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MG Midget and Sprite Technical - Overfueling?

I was speaking to a guy yesterday at the Ace Cafe about the fact that my front mounted fuel pump in the frogeye and he was suprised that it didnt have a fuel filter king type regulator.
He emailedd me today to say

"You may find this amusing but last night I followed you from the Ace to
staples corner and I can definitely say your car is over fueling. I had to
switch off my fan to stop the fumes!!! There was no smoke or oil just
wholesome unleaded."

Although I've not worked it out, the fuel consumption does seem high to me, but I've only owned it a few months and not done a whole load of miles in it yet.
What's the view of people here?

I've attached an image of my pump.


G Lazarus

Your car should have a mechanical pump mounted on the block under the front carb. It is possible your electric pump is giving to much pressure. Is there any fuel leaking out of the float bowls?
J Bubela

I'll have to check. Not that I'm aware of.
G Lazarus

surely over fuelling can only be too rich a mixture at the carbs, and not related to fuel pressure as you haven't reported a leak. Pull a plug and take a nosey.
P Bentley

Gary,
with various classics I've had including Spridgets
whenever I've asked about the need of regulator type fuel filter even with a very large carb I've been told no, often with a wry look.

As per recent posts on rubber fuel line I'd check any modern braided rubber as you can't see if the rubber under the braiding is cracked, crazed or leaking.

I'd think your problem is more mixture, outside chance of petrol leak as well or instead.

I know most, probably including yourself, won't like this but the SU pumps wouldn't be my first choice even if it's electronic, so if they was any problems with it I'd swap it out for a different label.

Yours pump looks like it has a vent, I don't know but wonder if that could be causing the fumes, where's it vent to(?).
Nigel Atkins

Depends on the pump. The ones designed to be mounted at the back have more blow than suck. The ones designed to be mounted near the engine have more suck than blow.

My Frog has a front mounted Electric SU of the correct type (Morris Minor IIRC).

Rob
MG Moneypit

I believe that mine is Morris minor too.
G Lazarus

Is your pump fitted at the front then Gary?
Nigel Atkins

Yep.
G Lazarus

So difficult to tell when everything is so clean and tidy. :)
Nigel Atkins

It's a cross I have to bear😊
G Lazarus

Sorry I've just noticed you put in your OP that it was front mounted, doh!

Another thought, when this chap was behind you were you perhaps running on choke.
Nigel Atkins

No bit o suspect it is running a bit rich.
G Lazarus

Perhaps you need to get more air in too, clean (or replace) the (oil fill/foam?) air filters.

Pity you couldn't have got a full 36k-mile service in at the NEC. :)
Nigel Atkins

The carburettor calibration (needle and spring on the SU and jets on a Weber (all types)) control the mixture strength of the engine. A fuel regulator prevents excessive fuel pressure from causing problems which might include running rich. A standard pump doesn't need a regulator while a racing pump does.

However, unless your car's engine is producing black smoke, a lot, then it's not likely to be excessively rich. The difference in a stoichiometric air/fuel mixture of approximately 14.7:1 and a mixture setting (on an A-Series) for full power of 11:1 is quite a lot. Given most road cars will run the stoich' anything running at 11:1 will smell quite different.

A run on the rolling road with a probe up the exhaust will give a hydrocarbon reading (not quite the same thing as an air/fuel ratio) and you'll soon find out if the mixture is rich or not.

I'd say the guy was 'definitely' mistaken - in the absence of black smoke (about 5:1).

As far as a front mounted fuel pump goes it's sometimes the case, especially with a Weber carb, to have an odd misfire that goes away when the pump is relocated to the back of the car.

What does Peter Burgess say apart from come and have a run on my rollers?
Daniel

Sorry to hijack slightly,

But a mate of mine has a spitfire with a 1500 which puffs the odd plume of black smoke. Usually when he stabs the throttle, normal? I'd guess it would be but he's not so sure.

Also, i have smaller needles, a k and n air filter and full Moss GT exhaust. Will my stock pump be man enough or should i look to an electric pump? (Only ask as iv got to take it off to change the gasket).
Karl Bielby

I've read this a few times and I can't see anywhere that he says the unleaded smell is coming from the
exhaust (ie rich mix) -

so is there an overflow from the carbs (needles sticking?), or is the top of the tank properly sealed and it slops as you go round corners, leak in the rubber.....
timmyk

What Timmy said. It sounds to me like a leak, Gary. What does surprise me though, is that your own fine nose hasn't detected it.
Nick and Cherry Scoop

Karl,
as has been proven many time and in this thread I'm no expert but black smoke isn't normal or ok.

Classics can be right old bangers but most don't have to be so, it all depends on the present owner. It may (note, may) be your mate's just needs fully and properly servicing (of the whole car) then setting up and tuning and/or some parts cleaning and setting or replacing.

Your car more or less has the same engine and set up, would you be OK with yours puffing out black smoke like some old dirty diesel. As Daniel has put black smoke, excessively rich.

As for your engine driven pump being man enough and then for K&Ns, I'd have to check the Archives as I don't know/can't remember, so I'll leave that to you or another on here to answer.

Nigel Atkins

The chap did mention "fumes" rather than neat petrol and "no smoke or oil" and he did say he was following so all suggests he's referring to the back of Gay's car. So I'd have thought he'd more likily smell exhaust fumes rather than a petrol leak as such but perhaps he might have smelt both or only a petrol leak. I'm still included to think he meant he smelt a rich mixture (but not rich enough for black smoke).

