MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG Midget and Sprite Technical - Weber 45 flooding?

yeah it's me again!
Still not got my midget running right but now have a few more symptoms.

Took her out yesterday, she started fine & ran perfectly, no problems whatsoever for about 5 minutes.
Then she started to misfire, but I had reached my destination.
I cam back to the car an hour later & again, she was running fine... for around 5 minutes. Stopped at the car wash & jetted her down.
Again, on starting, smooth running for 5 minutes until she got lumpy on me again. I limped home and she really didn't want to tick over.
Spec (if you dont know me from here already!)
1430 stage II
Weber 45, Facet pump, speed king filter/regulator.

Ive already tried:
cleaning then replacing plugs, cleaning all jets on Weber, ignition diagnostics.
The fact the misfire clears when left for a few minutes is pointing me towards fuel flooding.
Choke is not stuck on (well not from the outside anyway, and when I pull the choke, it does what it does so is working)
Never actually stripped a Weber down, is this what I'm going to need to do?




Mallorcaben

Ben.

The Weber is a brilliant carb if set up right and maintained. The old wives tale of the always going out of tune is fiction, if anything goes out of tune it's the engine itself.

My experiences with these would lead me to think in a few directions. the first is the float height and needle valve. Both these need to be set correctly, so refer to a manual (or someone on here may have more time this morning to give specifics). Next and possibly the first thing you should check is fuel pressure. No more than 3psi, 2.5 is really enough for a road car, make sure this is set correctly if not that will be the cause of your problems.

I am assuming the carb is correctly jetted and set up on this engine....

Other things to check are carb to manifold tightness (these carbs need (in most cases) to me flexibly mounted. Venturi and Choke tightness, make sure they are not loose and vibrating in their housings, this will give misfire symptoms...

Good luck and let us know.

Mark.
M T Boldry

Sorry, I didn't think that the webber had a choke which you pulled. When I had Bob's 45 installed on my car, it was just four pumps on the peddle to get it started.
Gary Lazarus

yeah Gary, a few pumps on the throttle is correct, but they do have a choke. I never use it here (in Mallorca!)
Fuel pressure is a possibility, never had a gauge to set up the filter king regulator. Been given lots of hints on here but never sure with it.

Mallorcaben

Ben,
check your pressure first, as we have said before in your previous posts, a gauge is cheap enough & regulators do go wrong.
If the pressure is Ok, then strip & clean your DCOE, buy the DHLA/DCOE carb book in the speed-pro series, it will guide you through it.
If you know some one with an ultrasonic bath, then take your carb bits to them for a proper clean.
Brad (Sprite IV 1380)

Hi Ben

I keep coming back to this... probably an old age thing:

- car goes well for 5-10 mins (when it's cold?)
- then starts to misfire like it's running rich.

Classic symptoms of choke stuck on. How are you sure the choke is not engaged in any way (externallly or internally?)?

Or possibly a sign that the float chambers are slowly filling up as the shut-off valve isn't working (too high fuel pressure, worn needle valve etc. as commented above).

Actually... if problem is either of the above, a temporary fix would be to dissconnect power from the fuel pump and drive on the excess for a min or too, until it misfires due to being overweak. Connect the pump up again for 30s and carry on...

... just needs the GF trained to recognise the symptoms; she can then be the fuel pump operator.

(Well if this worked, then you'd have narrowed down how to fix....)

A
Anthony Cutler

OK, before I buy a fuel pressure gauge, what should the pressure actually be?
You know, when I bought my Facet pump some years back, I didn't adjust the filter king pressure regulator.
Wondering if this is what has been causing my high speed misfires!
So, anyone know what the pressure should be for a Weber 45?
Mallorcaben

"So, anyone know what the pressure should be for a Weber 45?"

Ben,

Read the second post.

Charley
C R Huff

Ben,
you really should buy this book, read it, then look at your DCOE.

http://www.amazon.co.uk/Build-Power-Dellorto-Carburettors-Speedpro/dp/1903706750
Brad (Sprite IV 1380)

Ben it's odd but you don't seem to read the replies you get. Several threads back I asked which particular Facet pump you have (there are 2 types and several models of each type) and even listed a link to some pics to help you identify. Also I suggested you bypass the pressure regulator and report back. But I can't find any feedback on these points.
David (davidDOTsmithAT stonesDOTcom)

David, I've been told not to bypass the regulator with my pump, it's a high pressure one. I did read the reply you wrote but was given advice elsewhere regarding it.
At the time I looked up the model etc, can't remember offhand.
Mallorcaben

Not sure of your diagnosis, why do you think the weber is flooding???

If the weber was flooding and therefore the float valve was passing, then it would still run OK on big throttle openings but you would smell peterol like it was going out of fashion, or in the worst case with ignition on and engine not running you would fill the cylinders with neat fuel.

Potentially the problems you describe could be caused by too rich a mixture but this would not simply just happen. Some webers do have a positive enrichment device (choke) but normally if this device is fitted and the external linkage works correctly then it is pretty bullet proof internally.

If you are convinced this is a rich mixture causing this problem then check on the jet sizes and report back, although I am far from being connvinced of the problem. Could it be a lack of fuel causing the problem? something as silly as the fuel cap not being vented?

