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MG Midget and Sprite Technical - Float chamber - Flooding

Good afternoon,

As mentioned on Nigel thread, I experience some strange issue with my float chambers...

The car has misfiring/rough running at around 4 000rpm since some weeks, and I am trying to correct this. The other day, coming back after a 20min/10miles drive, I kept the engine ON and lift the bonnet: everything is fine at idle, and when I accelerate the engine, the back float chamber got flooded !
I "had no time" to investigate more at that time (big mistake!) and tried again today: couldn't get the flood to appear again...

Anyway, I disassemble my both float chamber. It is written AUD 9203 on the one I have issue with. I can't see any leak on the gasket, floating bowl is empty, and I can't "blow in" when the floating bowl is on the needle...

Everything looks alright... Any idea what I should check/do ?
Also, what would be the symptom while driving of a flooding chamber ?

Should have disassemble when I saw the issue :( Thanks !





CH Hamon

I went a bit further down the road...
What you think ? :)




CH Hamon

Cedric,

now it's all apart, time to get a repair kit.
Something like the first image. The second image shows how mine looked compared to the originals.
Yours look like they need replacing and could be sticking occasionally, hence it being an intermittent type of fault.




Jeremy MkIII

Is AUD 9203 on both tops?

I'm not surprised it's the rear you're having trouble with, it was way out, it might not be the only problem to the rear carb (or linkage).

What did you use to remove the brass seat as the shiny part of it suggests recent damage, the correct size tools need to be used - and non Jean-Luc les méthodes.
Nigel Atkins

"Yours look like they need replacing and could be sticking occasionally, hence it being an intermittent type of fault."
> I was hoping it is just "run in" and some sandpaper would do the trick :P So the cute old lady will need some more of my money then :p All my seals are recent, from when I cleaned the carbs. But my jets look old... Did you buy your kit on Burlen ? The seats and valves are already £20 for the two carbs...

"What did you use to remove the brass seat as the shiny part of it suggests recent damage, the correct size tools need to be used - and non Jean-Luc les méthodes."
> I did the marks, obviously :D The float axle was marked and I was afraid to force too much to remove it, so I tried to remove the seat with the float in place.... Hum, had to change my mind few minutes later ;) Second one is mint :)
CH Hamon

And, another question: is it "normal" that I can't adjust the height ? It is "by design" or the one "with shime to adjust", or it is missing a part ?
CH Hamon

I found 3 different versions:
- "almost genuine" : http://www.minispares.com/product/classic/WZX1100A.aspx
- Uprated 1 : http://www.minispares.com/product/Classic/CA90.aspx
- Uprated 2 : https://www.moss-europe.co.uk/grose-jet-gac9201x.html

Any recommendation what to go for ? :)
CH Hamon

Looked like you had used a hammer and chisel, with the chisel actually being a screwdriver with chipped tip, from being used as a chisel.

Brass is relatively soft so more easily damaged or broken.

What shim on what and where?

Is AUD 9203 on both tops?
Nigel Atkins

Nigel some valve bodies have a "ring" machined round the end about 3/16" down - it just tak3es the edges of the hexagon off - don't know why, could be an identification mark.
Chris at Octarine Services

Cedric,
I used just the standard ones as shown in your first link. The originals had lasted for 25 years and the replacements are coming up for 12 years old and are still going strong (that's tempting fate).

Jeremy MkIII

Right, I see what you mean, sorry no idea.

Is AUD 9203 on both fuel chamber lids?

ETA: make sure you clean the insides of the fuel chamber lids with the needles and seats out and clean the insides of the fuel chambers thoroughly (and gently) too.
Nigel Atkins

Cedric

Useful source of SU spares, including rebuild kits, as well as technical imformation is direct from the manufacturer
http://sucarb.co.uk (find rebuild kits using the vehicle search function, noting what numbers you have versus what is listed and what is in your Driver's Handbook)

Worth rebuilding the carbs including cleaning. Dirt blocking the float valves can cause fuel overflowing from the float bowels. Can check the float valves when disassembled by gently blowing through them and then raising and lowering the float to see if air goes through then gets shut off at the high point of the float.

Thanks
Mike
M Wood

Cedric, stick to genuine. We have found much higher rates of problems with aftermarket.

Size (of the oriface) is important, larger valves are more sensitive to fuel pressure. There are 3 sizes in the Burlen range depending on engine size. Our cars take the smallest, while many of the aftermarket valves only come in a larger size.

And speaking of fuel pressure, what pump do you have? Some aftermarket pumps put out more pressure, up to twice as much, and result in fuel bleed past the valve.

Re your question on lack of adjustment, with new valve, pivot and float the height is always spot-on. Or shall I say I have yet to find one that doesn't. Most of the time the float is OK unless the eyes through which the pin fits are worn. When this happens it can also be a source of fuel bleed.
Paul Walbran

Thanks for your feedbacks.

