Engine full of fuel.

[Pegleg]

Anyone know if the electric inline pump will let fuel through when its not running? Carbs have held up for weeks til I fitted a 10mm outlet to the tank without a tap yesterday. Engine full of fuel this morning. Original tap was used in the prime position previously. 

[DAZ]

I would image it could allow some seepage it's not an interference fit after all ,but out of interest how much fuel was in the tank as I'm thinking maybe a full tank would create more "pressure" , I think it's called head weight ,think of a water tank in the loft it give more pressure to the taps downstairs Etc , and maybe the old tap caused enough restriction even on prime to lessen the pressure so that it wasn't an issue 

Edit2 : I think the bore of a fuel tap is 6-8 mm so area wise you've increased it a lot more than just say 2mm the cross sectional area will have increased by 50% at a guess

Edited October 13, 2023 by DAZ
Bleeding predictive text and addition

[Pegleg]

Was about third of a tank. Seems like a coincidence it was ok before. I'll get an inline tap. Trying not to restrict the flow to sort fuel starvation issue. Thanks @DAZ

[imago]

22 minutes ago, Pegleg said:

Was about third of a tank. Seems like a coincidence it was ok before. I'll get an inline tap. Trying not to restrict the flow to sort fuel starvation issue. Thanks @DAZ

It's possible that you've found the issue. If the in line pump is letting fuel through when it's off then it's unlikely to be able to shift sufficient volume when it's running. 

[Pegleg]

21 minutes ago, imago said:

It's possible that you've found the issue. If the in line pump is letting fuel through when it's off then it's unlikely to be able to shift sufficient volume when it's running. 

Ah. I'll test it with a full tank when I've fitted a tap. 

[wombat258]

Check carb float needles and the seat o-rings for leakage. With pump off they should not leak with normal head of fuel.

[Pegleg]

14 hours ago, wombat258 said:

Check carb float needles and the seat o-rings for leakage. With pump off they should not leak with normal head of fuel.

They havn't leaked once since I started putting the bike together Months ago. I've done several carb rebuilds now. Seems strange they suddenly leak after getting stronger fuel supply. I will strip them again. Might have got a bit of swarf through when I fitted the bigger outlet.  

[Gixer1460]

Really, the 'prime' position isn't meant for running the engine although people do - its purpose / action is, to lift the diaphragm marginally to fill the float bowls on empty carbs - after a rebuild or after running out of fuel. The gap isn't designed for long term, full power fuel flow! Adding a fuel pump would mask a problem, not improve it as the pump will try to draw more fuel than the tap can deliver in 'prime' position.

A Pingle tap (for instance) has a single in-tank delivery pipe with a 6mm bore - doesn't make any difference if tap has 1, 2 or 3 outlets - it has one 6mm bore pipe from tank . . . . and that is enough for over 350+ turbo EFI hp ! The float valves in the carbs, at the needle valve, have a 1.5mm ? opening which across 4 carbs = 28.26 sq mm (approx) and a Pingle has a pipe bore area of 113.04 sq mm. Your 10mm tank outlet has an area of 314 sq mm.

So, the tank outlet is 11 times larger than the carbs can utilise, but its size reduces the potential flow restriction and increasing the pressure seen at the float jets - its a miniscule increase but maybe enough to tip over the edge?

[wombat258]

9 hours ago, Pegleg said:

They havn't leaked once since I started putting the bike together Months ago. I've done several carb rebuilds now. Seems strange they suddenly leak after getting stronger fuel supply. I will strip them again. Might have got a bit of swarf through when I fitted the bigger outlet.  

Or, a float could have collapsed/cracked and contains fuel.

[Pegleg]

On 10/14/2023 at 1:26 PM, Gixer1460 said:

Really, the 'prime' position isn't meant for running the engine although people do - its purpose / action is, to lift the diaphragm marginally to fill the float bowls on empty carbs - after a rebuild or after running out of fuel. The gap isn't designed for long term, full power fuel flow! Adding a fuel pump would mask a problem, not improve it as the pump will try to draw more fuel than the tap can deliver in 'prime' position.

A Pingle tap (for instance) has a single in-tank delivery pipe with a 6mm bore - doesn't make any difference if tap has 1, 2 or 3 outlets - it has one 6mm bore pipe from tank . . . . and that is enough for over 350+ turbo EFI hp ! The float valves in the carbs, at the needle valve, have a 1.5mm ? opening which across 4 carbs = 28.26 sq mm (approx) and a Pingle has a pipe bore area of 113.04 sq mm. Your 10mm tank outlet has an area of 314 sq mm.

So, the tank outlet is 11 times larger than the carbs can utilise, but its size reduces the potential flow restriction and increasing the pressure seen at the float jets - its a miniscule increase but maybe enough to tip over the edge?

