Float Vent Connection
Turbo Mini Forums

I have converted an Nat Asp carb to use on the turbo.

Is the float vent the same as the part throttle lean off pipe?

Currently I have it connected back to tank via its own low pressure feed. Will this cause issues when I come onto boost?

Am driving at the mo under the boost threshold. And so far seems fine. (It needs setting up on the rollers because the needle profile is all wrong and far too lean when coming on boost.)

1275 N/A Sprite, 998 T2 Turbo Mayfair
1275 EFi Turbo

No, the float vent is not the same as the part throttle lean off. It is just that a float vent.

If it's not blocked up when you come on boost it'll just squirt fuel out. I think the way you have it connected will stop the float bowl pressurising.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

ok thanks wil.

I initially blocked it off but i had air in the float chamber that mean the float didn't ..... float.

I will block it off again now the air is purged. Presumably no more air should get it.

1275 N/A Sprite, 998 T2 Turbo Mayfair
1275 EFi Turbo

Seems a bit odd. The float bowl isn't exactly sealed, i.e. if you pump fuel in at a pressure above the needle valve release pressure it fills the bowl up then squirts fuel out of the jet.

So not much chance of an air lock.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

I know. Confused me too. But fuel was pouring out the jet and i'd tried everything else. SO I unblocked the float pipe, air fizzed out and problem solved.

1275 N/A Sprite, 998 T2 Turbo Mayfair
1275 EFi Turbo

If I now try to block the pipe back up it causes fuel to dribble out of the jet (when needle removed)
Also, when the engine is running the car tries to die when the pipe is blocked off

1275 N/A Sprite, 998 T2 Turbo Mayfair
1275 EFi Turbo

Right, your problem is that your fuel pressure is set too high.

I presume that you have the Metro fuel pressure regulator and pump, and that there is a good return pipe to the fuel tank.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

Ive had a faulty needle valve before that caused the same problem.
That was a new one that caused the problem so dont presume it is ok

Good point Nic. Checking the fuel pressure will answer which one it is.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

Right, Actually sorted now.

Turns out that on my carb (I think it's a maestro or metego one, it has the casting in place for auto choke system) the drilling between plenum and carb to pressurise the float chamber was plugged.

So when I blocked off the vent connection there was no vent at all in the chamber and so fuel dribbled up the jet.

It also meant that trying to come on boost was like hitting a brick wall. There was no fuel at all at anything near or past atmospheric.

Drilled out the blank and problem all fixed. No dribbling fuel, able to boost. Fantastic!


Note also my woes here (presumably caused by that same drilling).

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=383809

1275 N/A Sprite, 998 T2 Turbo Mayfair
1275 EFi Turbo

Even with the drilling blocked up no fuel should come out of the jet (with the engine off and pump on).

You still need to check the needle valve and fuel pressure IMO.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph