SOHC.co.uk Forums > CB750
Head Bolts
Oddjob:
Exactly what I was trying to say Ted, we blame the height of the remote fuel container instead of looking for the reason it’s leaking, reasons like debris under the seat or poor manufacture of the float seat etc, the higher position of the remote container just makes the existing problem worse. A good seal isn’t bothered by the raised height.
K2-K6:
--- Quote from: Moorey on January 20, 2024, 10:04:31 AM ---
Typically mc fuel pumps delivers 3psi. Float valves are generally overcome at approx 4.5 / 5psi. 1ft head of water gives 0.433psi do the maths.
One thing many don't think of is that in use float valves open very tiny amounts so the smallest of debris is likely to stay in the valve and never
be flushed through unless the carb is drained or stripped and cleaned properly.
Anyone wanting to check simply put a airline with a pressure reg on a upside down carb on the carb inlet and see at what point the valve leaks
air when using leak detector spray.
--- End quote ---
Isn't that accumulated figure 0.433 psi going downward under sea level ? Usually at one atmosphere for each 10.06 mtrs (33ft) effectively the accumulation of the ocean above you.
In air, and by lifting 1 ltr, then its nothing like that surely.
I'd doubt much difference between a tank say at 20 ltr sitting just above the carbs, in comparison to 1 ltr at 6 ft higher.
taysidedragon:
I hang my temporary tank on the bars because otherwise you have to extend the fuel line to reach the rafters.
Why use 6ft when you can just use 2ft? 🙂
McCabe-Thiele (Ted):
--- Quote from: K2-K6 on January 20, 2024, 02:55:49 PM ---
--- Quote from: Moorey on January 20, 2024, 10:04:31 AM ---
Typically mc fuel pumps delivers 3psi. Float valves are generally overcome at approx 4.5 / 5psi. 1ft head of water gives 0.433psi do the maths.
One thing many don't think of is that in use float valves open very tiny amounts so the smallest of debris is likely to stay in the valve and never
be flushed through unless the carb is drained or stripped and cleaned properly.
Anyone wanting to check simply put a airline with a pressure reg on a upside down carb on the carb inlet and see at what point the valve leaks
air when using leak detector spray.
--- End quote ---
Isn't that accumulated figure 0.433 psi going downward under sea level ? Usually at one atmosphere for each 10.06 mtrs (33ft) effectively the accumulation of the ocean above you.
In air, and by lifting 1 ltr, then its nothing like that surely.
I'd doubt much difference between a tank say at 20 ltr sitting just above the carbs, in comparison to 1 ltr at 6 ft higher.
--- End quote ---
The volume of petrol in either tank is not the issue here that would only alter the flow level if both tanks were of the same depth.
My previous sums were out by a factor of two as a 66 ft water tower would represent 2 Atmosphers about 60 psi not 30 psi - so a foot of water is around 0.9 psi the total volume of fuel in either the bike tank or the temporary one is irrelevant. So at 6 ft above the existing petrol tank of say 1-ft the pressure would rise from 0.9 psi with an increase of 6 x 0.9 = 5.4 making the total pressure at effectively 0.9 + 5.4 = 6.3 psi. This does not take into account the difference in density between water & petrol , all pressures are based on sea level.
K2-K6:
It's making me intrigued as to what is correct, not because it's in any way practical.....for reference, I use a plastic syringe about 100ml stuck into the fuel feed pipe and secured to frame by elastic band when carb balancing. Same one has been in my tools since the seventies :)
Can we apply the "atmosphere" calculation to a static head of fluid though ? The example of going down intomthe sea doesn't seem to apply to me as you are effectively within the fluid that is supported on the seabed. Each movement downward gives you a layer now above you that's compressive. The total gain taking into account that increases in mass to give the typical calculation figure.
In water tower or the high level fuel feed, the mass is supported through a route down to the ground and so doesn't enact a force on the outlet.
The column weight is what we could measure at base level, this then depending on bore size (capacity in vertical now unsupported by the structure) with a column of 60 ltrs that would be 60 kilos in water into whatever sized outlet we have.
Oil derived fuels are ordinarily less dense than water, but not by much to affect our consideration here.
It looks more like volume of pipe above float valve (possibly 100 ml ) when on ceiling, approx 100 grams resisted by the float force through leverage on the entry valve.
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version