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Ohm's Classic Car Topic


so you think

carbs -> throttle valve + >3jets + extrafuel pump + fuel bowl+ fuel float + mechanical linkages within the carb + mechanical linkages around the carb + vacuum control stuff + all sorts of needles

is simpler than

injection - > throttle valve + injectors + sensors

please explain to me how it is so…

there’s also a reason they started using fuel injection systems on planes in world war II.


All these pictures of complicated carburettors… I absolutely must join in.


You just had to whip out your massive pen- graph didn’t you :joy:


I get PTSD every time the 2CV has a hiccup. I have had plenty enough of carb issues to last me a lifetime.

You may think you know how the carburettor works; you’ve studied diagrams, watched training videos, and you’re confident you understand it. You don’t. The carburettor is the product of 40% engineering, 10% prayer and 50% absolute witchcraft.

As mentioned above my 2CV (and friends Ami 8) was an absolute nightmare, and it has one of the simplest carbs going. Both cars developed running issues that couldn’t be traced even by people with many many years of experience of 2CVs. Rebuilding them, ultrasonic cleaning, checking for air leaks, even chasing faults round the ignition system, both cars were only sorted by replacing the carburettor. It only has an idle mixture adjustment, a throttle stop screw and a screw to adjust the closed position of the secondary butterfly. The jets alone control the running mixtures. The fault must have been one of the areas I listed above, but nobody could find it in either case.

By the time you’d have read this far, a computer would have probably told you Misfire Cylinder 3 and you’d have found a knackered injector.

If the above makes no sense, it is early and I’m ill and trying to talk about carbs is a bad idea.

Oh yeah, it’s hard to miss coolant peeing out of the side of your engine, haha.


there’s also a reason they started using fuel injection systems on planes in world war II.

The reason they started using Fuel injection in planes is so that they could use turbos and superchargers not for simplicity I’m pretty sure.

You may think you know how the carburettor works; you’ve studied
diagrams, watched training videos, and you’re confident you understand
it. You don’t.

I never said I completely understood it, just the basic concept behind it, that said I had no idea that so many mechanics are a bit clueless when it comes to them as if I ever got a classic car that’s how I’d have pretty much all maintenance done for it because obviously I wouldn’t trust myself to even try work on it, as I even stated before I wouldn’t even trust myself to drive a classic


there you go running off again

the british spitfire engine, the Merlin is a supercharged Carburettor engine… not simplicity for sure.

but 2 things for sure. economy and negative G forces.

economy because those things are thirsty, and needs to cover a certain amount of range.
negative G forces, what happens if you run a carb upside down? they don’t work.


The R-2800 Double Wasp has a thing to say.

First, they came Super Charged, and Turbocharged, and only used one massive carburetor

But then again, us Americans did like to make big engines.


oh nice. i was looking for a video of it after i read that


That wasn’t meant as an attack on your knowledge, it was supposed to be read in an epic movie monologue voice. You do not know the carburettor, but it knows you.


I’m not saying its impossible for a Carburated to have forced induction, but it also isn’t ideal, plane engines are known for needing frequent maintenance and I can assume that it’s much more so for ones with forced induction, they made the switch to fuel injection to probably alleviate those problems as well as the reasons koolkei listed.


The Germans were the only ones using injected aero engines in WW2, the Allies used carbs on nearly all engines.
You put the carb BEFORE the compressor, no trouble. (-ish)


The russians used injected stuff as well, including mechanical DFI in the ash82 used in the la7 and la5fn.

But in the end mechanical injection isnt much better than carbs when it comes to simplicity. Main reasons why some ww2 planes use fuel injection was, as said earlier, fuel economy but also power.

The negative g force issues can be fixed by using a pressure carburetor instead of a float type, like on the later merlins.

Also, pretty much all engines used in combat aircraft during the second half of the war had forced induction.


it’s simple

carbs require constant tuning and jet changes to suit different climates or area above sea level etc to keep the A/F ratio around 13-12:1 this must be done by a actual person and the carb cannot tell how much fuel is being burnt after exiting the combustion chamber.
A efi system will constantly do this tuning on the fly via the ecu thanks to an oxygen sensor in the exhaust reading out a air/fuel ratio at all time at all revs. So where efi becomes easier is the fact that it self tunes to suit different climates etc as the engine is being used and does not require changes to injectors of pump pressure.

mechanical injection cannot self tune also requiring constant tuning of the pump pressure and injector sizes to suit conditions (just like having to change jets in a carb), also mech inj does not like operating in anything but 100% throttle. great for drag and circle track cars not great for cars that need to idle in city conditions or war planes that require constant throttle adjustments.


Look up the Bosch K-Jetronic mechanical injection. Worked nearly perfecly in all situations.
Was in use for 20 years, the late models even had Lambda probes, therby compatible with Catalythic converters.

Do not think that Mech injetion is only 'merican Hilborn crap.

Lucas also had a really good system.


I’m back after long hiatus on this topic with a new question: any countries that fender (bonnet/hood-mounted) mirrors are illegal (reasons why illegal are optional, it can be either assumptions or facts)?

Here are the fender mirrors reference that I’m discussing (photo taken in Thailand, my country)
(Note: those cars are restored, but the fender mirrors are likely an aftermarket mirrors, due to the export (non-Japanese) markets usually received standard door mirrors).

Note: Thailand (my country) allows both fender and door mirrors, although fender mirrors are common in the past (before 1990s), particularly pickups and taxis.


They aren’t directly illegal in Quebec, but since mirrors need to adjustable from inside the cabin, it very often makes them illegal.

And from random searches on the interwebs, the same law seems to exist in many other jurisdictions.


Today (6/8/2017) is my birthday, and I’m turned 21 on this year, so I made the announcement in this topic.


Happy birthday!