Carburettors: best left to the past or a bygone hero?
Discussion
Carburettors. An old fashioned device and with every car on sale having fuel injection, what are your opinions on it? Would you buy a new car with carbs? Past memories of cars with carbs?
NASCAR, not one of Britain’s most loved sports. Redneck paradise. Here is a 358 c.i small block racing engine with carbs! Just listen to that sound!
https://m.youtube.com/watch?v=qbi2ySdfj44
And, a 2017 racing engine with electronic fuel injection.
https://youtu.be/9g7mT51oyUc
Now, this is not the best comparison so what are cars that you miss that had carbs?
NASCAR, not one of Britain’s most loved sports. Redneck paradise. Here is a 358 c.i small block racing engine with carbs! Just listen to that sound!
https://m.youtube.com/watch?v=qbi2ySdfj44
And, a 2017 racing engine with electronic fuel injection.
https://youtu.be/9g7mT51oyUc
Now, this is not the best comparison so what are cars that you miss that had carbs?
kambites said:
In a "fun" car I'd rather have carbs than EFI. Throttle response tends to be better; they make a nice noise; and I quite enjoy fiddling with them.
On a daily driver, no chance.
The response needn't be worse if the EFI is designed/programmed properly and could be better, there is some discussion here.On a daily driver, no chance.
https://www.highpowermedia.com/blog/2900/wall-wett...
To a modern processor the delay before you get a cylinder on an intake stroke is plenty of time to sort out acceleration fuelling, the key is going to be the manufacturer putting the development time into making it correct for the situation.
Toltec said:
The response needn't be worse if the EFI is designed/programmed properly and could be better, there is some discussion here.
Agreed, but I've yet to experience a production engine where it isn't. My (EFI, Euro-3, cable throttled) Elise is amongst the better units I've experienced but it still has an appreciable throttle delay. I measured it using a diagnostics reader and there is nearly 200ms between the throttle open being logged by the ECU and the injection system starting up (that's at middling RPM from trailing throttle, so no fueling at all, to full throttle). Edited by kambites on Friday 22 December 14:16
Not as a daily now with modern engine management but I love everything about this - https://www.youtube.com/watch?v=CE_v_AWwUl0
Love carbs.
https://youtu.be/qdEub8xad2M
Our mini when we first put twin SU on it. Crap video but you get the idea. All about that induction sound.
https://youtu.be/qdEub8xad2M
Our mini when we first put twin SU on it. Crap video but you get the idea. All about that induction sound.
They certainly sound better, but the 'throttle response' is usually something of a red herring. Set up an EFI system (or open throttle bodies!) for performance, with no regard for emissions rules, and you can get an equally snappy response. And not all carbs were Weber 44s: SU carbs have a relatively 'soft' response due to the way they work, and many progressive dual-choke carbs have pretty unremarkable pick-up, especially if tuned for economy and refinement.
But I do enjoy the added 'drama'. My MG Midget was on twin SUs with 'pancake' air filters and no centre silencer and was tuned a couple of 'flats' on the rich side for some added poke, so you had some lovely induction roar on acceleration, plus some spitting and popping on the overrun. The soft hiss of the dual-choke Solex on my 2CV is part of the symphony of air-cooled noises it makes and part of its charm. The Alfasud would not be as characterful without the gurgling noise of the twin Delortos, or the little bark they make on gear changes. An old Corvette or a Jensen Interceptor only sounds and feels 'right' with a Carter or an Edelbrock dual-double jet tipping fuel into a big V8 by the bucketload. Playing with the mixture (and ignition advance) levers to keep the engine sweet was a big reason why the 1931 Morris Eight was one of the most involving and challenging cars I've ever driven.
I've always found carbs pretty reliable, so long as they're not a) Zenith-Strombergs with those stupid rubber diaphragms or b) burdened with auto-chokes, anti-run-on valves and other stuff from the technology's last gasp. An SU carburettor is beautiful in its simplicity, and those and traditional fixed-jets like Solexes and Webers are pretty much 'fit and forget' so long as they're in good condition and properly tuned. By contrast I still flinch at the memory of rebuilding the knackered Pierburg carb on my Mk2 VW Golf, with all the perished vacuum diaphragsm and hoses, but at least it ran like a dream when it was done (but there was a carb engine with a fuzzy throttle response. But generally I'd rather rebuild a dozen carburettors than sort out one knackered Bosch K-Jetronic or Lucas P/I system! But those are just as ancient history as carbs now.