I have run webers for most of my life, still have one fitted to my MGA and I have very rarely used a pressure regulator, I use the electronic square pump without problems. Webers should be alright with anypressure between 2 PSI and 4 although I suspect increases in this pressure would be OK. However on my MGA I have the square pump and an original SU. If I run with the SU then I tend to have a weak mixture when compared to running on the electronic, I suppose with the higher pressure I must get a slightly high fuel level which would richen it up a bit.

Robert (Bob) Midget Turbo

But you don't know if the regulator is working properly or adjusted correctly.
Brad (Sprite IV 1380)

OK let's try again; what do you mean by 'high pressure'? I run a Facet gold pump in my racecar (1380, 286 cam, 36-29 head, hiratio rockers), the 45 runs just fine, and I don't use any sort of pressure regulator. Why are you not prepared to at least try it out? Failing that why don't you spend a few euros on a pressure gauge and T-piece?
David (davidDOTsmithAT stonesDOTcom)

sounds like a heat related ignition fault.

condenser.
or maybe coil.




robnrrugby

I run split weber 45's on my race car without a regulator. At set-up we checked the pressure and all was fine - can't remember the pressure - with a silver top competition Facet pump.
John Collinson

Ben - I also run without a regulator on the racer and no problems - I'll check which pump is installed. To complete the set, afaik, Oily Pete doesn't have a regulator either and it doesn't seem to slow him down...

As above, give it a go without the filter king.
Steve Collinson

ok, bypassed filter king regulator. Ran like a dream for 5 mins then missing again, especially at low revs. Wont tick over.
checked plugs, black, jet black, sooty, dry,
Cleaned plugs, started ok, but the problem cam back really quickly this time.



Mallorcaben

good - now you need that pressure gauge to reconnect the regulator and set it correctly. 3.5 psi?
David (davidDOTsmithAT stonesDOTcom)

The choke is actually a cold start device because it enriches the mixture rather than strangles the air flow. I'd disconnect it and fit a blanking plate to: save weight, remove a potential problem and because you don't need it (nor does the engine..).

Even if the cold start device was jammed open I'd expect a lot of black slow and a reduced top speed - are you getting a lot of black smoke from the exhaust.

I still think this is an ignition fault - coil, coil lead, bad wire to the LT side of the coil or whatever.
Daniel Thirteen-Twelve

* Well, I think I've ruled out the pressure thing! Also I don't think it's flooding as the plugs were not wet, just black.
* Ignition is not going to produce black, sooty plugs (is it?)
* Have cleaned the K&N, even ran without it to test. Usually black plugs mean mixure too rich, but in 14 years, I've never had to adjust the mixure on the Weber, why would it suddenly change?

Mallorcaben

Ben
you have only determind that removing the pressure regulator does not fix the problem.

if you now refit and adjust properly than you know if it has not been the fault
Onno Könemann

Daniel,
interesting you mention ignition fault...
The problem started after I had a new starter motor fitted. The only thing the mechanic touched was the dissy, which he removed to get to the starter.
When I got the car back, I was getting backfires, then she started misfiring. (this was all on a prev thread)
I assumed something in the ignition system had been damaged/moved but was told categorically that this was not the problem.
I'm not 100% sure the black plugs are causing the misfire. The car was running rich before anyway.
The weird thing is this, she runs smooth for 5 mins then starts misfiring. If the ignition was damaged, she wouldn't run smooth at all.
Onno, as regards to the fuel regulator, people have told me on here that they run similar spec without one, so I'm leaving it disconnected until I can get a gauge to measure it.
Mallorcaben

Ignition faults are often only manifest once the faulty component warms up - eg the coil. Loose connections can vary with vibration etc.

An engine can run incredibly rich and produces lots of black smoke without a single misfire.

Your engine's main problem is a misfire. You have decided that black plugs are a sympton of the problem. My opinion is that while your engine has black plugs and this may be a sympton of a carb problem it is NOT a sympton of a misfire. That's why I still maintain you have some kind of ignition or failing that an electrical fault.
Daniel Thirteen-Twelve

Are you sure it is flooding? I had an MG with the same symptoms and it turned out be some junk in the fuel line that would gradually clump up in a turn in the metal fuel line and would settle back out when the car sat for a few minutes. New fuel line- problem gone! Just a thought.
Mickey
Mickey

A misfire can give a black and sooty plug,
especially at low speed..
If the mixture fails to fire on one compression stroke , there is heaps more fuel kicking around in the chamber (especially on an A series hahaha) for the next spark event, so when it does fire it is rich. This can also emphasise the mis-firing roughness ....since the first fire after a misfire is a bigger thump.

Re-reading your original post.
'The fact the misfire clears when left for a few minutes is pointing me towards fuel flooding'

If the misfire was due to over rich mixture/flooding I'd expect some plug wetting, petrol smell in the exhaust, fluffyness, and refusal to run after a while rather than a 'misfire' that still enables you to get the car to where your going and drive it home again.

And your last post:
~~If the ignition was damaged, she wouldn't run smooth at all~~
I'm not sure that everyone would agree with you on that one, (well me and Daniel at least :).....It is quite possible to have ignition faults that only occur once things are hot.
This is what I'd do
~1 Has it got a condenser? this is the classic failure sypmtom, and they are a continuous source of entertainment, hence the alternatives.
~2 how old is the coil? either swap it or get it to misfire and pour chilled water on the coil and see if it goes away (carefully!)...

I was in Pollenca last week. Nice and hot it was to.
Rob
robnrrugby

This thread was discussed between 26/08/2009 and 04/09/2009

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.