Carburettor needle valves

[Steve B]

The float chambers were overflowing so I’ve replaced the valves to the viton tipped ones. I’ve started to get fuel starvation problems and have rebuilt the fuel pump with new points etc. With the fuel pipe removed from the o/s carburettor I got 1/2 pint of petrol in 10 seconds. I’ve stripped the carbs down & replaced the diaphragms but there is nothing obvious for the fuel starvation. The tank vent is clear with a new filter
My only thoughts are that the viton valves have an additional filter on top - should I remove these?
Thoughts anyone or anything else I should be looking at. Also the butterfly shafts have minimal wear

[mike@thenook]

Did you check the float valves heights are as detailed in the ROM, they may have changed with the new valves...?

[Steve B]

Both checked and were to the workshop manual level

[wilf]

Could you describe the fuel starvation symptoms?

[jbuckl]

Were the float heights adjustments made with washer (correct) or bending the tabs? (Incorrect)

the float tabs sometimes have a wear dimple.

should be flat and smooth.

[Lingen]

Hmm. Won't adjusting the float height by either method make allowance for any small "Dimples"? I am not aware of washers of varying thicknesses being available, but I agree that bending is a crude engineering solution. However, I think it is the one that B/L and Stromberg used.
Mike.

[marshman]

As Mike says no difference in either bending the "float arms" or using different thickness washers.

The original / genuine needle valve kits from Zenith usually did have several different thickness washers, usually aluminium, for adjusting the float height. The "official" Zentith Stromberg Service instructions say to bend the arm/tag or pack out with thicker washer. I have attached a scan of the service document & and a couple of pictures of a genuine needle valve pack with 3 different thickness washers (not needle valve is not for the Stag carbs but another Zenith carb.)

I don't think any "dimple" will affect anything as you check the actual float height which should take account of any wear/dimple.

valvepack1.jpg valvepack2.jpg
6P-6AK.jpg

[Steve B]

The float height was adjusted with the washers that came with the valves. With stripping everything down I did find that one of the needles was lower than the other. I’ve adjusted this and just come back from a ’spirited run’ with no problems. Thanks guys for all your input. I’ve just got to sort the tickover out now…
I also found an easy way to remove the brass advance and retard nipple. It’s easily accessible with the o/s damper removed

[Steve B]

Could you describe the fuel starvation symptoms?

It was like you were running out of fuel a bit like the inertia switch had popped up or the fuel pump needed a tap

[richardthestag]

The float chambers were overflowing so I’ve replaced the valves to the viton tipped ones. I’ve started to get fuel starvation problems and have rebuilt the fuel pump with new points etc. With the fuel pipe removed from the o/s carburettor I got 1/2 pint of petrol in 10 seconds. I’ve stripped the carbs down & replaced the diaphragms but there is nothing obvious for the fuel starvation. The tank vent is clear with a new filter
My only thoughts are that the viton valves have an additional filter on top - should I remove these?
Thoughts anyone or anything else I should be looking at. Also the butterfly shafts have minimal wear

Hi Steve

first and foremost the stromberg carb is a very simple device and certainly not something to be feared. You should be able to service and set them up for a fraction of the cost of an alternative fuelling setup that brings a whole new set of issues with it. I regularly post videos up on yootoob to show the stuff I deal with and how I get around the bodges casually thrown in my folk who know no better. https://youtube.com/playlist?list=PL...feature=shared

When I have issues with strombergs I need to run through a set series of steps to ensure that the supply of fuel and air is as intended and that there are no additional air leaks

Flooding carbs that have previously behaved is more oft than not down to the needle valve, the floats rarely sink. Needle valves wear out sometimes because cheap nasty rubbish, sometimes because grit from a dissolving 30+ year old fuel line jams them open and sometimes because something recently got changed, like a fuel pump.

I frequently (nearly every single time) find that the fuel pump is pushing too much fuel pressure. Most pumps sold for the stag as original equipment will push 4psi or more. The carbs really like between 2.5 - 3psi with the engine running. So you need to check fuel pressure and then if necessary regulate it.

If the pressure drops below 2.5psi then it may struggle to get the past the needle valve.

Do not confuse flow with pressure. electric supply to the fuel pump goes via the inertia switch on the left side of your bulkhead and behind the wiper motor. This is a safety device, bypass it by all means to test the circuit but they are dead easy to fix. A rogue connection in the circuit will show a hearty 12v feed but with zero load, if the connector / contacts in the inertia switch have gone high resistance then the voltage will drop to zero as soon as load is applied, Ohms Law. You could simply try an incandescent bulb tester on the feed wire to the pump and earth to the pump body. the light should glow as bright as if connected directly across the battery. A nice 12v 21w bulb such as indicator or reverse light is quite useful in a rear light bulb holder with a couple of wires to test circuits.The fuel pump needs to be earthed back to the body, stuff like this hidden away for decades gets ignored (out of sight out of mind) contacts start to corrode, resistance increases, voltage slightly drops (but not so you would notice) and heat is introduced which accelerates the corrosion. viscous cycle, copper over heats and starts to break down etc etc etc

Next float height, as per the ROM, measure from the base of the carb to the top of the float on the corner nearest the needle valve.. do not have the gasket fitted to the carb body. 17mm is what you are looking for.

Be sure that the float is fitted the right way up.

over the last 4 weeks alone I have had 5 Stags to deal with, all but one had a set of "refurbished" carbs fitted but not set up nor tuned.

This is a video from a stag that almost beat me with a weird carb issue https://youtu.be/Vd8ragn_9jc?feature=shared A lot on time invested to get to the bottom of this issue!

