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MG Midget and Sprite Technical - Weber 45 Starting

I've recently purchased a Lenham Le Mans replica based on a 68 midget with a Mamba motorsport engine and 45 Weber carbs, but its a pain to start.

I believe these carbs are not the best starters, is this normal and any better in summer?

No choke used and 4 or 5 pumps of accelerator and the engine takes a good few attempts to fire and any touch of the accelerator whilst the engine starts to rumble into life and it immediately cuts out.

Is this normal with Weber 45 DCOE carbs?

Tim
Tim Lynam

DCOE and DHLA carbs don't have chokes they have mixture enrichment devices, I know real men don't use them but I connected mine and it made starting much easier especially in the winter.
David Billington

Like David I connected mine and it does help but I found there is a bit of trial and error required regarding how much you use.

Trev
T Mason

Trev,

Like many things on older cars you're the ECU and have to learn what makes the car happy. When I first fitted a lightened flywheel I initially stalled the engine a lot but quickly adapted and no further problems.

IIRC the enrichment device may not be fitted or may have been blanked which is common on racers AIUI as waiting for it to warm up and run properly isn't so much of an issue. All my DHLAs were from road going Alfa Romeos and had them fitted as standard where starting easily and driving off quickly is a little luxury feature.
David Billington

4-5 pumps would normally flood the engine, just what you don't need with a (cold) engine to wash the bores out.
I'd be connecting the choke cable and give it full choke , give it a little sqirt like as in half a throttle jab just to wet it then start it with the full choke-no throttle--the choke (enrichener) on the weber will give it enough speed and mixture to keep running.
If you have the correct idle jets in it you won't need it to be choked for very long, then it'll run fine without any choke.

willy
William Revit

Willy, good point about idle jets. I think Webers are misunderstood by a lot of people in that, because racers tend to use them they are all about top end powder, where in fact because of all the variable choke tubes and jets, you can get them to run well throughout the range.

I have a good book about them but cant remember what its called without digging it out and I think it is well worth understanding how they work to get the best out of them.

Trev
T Mason

You say 45 Weber carbs so does it have split twins? There is an assumption it is jetted correctly.

Ideally you need to know what size pump jets are fitted and what the bleed back is.

My experience is that the engine should fire first time even in below zero degrees cold weather. However, the number of full throttle depressions (pumps) which need to be quite rapid, varies according to the temperature.

I don't think 4 or 5 pumps are enough but engines vary (an engine with the aluminium Pierce manifold seems to like 2-3 more pumps than the iron head does).

Assuming your engine has an iron head I would give it 8-10 pumps in winter weather and 10-12 pumps if the temperature is around freezing (after several weeks of not having been run and on a cold day the engine in my car, with the pierce head, started first time on 14 pumps).

In the summer I would try 6 pumps and more or less depending on the actual temperature (hot or cold day).

A failed first start can tricky and I generally use less pumps on the re-start (though note I might have used 12 so might try 8 or 9 on the re-start).

Once the engine has started be gentle at first on the throttle until it picks up nicely.

For a hot re-start - no pumps but a partially open throttle.

I have never used the cold start device but it was made by Weber for a reason.



Daniel

Thanks for all the helpful advice.

As per the photo the fuel enrichment device is fitted, I’d been advised by the previous owner not to use it.
After four pumps on the throttle and the enrichment device opened the car started first time. Unsure whether it’s the weather being a good 10 degrees warmer than previous days or using the enrichment device, but it definitely helped the starting.

Good to hear other owners tips and their previous findings but looks like each Weber setup has its own preferences for start up.



Tim Lynam

Strange that the cold start device helped with a cold start---lol
As per Trev the idle jets are VERY important part of the setup----I'd be very interested to know how far(how many turns) your idle mixture screws are set at from right in.
William Revit

Willy, yes very strange how the cold start has helped! Only being used to SU's and Stromberg carbs when the previous owner said don't use, I listened.

As for checking jets etc I'm leaving them alone until its had its first track outing or two to see how the car performs, so far after a couple of short trips on the road it appears to come to life very nicely once you put your foot down, but never realised how noisy a straight cut gearbox is especially with no carpets etc.
Tim Lynam

Ah-The straight cut gear set---a good incentive to drive fast and stay in 4th gear eh-
I'd be real interested to know how far the idle mixture screws are set out at--If you had a screwdriver and counted the exact amount to screw one in then you can put it back exactly where it is.--should be somewhere between 7/8 of a turn and 1 1/4 turns out from 0
Why I'm asking is it's a bit of a tell tale as to what idle jetting it has--which in turn effects cold start and slow running.
William Revit

Probably worth checking that the idle mixture screws are free and the tip hasn't jammed and broken off, not an uncommon occurrence AIUI as the needles are quite a small diameter and a fine taper. A mate tracked down an issue with his 45 DCOE to one or both having broken off so they were replaced after the broken bit was removed from the carb body.
David Billington

The cars had its first introduction to the Curborough Sprint Course today and after being sat outside on the trailer for a couple of days in the cold and rain, it thankfully burst into life at first attempt with the help of the carb mixture enrichment device and later performed really well.

Still a few jobs to sort before the sprint season starts but will check the idle mixture screws but now happy the Weber is performing well.


Tim Lynam

That is a fine looking motor car--

TIP-
Just an observation----Using that style of tie down straps, and having a straight cut gearbox as well--It's very important to make sure you leave the gearbox OUT of gear when trailering otherwise it'll pluck teeth off the gears with the rocking movement of the car.
Cheers
willy
William Revit

Cheers Willy, tip appreciated, I never place in gear when on the trailer but hadn't thought about it being more important with a straight cut gearbox, always good to be aware.

Regarding tie down straps I had tried the more modern type which run over the top half of the tyre, but on standard Midget tyres they were nowhere near as secure as the wrap around type.
Tim Lynam

Great looking Lenham coupe Tim!
whats upfront, also Lenham?
Please more photo's of this wonderfull car please
A de Best

Tim
Just in case I've confused things.
I'm not saying to change where your mixture screws are set to---more an interest in where they're set at.
If it's had it's idle mixture set up for best idle, then that setting will be a telltale as to if the idle jets are close to correct or not.

if it's going good there'd be no need to change any jetting, it's just a sticky beak thing from me to see where they're set at---You only need to check one really then put it back where it was--
cheers
willy
William Revit

Arie, a couple more photos, the engine is a 1398cc based on I believe a Marina bottom half A Series engine produced by Mamba Motorsports with a Frontline front suspension, the guy that built the car did a cracking job and the underside of the car looks as good as the outside.







Tim Lynam

This thread was discussed between 21/02/2026 and 04/03/2026

MG Midget and Sprite Technical index

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