Most of the 'I got into my car in the morning and it didn't start' problems with old cars are ignition related rather than carburettor. My MG had electronic ignition and started up and idled like an EFI car so long as you had roughly the right amount of choke on it.
It's like CDs versus LPs. The CD/EFI is crisp, clear, clean, reliable and technically accurate and proficient but a little soulless. The LP/carburettor is analogue and imperfect but more dramatic and somehow more involving. Pulling out the choke to just the right point and squeezing the accelerator 'just so' is like pulling the tonearm and dropping it onto the record at exactly the right place. It's a tangiable start of the experience.
But I do enjoy the added 'drama'. My MG Midget was on twin SUs with 'pancake' air filters and no centre silencer and was tuned a couple of 'flats' on the rich side for some added poke, so you had some lovely induction roar on acceleration, plus some spitting and popping on the overrun. The soft hiss of the dual-choke Solex on my 2CV is part of the symphony of air-cooled noises it makes and part of its charm. The Alfasud would not be as characterful without the gurgling noise of the twin Delortos, or the little bark they make on gear changes. An old Corvette or a Jensen Interceptor only sounds and feels 'right' with a Carter or an Edelbrock dual-double jet tipping fuel into a big V8 by the bucketload. Playing with the mixture (and ignition advance) levers to keep the engine sweet was a big reason why the 1931 Morris Eight was one of the most involving and challenging cars I've ever driven.
I've always found carbs pretty reliable, so long as they're not a) Zenith-Strombergs with those stupid rubber diaphragms or b) burdened with auto-chokes, anti-run-on valves and other stuff from the technology's last gasp. An SU carburettor is beautiful in its simplicity, and those and traditional fixed-jets like Solexes and Webers are pretty much 'fit and forget' so long as they're in good condition and properly tuned. By contrast I still flinch at the memory of rebuilding the knackered Pierburg carb on my Mk2 VW Golf, with all the perished vacuum diaphragsm and hoses, but at least it ran like a dream when it was done (but there was a carb engine with a fuzzy throttle response. But generally I'd rather rebuild a dozen carburettors than sort out one knackered Bosch K-Jetronic or Lucas P/I system! But those are just as ancient history as carbs now.
Most of the 'I got into my car in the morning and it didn't start' problems with old cars are ignition related rather than carburettor. My MG had electronic ignition and started up and idled like an EFI car so long as you had roughly the right amount of choke on it.
It's like CDs versus LPs. The CD/EFI is crisp, clear, clean, reliable and technically accurate and proficient but a little soulless. The LP/carburettor is analogue and imperfect but more dramatic and somehow more involving. Pulling out the choke to just the right point and squeezing the accelerator 'just so' is like pulling the tonearm and dropping it onto the record at exactly the right place. It's a tangiable start of the experience.
2xChevrons said:
They certainly sound better, but the 'throttle response' is usually something of a red herring. Set up an EFI system (or open throttle bodies!) for performance, with no regard for emissions rules, and you can get an equally snappy response. And not all carbs were Weber 44s: SU carbs have a relatively 'soft' response due to the way they work, and many progressive dual-choke carbs have pretty unremarkable pick-up, especially if tuned for economy and refinement.
The twin SUs on my MGB were vastly better than my Elise in terms of response.I agree it's not EFI itself which is to blame though. Obviously a simple embedded system can respond far faster than a human can perceive, they are just programmed not to.
kambites said:
The twin SUs on my MGB were vastly better than my Elise in terms of response.
I was being slightly unfair on the old Skinners Union. SUs generally have very good low- and mid-range response because they are (theoretically) always operating at an ideal venturi size for any condition. My Midget had a spot at 2700-3000rpm where the throttle was almost too fierce, which I think was also due to the programmed advance curve in the electronic ignition. But an SU doesn't have an accelerator pump, so gets less responsive as engine load, engine speed speed and throttle position increase. You can do very good things with them but even the BMC works MGs went to a Weber for track racing because they give better response at the ragged edge. tejr said:
Aren't carbs quite laggy? i only really drove one car with a carb. Everything else has been fuel injected.
They shouldn't be. If they're badly-tuned, the internals are worn and leaking, or the factory tune is focussed on economy they can be, but most of them give a very immediate response, and usually much more linear and 'natural' feel than a modern EFI system where you are requesting a throttle input rather than instructing one. You get exceptions. My aforementioned Mk2 Golf was very laggy at certain speed/gear/throttle combinations but that was because, like an EFI system, you often weren't controlling the throttle directly, but opening vacuum valves to push or pull linkages and doohickies to adjust the fuelling for you.