That all makes perfect sense @Gixer1460 I'm gonna try the 8mm fitting I had fitted before. Might even experiment with flow rates. See what difference is. 

[Reinhoud]

Your carburetors are faulty, the float needles should seal off the fuel supply.

[Pegleg]

3 hours ago, Reinhoud said:

Your carburetors are faulty, the float needles should seal off the fuel supply.

As @Gixer1460said above. I have dramatically increased the flow which might be overwhelming the needles. They didn't flood with an 8mm fitting. 

[wombat258]

20 hours ago, Pegleg said:

As @Gixer1460said above. I have dramatically increased the flow which might be overwhelming the needles. They didn't flood with an 8mm fitting. 

No. If the floats were doing their job you could have a 3" diameter pipe feeding it without it flooding, with the fuel pump turned off. One advantage of the vacuum operated tap is that it shuts off fuel flow to the floats while the engine is not running.

[Pegleg]

2 hours ago, wombat258 said:

No. If the floats were doing their job you could have a 3" diameter pipe feeding it without it flooding, with the fuel pump turned off. One advantage of the vacuum operated tap is that it shuts off fuel flow to the floats while the engine is not running.

Surely the weight of fuel would over come the floats? Trying to eliminate a fuel starvation issue. Vacuum tap would be great if it flowed enough. 

[TonyGee]

20 minutes ago, Pegleg said:

Surely the weight of fuel would over come the floats? Trying to eliminate a fuel starvation issue. Vacuum tap would be great if it flowed enough. 

if you are talking about a "standard" set up then a full tank of fuel shouldn't overcome the floats, but it is possible especially if the tank builds up with pressure if the breather is not doing its job or on a hot day.   this is why they fit a tap between the tank and the carbs.  

[peter1127]

vacuumtap wouldnt work: it closes under boost 

Diameter of fuel tap doesnt matter in static situation. Only the height difference between top of fuel  and bowls result in pressure.  Needles & seats need to be in perfect condition on a turbo bike to deal with the fuel pump pressure anyway.  Best open it up and check, and replace when in doubt. Could also be debris which entered the system when working on the fuel system, or a ruptured filter.

[Reinhoud]

Fuel is leaking when fuel pump is running? Lower the pressure to about 1.5psi

[wombat258]

On 10/18/2023 at 2:03 AM, peter1127 said:

vacuumtap wouldnt work: it closes under boost 

 

Actually it can with a small bit of engineering. I managed to get a constant vacuum source to a Scottoiler on my turbo engine with a small check valve and a small electric solenoid

[peter1127]

10 hours ago, wombat258 said:

Actually it can with a small bit of engineering. I managed to get a constant vacuum source to a Scottoiler on my turbo engine with a small check valve and a small electric solenoid

creative!

[Pegleg]

On 10/14/2023 at 1:26 PM, Gixer1460 said:

Really, the 'prime' position isn't meant for running the engine although people do - its purpose / action is, to lift the diaphragm marginally to fill the float bowls on empty carbs - after a rebuild or after running out of fuel. The gap isn't designed for long term, full power fuel flow! Adding a fuel pump would mask a problem, not improve it as the pump will try to draw more fuel than the tap can deliver in 'prime' position.

A Pingle tap (for instance) has a single in-tank delivery pipe with a 6mm bore - doesn't make any difference if tap has 1, 2 or 3 outlets - it has one 6mm bore pipe from tank . . . . and that is enough for over 350+ turbo EFI hp ! The float valves in the carbs, at the needle valve, have a 1.5mm ? opening which across 4 carbs = 28.26 sq mm (approx) and a Pingle has a pipe bore area of 113.04 sq mm. Your 10mm tank outlet has an area of 314 sq mm.

So, the tank outlet is 11 times larger than the carbs can utilise, but its size reduces the potential flow restriction and increasing the pressure seen at the float jets - its a miniscule increase but maybe enough to tip over the edge?

@Gixer1460Any particular Pingel you recommend? Decided to bite the bullet and spend the money. 

[Gixer1460]

I have no particular preference as if I have a two outlet tap and only one line to carbs, I just block the spare or convert carbs to have two separate feeds.

If you are handy with tools, a tank adapter block and an in-line, ball valve tap could save a chunk of money?

[Pegleg]

58 minutes ago, Gixer1460 said:

I have no particular preference as if I have a two outlet tap and only one line to carbs, I just block the spare or convert carbs to have two separate feeds.

If you are handy with tools, a tank adapter block and an in-line, ball valve tap could save a chunk of money?

I've made an adapter with a 10mm push on fitting. The only inline ball valve taps I can find only have a 6mm bore. They're also quite a big lump to find space for.

[Pegleg]

Also finding room for an unrestrictive fuel filter is a challenge.