"My" ears and axles are pretty worn, but without being broken: is it so sensitive ? Should I go for this then ? http://sucarb.co.uk/float-chambers-spares/floats/hs-floats/hs-stayup-float-kit-hs2-hs4-hs6-small-bore-needle-valve.html
£50, before delivery and without the axles... I feel like I bought a Bugatti now ! :p

Nigel, one is written AUD2277 and the other one AUD2276 under the lid
CH Hamon

Also, I have to admit that I don't understand which one to buy, if I go only for the valve+seat... Paul, you said to go for the smallest one, so i should take the 1100 ? To what this size correspond to ?

On internet, where information is sadly not accurate, they say that both 0.070 and 0.096 fits HS2... I don't really get it. And I am also more and more reluctant to buy the same as I have, as you never know who and how those parts arrived on your car....

Thanks !

CH Hamon

Can't really say that is cheap... Hopefully, it will not need to be open before my grandson owns it ! (if I ever get one :P)

CH Hamon

ETA: Oh, too late (struggling with SU site) - but info might be helpful to others and I ask about lids Cedric.

Cedric,
I am not Paul but here are my answers - and questions - I too find the SU site difficult to understand and navigate, not enough explanations and cross-referencing and interlinking.

If your floats are worn yes replace them.

If your pins (axles?) are worn then my guess is you may need minor adjustment.

You can get replacement pins AUC 1152.

Paul put our cars take the smaller size. 0.070" is the smaller size, plus the information below from the internet. I guess the measurement is internal of the brass seat, you can check I expect.

MGOC Spares - 61 - Needle and seat WZX1100 [61] - https://www.mgocspares.co.uk/acatalog/MGOC_SPARES_1275_129.html

Moss - PART NUMBER: WZX1101A
https://www.moss-europe.co.uk/needle-valve-seat-kit-wzx1101a.html?assoc=419340

SU site - Part Number: VZX 1100 Description: Needle & Seat Kit. Viton Tip 0.070" Spring Loaded
(Note: WZX 1100 Now VZX 1100)
http://sucarb.co.uk/float-chambers-spares/needle-valve-kits/standard-needle-valves/needle-seat-kit-viton-tip-0-070in-spring-loaded.html

I have no idea if your carbs are original but it does not really matter as long as they are suitable.

Are you float chamber lids as photos below?





Nigel Atkins

sorry, flat out all day....
Yes, VZX1100 is the one. Get only from SU, some other suppliers have similar looking but aftermarket versions. This is one time where genuine is important.

Float pins AUC1152 as Nigel says. Yes they are that sensitive and the pins are cheap.

Float, see how loose the unworn bit of the old pin is in the float eyes. Should be a neat fit without bring tight. I'm not convinced on the need for the dtay-uo float. Never had issues with the original WZX1300.
Paul Walbran

Cedric,
new or old parts it is very important that the innards of the float chambers and lids are free of debris.

If the rubber hose that supplies the carbs is old, or piss-poor quality newer stuff, then now is the time to replace it as it could now or later be breaking down internally unseen. I favour a (clean) fuel filter too in the engine bay, not only filters but also serves as a very quick visual check that fuel has made it that far at least.

You know I will say it so I will put it now - previously you were farting and fiddling about with reprofiling the carbs to try to gain extra horsepower but seem to have neglected the basic maintenance that you are carrying out now (did you not clean these items then). You put the cart before the horse by not starting with maintenance before (esoteric) tuning. You can not progress to tuning until you have fully finished boring, basic, unsexy service and maintenance.
Nigel Atkins

Thanks both for the part numbers ! I was confused with all those references you can find... W or V, 1100 or 1101, all fitting HS2 carbs...

I did go for the StayUp thing, as I checked what you advises Paul, and definitely I have play between the axle/pin and the float, of about 1mm. Both are functional, but worn. Price of 2 floats + 2 valve/seats are the price of the StayUp thing, so I decided to give it a go. And they say the float can't sink...I am happy they didn't call the system Titanic !

Nigel, they almost look like this, instead that the front lid has the two pipe with a 90* angle from each other.


CH Hamon

Cedric,
that is good about the lid having a different angle, it makes more sense. The AUD 2276/7 were difficult to track down and the SU site is not as helpful as it could be.

4mm play sounds a lot to me but I might be misunderstanding.

You have no response to my other post then(?) - non.

:)
Nigel Atkins

Busy day :p

CH Hamon

Expensive (IMHO), but hopefully will stay in place for ages ! Valves should not wear and floats should not sink... Time will tell !
(crème brûlée batch 2 was much nicer too :p)
Have a good weekend end guys, thanks for advises !




CH Hamon

Cedric, you're tempting us with more crème brûlée! But we have some rhubarb fool left over for tonight (our rhubarb) so that will do for now. I have to clean up my carburettors soon.
Bill Bretherton

This thread was discussed between 19/05/2020 and 23/05/2020

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