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Mark Taxis
Prolific User
Username: mark_taxis

Post Number: 145
Registered: 4-2007
Posted on Friday, 04 August, 2017 - 08:54 am:   Edit PostDelete PostView Post/Check IP

I have an annoying problem with the carburettors on the car.
When I turn on the ignition I can hear the fuel pump running, some days the float in one or other of the carb sticks resulting in fuel pouring out of the overflow / vent. This happens randomly between the front and rear carburettor.
If I turn the ignition on and immediately try to start the car the occurrence is much less, I am assuming that this is because the engine is shaking whilst turning over so the floats do not stick in the down position.
I have renewed the needle valves checked the float level so I have to assume it is a sticking float.
The fuel pump is not original but a pressure regulator has been fitted.
Can anyone shed any light on what is causing the floats to stick like this?
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David Hughes
Frequent User
Username: wedcar

Post Number: 66
Registered: 7-2004
Posted on Friday, 04 August, 2017 - 03:45 pm:   Edit PostDelete PostView Post/Check IP

Hi Mark
Couple of things to check.
First that the float is not leaking, take it out and shake it to see if there is any fuel inside.
Second, check the fibre washer on the vent has the cut outs and not a solid ring.
Other than that sounds like the neddle and seat are not seating properly.
Trust that helps.
Regards
David
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Mark Taxis
Prolific User
Username: mark_taxis

Post Number: 146
Registered: 4-2007
Posted on Friday, 04 August, 2017 - 04:16 pm:   Edit PostDelete PostView Post/Check IP

Hi David
I checked the floats they are all good, no fluids inside, the fibre washers have the correct cutouts, I did have to emery cloth the float lever arms as over the years the needles had worn a slight depression in the smooth metal, maybe I did not get it totally smooth . I most probably should look at getting new floats, everything else has been replaced.
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Norman Geeson
Unregistered guest
Posted From: 81.97.73.87
Posted on Friday, 04 August, 2017 - 07:42 pm:   Edit PostDelete PostView Post/Check IP

Mark

I believe you will find that your problem is caused by the float drop being incorrectly set up. That is the float arms are being allowed to drop right down and lock in that position.

The float arms should be restricted in drop so that they drop just enough to open the valve and NO more.

If you examine the float arm pivots you will see that they have tabs which can be bent to limit the float arm travel.

These carbs catch many people out, because they look simple, a wrong assumption. I would guess that 95% of SU carbs have the float drop incorrectly set.

All thing being equal, no dirt in the system etc I think that float arm adjustment will cure your problem. Remember just enough drop to open the valve fully and no more.

(Message approved by david_gore)
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Mark Taxis
Prolific User
Username: mark_taxis

Post Number: 147
Registered: 4-2007
Posted on Saturday, 05 August, 2017 - 08:16 pm:   Edit PostDelete PostView Post/Check IP

Norman
I think you have hit the nail on the head, when I was checking the floats I noticed that if the float was allowed to drop too far it did stick, I assumed that this was caused by the slight crater in the arm where the needle sat, hence my emery clothing to remove the crater. I did not realise that the tab was there to limit the float drop.
Many thanks, yet another learning curve! :-)
Many thanks,

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