We need to get this gentleman in the dock and test his witness statement, perhaps he followed another red Frogeye or the smell and fumes were coming from his own car.

Or perhaps he's a Filter King sales rep ...
Nigel Atkins

Gary
Im no expert but assuming you have SU's wouldnt over-fuelling result in petrol leaking from the over flow pipes?
Lateral thinking - maybe your car is fine and your friend has a problem with his car!

Graham
Graham V

Sounds like--well not really--start again
Smells like it might simply need the idle mixture adjusting
Does it need much choke when cold--
Also
Everyone gets used to following moderns around with all their anti pong devices working overtime and when they get to follow a real car they think they stink, but really they were all like that not so long ago

willy
William Revit

Very good Willy - simply being unaccustomed to the smell of a real car.

Karl - friends car with a puff of smoke when he stabs the throttle - shouldn't happen even on a Weber DCOE with its dedicated acceleration pump jet system when the throttle is 'stabbed', so he needs to have a look at it.
Daniel

If it is a Morris Minor pump fitted at the front then its delivery pressure is well within the tolerances of an SU carb. If I recall it has a delivery pressure of about 2psi whereas the SU can take up to 3.5psi.

You do not need a regulator although a fuel filter may be useful. I don't think the pump is the issue.

The smell as mentioned may attributed to a number of factors:
1) Fuel leak from tank or the lines or the carbs
2) Over rich mixture setting or carbs poorly adjusted
3) Choke maladjusted or sticky cable
4) Blocked air filter

Mine has a bit of a whiff at idle as we could not get an ideal needle to give power from 1/4 throttle upwards when it was set up on the rollers.
Bob Beaumont

Thanks for the excellent feedback and suggestions.
I think I need to check the richness after making sure that there are no fuel leaks and checking the air filters (I do have a nice k&n pancake filter The type with ribs and the words sprite son the cover that I can fit )
I'll report back soonish.
G Lazarus

Sorry Daniel, should have said, it's on stock twin SU's.
Karl Bielby

Off topic, G L and others interested, I have now written a set of instructions for the Rebound strap
email is rod.bowers@hotmail.com
Cheers
Rod
R W Bowers

My 1500 suffered from bad flooding after I fitted a new fuel pump (mechanical) and 'Grose' needle and seats.
I found that the new pump was overpowering the high flow Grose units. So a new set of standard needles went in. Still flooding but not as bad, Hmmmmm, so refitted the old needles and the problem disappeared. Imagine that.
Still running on these, however every now and again I can smell petrol at idle and low revs, maybe the new fuel pump is overachieving.
Cheers
Rod

R W Bowers

Karl, (Gary),
Rod makes a very good point.

You may want to pass on these links to your mate for general info and useful to yourself too.

The first link shows at the start of the vid needle and seat comparisons.

222 MG SU Carburetters: Setting the Float Height (needle & seat comparison) - http://www.youtube.com/watch?v=82YNx-RkGNI

232 MG Carburetter Needles and Seats (odd sizes) - http://www.youtube.com/watch?v=pVX_JClyeDQ

41 Matching SU Air Pistons - http://www.youtube.com/watch?v=IfU47Oqq9wA
Nigel Atkins

If you decide you need a fuel pressure regulator and the carburetion is SU be wary of Filter King regulators, they are happy with the pressures Webers need but are not really suited to 1 1/2psi recommended for SUs, we tend to use the dial-type Purolator ones and a separate filter.
Peter
Peter Burgess Tuning

Thank you Peter. Exactly what I wanted to know.
Greybeard

Cheers Nigel, i will have a watch when not in the company of the in-laws!

Interesting Peter, at what point do you know a higher fuel flow/pressure is needed? Hopefully the car will be making its way over to you at some point soon Peter, but i want as much sorted beforehand as possible!
Karl Bielby

Rod
The Grose sets aren't finished off quite as good as they used to be and I've found the ball needs a little light tap into the seat to seat them when new
I feel that they are just drilled and put in the packet now where they used to be seated in originally
After giving them a little tap they seal up nicely
willy
William Revit

If you fit Weber/s you need higher fuel pressure than for Sus. If you have a higher pressure pump than required for any carb you will have to reduce the pressure to suit the carb. Size of pump is different, basic off the shelf pumps will have enough flow for road use. The Filter King struggles to cope with 2psi or less as the spring arrangement tends to cease to be effective and can even reduce fuel flow. They are fine for 3+.

We have seen the same problem with the Grose jets Willy.

Peter
Peter Burgess Tuning

Gday willy thats very interesting, I didn't throw them away so if in the future I need replacements I can do this. Presently the old ones are Ok.
cheers
Rod
R W Bowers

Ok, so regardless of what you do with SU's, the stock pump will be fine?
Karl Bielby

Just to recap, you've got a 1979 1500 with mechanical fuel pump and you want to know if it'll be OK with "smaller needles, a k and n air filter and full Moss GT exhaust".

I'd have thought that if all components are correct and working correctly then you'd be OK

- but

- others will know better than me.

From the Archives I read (and got totally sidetracked) that a later 1500 would have a later mechanical pump with a space between it and the engine to help insulate a bit against heat so the fuel is a little cooler as it leaves the pump (details of the pump and its cleaning are in the Driver's Handbook ... of course).
Nigel Atkins

This thread was discussed between 12/04/2017 and 18/04/2017

MG Midget and Sprite Technical index

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