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MG Midget and Sprite Technical - Needle Valve Adjustment

I am having issues with too much petrol going through my carbs this I know as I can smell petrol at standstill.

In trying to resolve this I have replaced the needle valves as the previous ones where well worn with a nice ridge.

When I turn the ignition on the pump clicks away until pressure is achieved and then clicks every 1 second or so which I am sure is too often.

I then checked the float level and that seemed to be incorrect so I manufactured a fibre washer to put under the brass body that screws into the float chamber which seems to have helped.

What is the correct the method of adjusting it? If so what size fibre washers do I need to order?

Thanks In Advance

Shaun

Shaun

Shaun,
i haven't mucked around with SU's for years, but on my Stromberg set up the needle valves have a soft ali washer under them. I would be concerned about a fibre washer expanding.
cheers
Brad
Brad (Sprite IV 1380)

In that case why do they use a fibre washer as a seal on the float chamber?

Shaun

> "When I turn the ignition on the pump clicks away until pressure is achieved and then clicks every 1 second or so which I am sure is too often."

Is that with the engine running or not? If the engine isn't running then there should be no further clicks from the pump once the float chambers are full. If there is then the float valves aren't sealing. I'm not sure about washers - best consult an SU diagmar and see what should be there. I don't think you should add anything which isn't standard fit. Also note that a fuel smell is to be expected when you switch off and leave it standing. The float chamber is open to the jet and there will be some evaporation of fuel around the jet orifice when it's turned off and left standing. This can be more noticable if you park on a hill!

Ant
Ant Allen

Sorry all, it is clicking without the engine running, without a washer in place the fuel was coming out of the overflow and sitting on the top of the chamber lid. With the fibre washer in place it was curtailed and the pump stopped operating so often.

However it was short lived and is now clicking away without the engine running but I cant see any sign of overflow

Shaun

Shaun

Oh and the floats are all plastic with no way of adjusting that I can see. so putting the fibre washer in was the only option I could think of.

Ta

Shaun
Shaun

Shaun,
Have you checked that you don't have a small leak in the fuel pipe into the carb. You'd get the same click and the same petrol smell at standstill.
Gary Lazarus

Because the fuel level is below the seal.
Brad (Sprite IV 1380)

You bend the metal arm that holds the float onto the pivot arrangement. Hold the lid at 90 degrees so that the float hangs down and bend the arm until the float sits at the correct distance from the underface of the lid just as the metal link touches the plunger on the viton tipped valve thingy. This is the way to measure the correct amount of bend to put on the metal link to ensure that the float pushes the valve thingy lightly against the brass seat jobbie tubey whatsit that it resides within.

If you have either a hole in the feed line from the tank to the pump, or the union that bolts into the tank with a 'tapered olive' fitting on the end has either de-soldered or rusted then you'll find the pump ticks slowly away forever with the engine off. If you are getting ticks with the engine off and then an overflow you might have a duff seal due to damage on the viton tipped valve that sits in the carb lid or within the brass holder that you've spacered out with a washer. IIRC, the brass jobbie is a fairly tight fit in the thread but there is an alloy washer under it.

I hope this helps.

rob multi-sheds thomas

I get this from time to time on my 1066 Mk 11 and I put it down to dirt in the fuel system. Have a look in the bottom of the float chamber bowls for a nice layer of brown crud and clean it out as best you can.
I might even fit a filter in the fuel line one of these days !
M J Chapman

Rob,
well explained, i don't have a manual to hand, i have found with the Strombergs is that it takes a bit of playing around from the factory settings to get them right.
Brad (Sprite IV 1380)

Rob,
The early plastic floats are as you describe, but the later ones in my RWAs have NO metal piece; there is NO adjustment other than shimming the inlet valves.
http://www.sucarb.co.uk/ProductDetail.aspx?Id=23567
David "brass floats for me" Lieb
David Lieb

Best fit a DHLA then.
Brad (Sprite IV 1380)

Brad,

In theory the fibre washer would be fitted will not be near the petrol and is only really used as a spacer. I will check however to make sure.

Could the plastic float be worn and I should try another?

Could be as somebody else mentioned gunk in the bottom of the float chamber.

I'm going to put bolts in the end of the hoses, turn the iginition on to check and see if the pump then stops clicking and by a process of elimination identify where in the system the leak is.

