SU carb float chamber not filling

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splitscreen
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SU carb float chamber not filling

Postby splitscreen » Wed Dec 04, 2019 9:53 pm

The carb float chamber won’t fill with fuel despite the pump working and send fuel through the pipe. When the pipe is attached to the float lid it stops. I’ve cleaned out the float but this has made no difference.
Any ideas as to what’s wrong?

pgp001
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Re: SU carb float chamber not filling

Postby pgp001 » Wed Dec 04, 2019 10:21 pm

Is the float needle stuck onto the seat ?
Have you tried blowing into the fuel inlet pipe on the carb to see if it is clear ?

Phil

oliver90owner
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Re: SU carb float chamber not filling

Postby oliver90owner » Wed Dec 04, 2019 10:23 pm

You have a blockage between feed pipe and float chamber - either crud or a stuck float valve (or possibly wrongly fitted, if it has been tampered with.

kennatt
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Re: SU carb float chamber not filling

Postby kennatt » Thu Dec 05, 2019 8:46 am

easy to check take top off and when float drops the little needle valve in the top should be loose and hanging down give it a bit of a twist or poke up and down. If its stuck once it will likely need a new valve assembly because its liable to do it again or stick open causing flooding. No doubt that's the problem.

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philthehill
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Re: SU carb float chamber not filling

Postby philthehill » Thu Dec 05, 2019 10:29 am

Check the inside of the flexible rubber pipe from fuel pump to carb.
The pipe has a tendency to delaminate and when the pipe is fitted the centre of the centre of the pipe curls up and blocks the fuel from going through.
I would replace the pipe as a matter of course. Make sure that the pipe is suitable for unleaded/ethel fuel.
It is quite rare for the float chamber needle to stick in the closed position.

What SU have you got fitted? A picture of the carb would be appreciated.


splitscreen
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Re: SU carb float chamber not filling

Postby splitscreen » Thu Dec 05, 2019 11:03 am

Thanks for the responses.

The pump sends fuel through the rubber pipe but this stops when the pipe is connected to the float chamber. There doesn't appear to be a blockage in the brass inlet pipe on the chamber lid. The valve moves up and down when pushed with a screw driver.

It's the standard HS2 11/4" carb.

mogbob
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Re: SU carb float chamber not filling

Postby mogbob » Thu Dec 05, 2019 11:40 am

The needle in the inlet valve should "move freely " with just the merest gentle touch of a finger. A slow motion
upward flick of the finger should see it rise and fall immediately. If you're having to use a screwdriver to force it to move then it does need replacing. Take Phil's advice onboard of checking out the possibility of a disintegrating rubber delivery hose.
Bob

splitscreen
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Re: SU carb float chamber not filling

Postby splitscreen » Thu Dec 05, 2019 2:15 pm

I don't have to force the needle with the screw driver tip - I'm only using this as I can't get my finger in the gap with the float still attached to the lid. It moves easily.
With regard to the rubber pipe if fuel can be pumped through it when it's not connected to the chamber lid surely it can't be blocked?

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philthehill
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Re: SU carb float chamber not filling

Postby philthehill » Thu Dec 05, 2019 5:01 pm

The standard HS2 SU carb float chamber float chamber valve is not prone to sticking and you have indicated that the needle moves freely.

Again I would say replace the hose from pump to carb. The inside can easily delaminate/break up and appear to be serviceable when not connected to the float chamber. If the hose is original it is not suitable for use with unleaded/ethel fuels anyway. Any fuel hose purchased should be marked as suitable for unleaded/ethel fuels.

Take the float chamber lid off and blow through the brass inlet pipe - it may be that some of the rubber pipe segments are blocking the passage through the float chamber lid. If you can blow through it must be the hose.


splitscreen
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Re: SU carb float chamber not filling

Postby splitscreen » Thu Dec 05, 2019 5:13 pm

philthehill wrote:
Thu Dec 05, 2019 5:01 pm


Take the float chamber lid off and blow through the brass inlet pipe - it may be that some of the rubber pipe segments are blocking the passage through the float chamber lid. If you can blow through it must be the hose.
I'll give it another go and as I have a new rubber hose will fit that to see if that makes a difference.

Again, thanks for the advice.


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