A modern EFI that isn't subject to being deliberately set up with the fun-killing type of stuff (damped out throttle response and so on) for emissions reasons etc should be better in every way than a carb, save for the "fix it with a mallet" factor and ability to mess about with them with basic hand tools.
The other side of the coin being some carbs feel like you need to mess with them quite a bit to keep everything happy.
The other side of the coin being some carbs feel like you need to mess with them quite a bit to keep everything happy.
InitialDave said:
A modern EFI that isn't subject to being deliberately set up with the fun-killing type of stuff (damped out throttle response and so on) for emissions reasons etc should be better in every way than a carb
Does such a thing exist though, at least without modifications? I've certainly never experienced such a thing on a road car.I threw a Quick Fuel Technology 780cfm HR-Series carb on one of my cars before I sold it. Beautiful piece of kit; all aluminium, tumble polished, four-corner idle adjustment, the works – although biased more for street driving than outright performance (among other things, it was a vacuum secondary carb).
Regardless, it was a superb bit of kit. The engine caught seemingly the first time a cylinder got a spark, it idled like a champ, restarted as soon as you touched the key when hot and the throttle response was remarkable.
Just depends on what you've got, how well it's dialled in and if everything else – vacuum, crankcase ventilation, ignition – is in good order. I had a P6 many moons ago with a rebuilt 3.5 on twin SUs and the thing drove better than any fuel-injected 3.5 I've encountered.
Hot start: https://youtu.be/tMZAYhL0If8
Would I have them on my daily driver? Well, I used to (on most of them, in fact) but these days I've moved to more modern turbocharged stuff, so they're not an option. I'd always rather have EFI than a blow-through or draw-through set-up anyway. Your engine will only run really lean once, after all...
Regardless, it was a superb bit of kit. The engine caught seemingly the first time a cylinder got a spark, it idled like a champ, restarted as soon as you touched the key when hot and the throttle response was remarkable.
Just depends on what you've got, how well it's dialled in and if everything else – vacuum, crankcase ventilation, ignition – is in good order. I had a P6 many moons ago with a rebuilt 3.5 on twin SUs and the thing drove better than any fuel-injected 3.5 I've encountered.
Hot start: https://youtu.be/tMZAYhL0If8
Would I have them on my daily driver? Well, I used to (on most of them, in fact) but these days I've moved to more modern turbocharged stuff, so they're not an option. I'd always rather have EFI than a blow-through or draw-through set-up anyway. Your engine will only run really lean once, after all...
Edited by Lewis Kingston on Friday 22 December 15:33
My Cosworth 1340 Lotus 7 with twin 40 DCOE's, my '65 1275 Cooper S with twin SU's, my 420G with triple SU's and my MGBGT V8 which had twin SU's..... Still have my old '72 B roadster which has twin SU's. I've bought the kit to rebuild them but not got round to it yet....
The 7 used to spit flames out the webers... happy days
The 7 used to spit flames out the webers... happy days
Lewis Kingston said:
Regardless, it was a superb bit of kit. The engine caught seemingly the first time a cylinder got a spark, it idled like a champ, restarted as soon as you touched the key when hot and the throttle response was remarkable.
That's what my MG was like once I'd rebuilt the (very worn and wobbly) SUs and then had them tuned and balanced by a pro, plus the electronic ignition. With 3/4 choke it would run on all four within a single revolution of the starter (you could basically flick the key like it was a push-button) and idle at a smooth 1200rpm. You could drive it away immediately and it would pull cleanly even when cold. You could knock the choke to 1/4 after about a minute and put it in as soon the temperature gauge left the Cold arc. When it was warm it would idle at a steady 750rpm with an evenness that shamed my friend's VW Scirocco on Jetronic, although the Midget did tend to fowl its plugs if left idling for too long. But it was a 1.5-litre engine producing only 65 horsepower and it did about 28 to the gallon. And I know that's partly due to the shoddy design of the Triumph OHV four-pot but when you start looking at the numbers you see the downsides of carbs.
kambites said:
Does such a thing exist though, at least without modifications? I've certainly never experienced such a thing on a road car.
My kit car runs on a Megasquirt ecu, I intend to do some throttle response tests and tuning on it at some point, but there are plenty of other things I need to do first unfortunately.Gassing Station | General Gassing | Top of Page | What's New | My Stuff