Watch if you want, root cause was pattern needles fitted for a decade that were marked B1AQ but were absolutely not!

Car ran like sh1t, i was not happy with it, customer thought it normal. I was able to transform it by fitting a decent pair of meter needles.

Lesson learned for you all is ONLY BUY CARB PARTS FROM BURLEN, buy from other suppliers if in original Burlen / Zenith / Stromberg packaging. If it isn't send it back with a cat turd in the packaging

[gbb483]

In general it shouldn't make any difference whether you adjust the float height with washers or by bending the tabs or a combination. The only real difference I can think of is that the space in the carb. body above the needle valve will be less if you don't use the washers. The filters (are they flexible?) on the Viton valves may be compromised if there is insufficient space above the valve body, so with those it may be advisable to use the washers. However, I've never seen a Viton valve in the flesh and I don't have a carb. body to hand to check the machining above the valve body.

[Steve B]

Hi Steve

first and foremost the stromberg carb is a very simple device and certainly not something to be feared. You should be able to service and set them up for a fraction of the cost of an alternative fuelling setup that brings a whole new set of issues with it. I regularly post videos up on yootoob to show the stuff I deal with and how I get around the bodges casually thrown in my folk who know no better. https://youtube.com/playlist?list=PL...feature=shared

When I have issues with strombergs I need to run through a set series of steps to ensure that the supply of fuel and air is as intended and that there are no additional air leaks

Flooding carbs that have previously behaved is more oft than not down to the needle valve, the floats rarely sink. Needle valves wear out sometimes because cheap nasty rubbish, sometimes because grit from a dissolving 30+ year old fuel line jams them open and sometimes because something recently got changed, like a fuel pump.

I frequently (nearly every single time) find that the fuel pump is pushing too much fuel pressure. Most pumps sold for the stag as original equipment will push 4psi or more. The carbs really like between 2.5 - 3psi with the engine running. So you need to check fuel pressure and then if necessary regulate it.

If the pressure drops below 2.5psi then it may struggle to get the past the needle valve.

Do not confuse flow with pressure. electric supply to the fuel pump goes via the inertia switch on the left side of your bulkhead and behind the wiper motor. This is a safety device, bypass it by all means to test the circuit but they are dead easy to fix. A rogue connection in the circuit will show a hearty 12v feed but with zero load, if the connector / contacts in the inertia switch have gone high resistance then the voltage will drop to zero as soon as load is applied, Ohms Law. You could simply try an incandescent bulb tester on the feed wire to the pump and earth to the pump body. the light should glow as bright as if connected directly across the battery. A nice 12v 21w bulb such as indicator or reverse light is quite useful in a rear light bulb holder with a couple of wires to test circuits.The fuel pump needs to be earthed back to the body, stuff like this hidden away for decades gets ignored (out of sight out of mind) contacts start to corrode, resistance increases, voltage slightly drops (but not so you would notice) and heat is introduced which accelerates the corrosion. viscous cycle, copper over heats and starts to break down etc etc etc

Next float height, as per the ROM, measure from the base of the carb to the top of the float on the corner nearest the needle valve.. do not have the gasket fitted to the carb body. 17mm is what you are looking for.

Be sure that the float is fitted the right way up.

over the last 4 weeks alone I have had 5 Stags to deal with, all but one had a set of "refurbished" carbs fitted but not set up nor tuned.

This is a video from a stag that almost beat me with a weird carb issue https://youtu.be/Vd8ragn_9jc?feature=shared A lot on time invested to get to the bottom of this issue!

Watch if you want, root cause was pattern needles fitted for a decade that were marked B1AQ but were absolutely not!

Car ran like sh1t, i was not happy with it, customer thought it normal. I was able to transform it by fitting a decent pair of meter needles.

Lesson learned for you all is ONLY BUY CARB PARTS FROM BURLEN, buy from other suppliers if in original Burlen / Zenith / Stromberg packaging. If it isn't send it back with a cat turd in the packaging

Thank you for the information all very useful I’ve just checked the packaging and the viton tipped valves are genuine Zenith from Paddocks. Also working through everything I found a slight weep from the pump banjo in the boot. With new fibre washers I seem to have cured the petrol smell in the boot so I’ll be refitting the carpet now.
Love the video which reminds me to oil the distributor weights.

[jbuckl]

As Mike says no difference in either bending the "float arms" or using different thickness washers.

The original / genuine needle valve kits from Zenith usually did have several different thickness washers, usually aluminium, for adjusting the float height. The "official" Zentith Stromberg Service instructions say to bend the arm/tag or pack out with thicker washer. I have attached a scan of the service document & and a couple of pictures of a genuine needle valve pack with 3 different thickness washers (not needle valve is not for the Stag carbs but another Zenith carb.)

I don't think any "dimple" will affect anything as you check the actual float height which should take account of any wear/dimple.

valvepack1.jpg valvepack2.jpg
6P-6AK.jpg

The dimple can affect operation…. Float moves through an arc. Dimple can interrupt smooth movement, especially with a new valve.

[marshman]

The dimple can affect operation…. Float moves through an arc. Dimple can interrupt smooth movement, especially with a new valve.

Good point, I was think more of the fuel level. It's always good practice to check the operation of the valve/float before reassembly. Connect a bit of tube and blow into it and then gently lift the float with your finger and check it shuts off the airflow with only light finger pressure and opens again when you let go - found a few needle valves that "hang up" or stick shut for a bit that way. You can usually feel any "mechanical" issues such as a "dimple" - though in reality the float level should only drop very slightly before fuel starts to flow and lifts the float again, very limited movement and as the float is almost level at that point not much of an arc to swing through.