems with fuel feed. Taps, hose and carb unions are all up to the job. Never even considered swapping them for something else! Hose routing only has an influence if it is draped OVER the tank...
The Breganze boys got it right from the start.
piet
sfcpiet said:poffer said:And don't anyone dare mention cavitation on a gravity fed system, or I will come round their house and beat them with a petrol pipe (Cavis Benz, of course
But use a nicely seasoned bit, Pete!
In over 30 years of Laverda triple ownership, never have I experienced problems with fuel feed. Taps, hose and carb unions are all up to the job. Never even considered swapping them for something else! Hose routing only has an influence if it is draped OVER the tank...
The Breganze boys got it right from the start.
piet
No wonder the bikes aren't ridden much!
Ciao
Paul
markQLD
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- QLD Australia
reckon if a bloke is concerned, than leave all the bowls off, and they will soon see just how much fuel pours out over the motor?poffer said:
and,, i strongly suggest ya don't hit the starter with fuel pouring over it!!
cheers, Mark
chrisk
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- Brisbane, Australia
Mark, is it best not to be smoking at the time? (bang)