Okay , so the little lady was angry after a few months of neglect. Had to have the gas tank welded and POR-10 'd. So in my rush to make her happy again I failed to take note of the fuel line placement.

I had pulled all the fuel lines(from the tank as well as the dual DCNF's) to get the tank out (figured I would replace all the fuel lines and filter again).

However , I have forgotten where the two vent tube lines in the tank go.......

Attached is a rough (very rough) image of what i think it should be.

However , when all is piped up as it shpould be(i think) , that leaves me the two vent tubes on the tank.

Where do they go??

Feel like such a git but can't recall for the life of me.....

Please help!

I'm a little confused as to the setup you have running.

First of all where is your fuel pressure regulator? Or are you running a low pressure pump?

The tank does not normally run a vent, instead you have a return pipe from the carburettor. Obviously you don't have a return pipe so the return apperture should be blanked off or at the very least have a few coils of open pipe to prevent spillage in the event of the car rolling over.

As to which pipe is which on the tank, I just can't remember which is which any more.

The outlet is the top one, the bottom is the return.

I will snap some photo's when i get home and see if that helps. Of note though , there is no regulator. Just the mechanical fuel pump, the two DCNF's, an inline fuel filter, and the two plastic tube things (not sure what the tech term is) that mount to the firewall on either side of the fuel pick up in the tank.

You're still running the mechanical pump? Blimey, now I am impressed - impressed that it all works that is.

I wouldn't expect any problems except at top end but even still it is pretty much a defacto upgrade to switch to an electric fuel pump, even a low pressure one (it isn't uncommon to see these on cars with standard carburettors) just because they are so much more reliable at maintaining the necessary flow and pressure and you don't need the engine turning to prime the system.

The downside is that you don't have a safety cutout in the event of an accident.

The pressure regulator is another safety feature. Even a mild fast road pump can provide too much pressure for the delicate float chamber valves so a regulator is fitted to compensate. These tend to be quite simple devices - just two flaps of rubber pushed together by a spring with adjustment on the spring tension. More expensive versions incorporate the fuel filter in a single unit.

I am running a low pressure pump on my standard carb...

What sort of fuel pressure should be used on DCNF's Jimbro?

Okay , so I think I have figured it out! In the attached picture you can see the plastic tube mounted to the firewall which is connected to the tank. I think that is, as mentioned above, just a loop that connects to the top two vent tubes (circled in yellow). Which would mean that the fuel supply line is connected to the wrong thing!

As for the comment about losing power from the mechanical pump , well, the only issues I have had are low rpm (750-1300rpm) driving. There don't seem to be any top end issues. I have had this car up to the 150km/h range with no issues or lack of power, either getting it to that speed or maintaining it.

As for the vent, the tube has a one way valve so fluid can come out but not go in as opposed to just being blanked.

It would seem i need to take a little more care in noting where things go when i take them off!

Weber DCNFs normally run between 3 and 3.5psi. They can run on less than that but 3.5psi is about where the needle valves on the float chambers tend to give up and just let fluid through anyway.

The important thing isn't so much the pressure (this is just a yardstick) it is the flow rate. The flow rate is going to depend on how much fuel you use at peak load.

If the engine is still producing near stock power figures then the mechanical pump is still acceptable (but prone to vapour lock and startup problems). Anything over 100bhp (this is a ball park figure - it really depends on the engine and fuel pump) and the pump will start to let the carbs run dry, this in turn results in loss of power and over heating. You tend to find that the engine feels like it has run out of go. You might not notice it in lower gears but in 4th or 5th it feels like the engine is very flat in the upper half of the rev range. The more power the engine produces the worse it gets.

A 130bhp engine would need a fairly hefty pump, you could get away with an electric fast road pump but you are nearing the limits of what it can do. Past 150bhp and you really need a competition grade pump. These bigger pumps run higher pressure and really need a regulator.

:yeahthat: I am surprised to see that the standard pump is still in use, every twin carb after-market set up I've made or worked on needed the electric pump and a fuel regulator, a must IMHO.
I'm reasonably confident that better running would be had with the full set up applied.

So a few days have passed and I finally had time to get everything back together. However a question or two has come up now.

1. should the stock mechanical fuel pump have a part number on it?

2. If so where is it located?

It would seem that the pump I have on the car has no identifying marks on it anywhere. Begs the question of "is this the original pump?"

From what I gather the p/o was in the process of building the car up to do short track autocross. He had mentioned that he had done the cam, pistons, valves, etc etc but couldn't remember what else exactly was in it seeing as it sat for 5 years and he had moved onto other things.

Anyhow , as luck would have it, when I went to fire it up after everything was back in it would appear that the starter has frozen. It will be back from the rebuilder tommorow.

The saga continues!

The part number for the pump is 4316006. Same as Beta according to my reference.

Well , tonight went well. Starter in , fuel lines checked again , carbs back on. 15l of hightest in................

end result in the following link (3mb video file)

http://l8agn2.tripod.com/http://l8agn2.tripod.com/sitebuildercontent/sitebuilderfiles/itlives2.mpg (click on "results afetr fuel system fix")

As for the fuel pump , still odd that there are no markings on it. Does anyone know if the Sprint filter/manifold setup came with an uprated mechanical fuel pump? Or was it just the manifold and carb cover?

Can't get that link to work properly, no video file

Works for me - I listened to it this morning but there is a rattle in the audio stream that I can't tell if it is the video compression or the engine...

The rattle would be the compression codec I had to use to get it to comply with size and type on Tripod. Still not bad for a cell phone video though!

Just happy that it seems to run as it should for the most part. Now I can take it in and get the carbs jetted and synced again!