Huco pump not shutting off

[JohnFol]

Finally fitted a Huco 13310 to a carb engine (vertically) Spins up fine suggesting inertia switch, relay and pump wiring all good and engine gets good supply of fuel(as seen in fuel filter before pump)
I've done the crude "blow down return pipe"so I know it's clear.
Pump described as not needing regulator so I'm expecting the pump to automatically stop when not required.

Quick test shows with engine off the pump continues to pump. I can hear it "pulsing" under strain and it's clear it's trying to pull more fuel.

Any suggestions?

[peteracs]

Hi John

A couple of questions....

You say engine off and still running, do you mean engine off and ignition off, or engine not started but ignition on?

If you have the return pipe still active, there will be no back pressure on the pump, hence the pump will keep pumping I would have thought?

Peter

[JohnFol]

Just clamped the return pipe from carb and it shuts down.

I had assumed the carb float acts a bit like a ball valve giving back pressure.


Many thanks

[WestonE]

Hi John

normally with interrupter pumps the return is deleted. I strongly recommend a filter king regulator set to 3PSI. You will consistently have the right pressure avoiding rich running from the float needle being pushed open and all you need for full bore fun.

Eric   

[peteracs]

Just clamped the return pipe from carb and it shuts down.

I had assumed the carb float acts a bit like a ball valve giving back pressure.


Many thanks

That poses a good question. I understand why with a mechanical pump there is a return, but without going back to my carb, does the return come off the float chamber or is it before that, which means the float does its job and you still get a flow of fuel?

Peter

[JohnFol]

I'm expecting the Huco to run at 2.2 psi so not sure capping it with a regulator will take pressure off the float.  Need to read up more to see if I can understand Peter's question more.

[mangocrazy]

Mechanical fuel pumps need a return path as they have no means of not pumping once the float bowl is full. Electric pumps sense resistance when the float bowl is full and (when working correctly) stop pumping. As you surmised, with a return path available using an electric fuel pump, the pump will continue pumping as it never sees resistance. Agree about not needing a fuel regulator, as the Huco fuel pump is self regulating and is set at a lower pressure than 3 psi.

[JohnFol]

I had a fuel non return valve in the garage so just added it in reverse (after carb) and all ok. First few drives were anxious but good.

[JohnFol]

Just noticed the pump shuts off once it reaches a certain point, but it then has small pulses roughly every 10-15 seconds. I then clamped the return pipe to rule out a dodge non-return value and same thing.

Decided to take plunge and get carb refurnished, but interested to hear if this is a candidate for pressure regulator, as I can be looking at that whilst carb is away

[Nigel]

Hi Jon,
Mine does the same, short pulse after 15 secs or so.
My return line is inactive,ever since I fitted the Huco.

It seems to deliver adequate fuel as i've no hesitation even up at 80mph.
My CO2 reading is 3.1 ,which is close to MOT max.

Rgds
Nigel

[JohnFol]

Thanks Nigel, ways good to get a 2nd opinion

[JohnFol]

If the float chamber has a needle valve to stop fuel entering carb when float is up, why doesn't that cause enough back pressure to shut huco off?
Adding a non return on the "overflow" side of the carb just means any surplus can only go into the engine.

[Nigel]

If the float chamber has a needle valve to stop fuel entering carb when float is up, why doesn't that cause enough back pressure to shut huco off?
Adding a non return on the "overflow" side of the carb just means any surplus can only go into the engine.

Hi John,
The float needle valve on mine stops the Huco pump running when the chamber is full.
But, I also have an inline device just before the inlet to the carb. I have always assumed it's
a pressure regulator unless I get corrected! It appears to have been a factory fitting.
Edit to add: the pump does still give a burp every 5/7 secs though, as if it's 'testing'
for requirements.

[JohnFol]

I'd say the 1st picture shows a non-return valve, but I could be wrong.

...and yes, I get the burping as well