Thanks for all your suggestions

Why stop at the DHLA I think it's time to go for the full K with emerald!!

Shaun

And what if there is some crud between the non return valve on the inlet port of the pump?
The pump membrane is under pressure when the pump is at rest, this pressure will slowly seep back to the tank untill the membrane relaxes enough for the contacts to make another stroke.
Alex G Matla

Is it a standard pump or a high pressure one? If the pressure is too high it will push the float and needle down against the force of the buoyancy.
rob multi-sheds thomas

Hey Shaun..........

when U replaced the needles in the carbs did U replace the seats also? (other half above the needle)

Plastic of fibre washer between the seat and lid is ok and U can use 2 if needed.

later floats are all plastic. Earlier ones have a metal tab that can be somewhat adjusted but not much.

Turn the pump on to fill the float bowls (4 sec or so) then turn off. Remove the lid and check the fuel level. ONE INCH down form the gasket face of the bowl.

Make sure no gas is leaking out the bottom of the float bowl by the small hose on the bottom.

Do check the fuel pressure ...no more than 3 psi...2.5 psi (#'s per [] inch) is best.

Do plug the fuel lines as you posed ad see if the clicking stops. About 1 klik every 5 seconds is about rite. The pump could be going away and its talking to you....but that has nothing 2 do with fuel leakage unless its too high pressure.

Have fun.
M. Who

So last night the exploration started.

1. Plugged the main feed to the carbs with a bolt. No clicking when the pump was left on.

2. Plugged petrol pipe from front carb - no clicking.

3 Took pipe of the rear carb and plugged it - no clicking.

4. no plugging still got the clicking and petrol on top of the float chamber.

Took the lid off the float chamber and petrol was an inch lower than the top. I changed out the lid for another one I had with a different float and still the same.

My conclusion and I will check tonight with a new piece of petrol pipe is that the old one to the rear carb has persished.

Shaun
Shaun

Quick update,

All

Thanks for all your help peoples, Was a perished pipe causing the issue running down the back and onto the top of the float chamber, it was a braided pipe so I could'nt see the problem.

Now fixed and the pump is behaving itself.

Cheers
Shaun
Shaun

Here's a question - why do people like braided pipes so much? This thread is a classic example of why I hate them. When the rubber is perished or split it can leak but it's all hidden by braid. I once had this exact problem on a 205. I replaced the offending hose as I saw petrol dripping off the braiding part way along. A month later it caught fire on the M40 and I never got to fix it ever again! I'm convinced it was a leak in another braided pipe which I'd not spotted.

Braiding on brake pipes is supposed to stop them expanding. I reckon that's pretty minimal though. Some say braid them for heat dissipation but that's what the exhaust heat shield is for. So is it just to make them look shiney?

Ant
Ant Allen

The plot thickens, having thought the issue was resolved, I went for a test run today and the smell of petrol wasa back, lifted the bonnet and puddle of fuel on the rear carb float chamber dripping down the side of it.

Put the old needle valve back in and problem sorted.

So I have a faulty new part which seems to becoming more common recently!!

Oh well at least I got to the bottom of it.

Heres hoping the fuel consumption will be better

Shaun
Shaun

Im with Ant on the issue of braiding on fuel lines. The slippery wires mean that the tube clamps can't do their job properly by getting a good grip on the rubber pipe. I had no end of leaks until I took all the braiding off.
David Cox

I agree, I've just replaced my leaking bling braided pipe with the original rubber type. That's why I mentioned it all the way back towards the start of this thread.
Gary Lazarus

Hi Shaun,
I came on this post a bit late. I went through all this a couple of years ago. I had a leaking rear carb with exactly the symptoms you have (had). New needle valves and still leaks. I did the fibre washer thing also as the plastic floats have no adjustment. I did find that the fuel pump was pushing out too much pressure so installed a fuel pressure regulator. After much messing about I found that the replacement needle valve was faulty also. So much for new parts!

Are you going to Lavenham on Monday?
Steve Church

Gary, I ruled out the fuel pipe because I put a bolt in the end of it and no leak. The pump also did not click with the ignition turned on so I assumed the issue was with the float chamber.

Steve, Yes both the Sprite and midget will be going on Monday to Lavenham.

Shaun
Shaun

This thread was discussed between 24/08/2009 and 29/08/2009

MG Midget and Sprite Technical index

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