11 replies to this topic

[Frischkäse]

Hey Folks,

I just installed a pair of fresh rebuilt HS4s. They are synchronised and should have the right needle and spring.
If the fuel pump is turned on, the left carb leaks a bit of fuel out of the overflow. Also there is always a bit of fuel in the carb, even when the engine was running. The left carb is always dry, the right carb is always wet. Both carbs and all 4 cylinders are running.
What is the problem here? May be the float level to high? Or is the synchronisation messed up?

An answer would be nice!

[panky]

More than likely the float valve is passing slightly, maybe a little bit of debris under the seat.

[Frischkäse]

May be, but it would not cause an always wet carb, would it?

[carbon]

Do you have a filter fitted in the petrol line?

[panky]

If the valve is passing and the float chamber is over full then that carb could be over-fuelling. What type of fuel pump is fitted, it could be it's running at too high a pressure.

[Frischkäse]

Sorry for the late answer, the garage is far away.
The fuel pump is a Hüco 13 3010. It has 2,2 PSI and 130 l/h. With the earlier fitted HIF44 the pump stopped at a certain pressure.

I have no filter in the line, but will fit a new one.

The float needle valve is clean, but hangs sometimes a litte on the upper position. If I blow through the inlet line, the valve opens immediately. Also the valve closes complete, if I push the float bowl upwards. Its a full plastic type bowl, so there is nothing to adjust.

So, are there any other ideas? I have another float needle valve, that I will fit tomorrow, to check the possibilities.

[Spider]

It sounds to me like the fuel level is too high in that fuel bowl. Adjustment of these later types is done by fitting different thickness washers under the seat of the needle and seat. A very small change makes a huge difference, so be prepared for it to take a while to sort. I managed to get a hold of some soft aluminium washers a while back, so the fine tuning can be done by how tight they are done up. Tighter increases fuel level.

[carbon]

When I had problems with dirt in fuel line it was always the same one of the carbs which overflowed. Can't recall which one, but the fuel filter sorted this and never had a problem since.

 

But when fitting a fuel filter:

- cheap plastic ones have been known to fail when running fuel containing ethanol. If you're putting a filter close to the carb make sure it's a decent quality housing, not a brittle plastic as you are close to a very hot exhaust manifold...

- also worth checking the fuel flow is not affected if you're running higher output motor. With electric pump connect a length of hose to outlet from filter and run into jerrycan, to check how much weight of fuel you get in about 10 minutes

[Frischkäse]

Thanks for the replies. A too high fuel level explains the overflow quite well. I will fit the filter and check the fuel flow. I also will search for those shims as well.
But the other problem, with the fuel inside the carb wont be explained, will it?

[Spider]

Thanks for the replies. A too high fuel level explains the overflow quite well. I will fit the filter and check the fuel flow. I also will search for those shims as well.
But the other problem, with the fuel inside the carb wont be explained, will it?

 

That in particular is what tweaked me to it being too high a fuel level.

[Frischkäse]

Just for understanding: Does the higher fuel level cause higher pressure in the float chamber and so more fuel flow to the needle? Or what is the matter?

[Spider]

Just for understanding: Does the higher fuel level cause higher pressure in the float chamber and so more fuel flow to the needle? Or what is the matter?

 

The higher fuel level brings the level up in the jet to the point where it can free flow out the top.