Carburetors - I think I've learned to like them

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Nov 23, 2015
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As far as looks and sound both go, it's really hard to beat a Weber DCOE, especially when you can line up a bunch of them.

I also know MG guys who have gone broke trying to jet one correctly to behave on the street...unfortunately it's hard to get them dialed in for an engine that small, and people who do them also cite needing two of everything. The ones who have manged to get them right love them.

For smaller displacement engines, the DGV is a lot more tame and also easier to set up correctly(even though it seems to be common to modify emulsion tubes since nothing off the shelf is exactly right). The DGV doesn't look as sexy as a DCOE, but does give you a lot of the sound.

One thing for sure-tinkering with an automotive carburetor without the air filter housing on it makes you appreciate just how much air an engine can suck in especially at higher RPMs. My preferred dual SU balancing technique is to use a long hose with one end next to the throat and the other end in my ear. Even on those little bitty carbs, you hear an impressive amount of air when you "blip" the engine.
 
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Emissions, emissions , emissions. I think that about covers it.

Carburetors can be relatively clean IF they are always operated under pretty much the same conditions. Of course, that's not the case for most things, especially street cars.

By the mid-1980s, the hold-outs on carbs were using technology like feedback carbs, which usually use an O2 sensor and use the data from that to adjust the mixture on the fly. It was a band-aid when close-loop FI was a better solution, but at least up to a point it was apparently less expensive and easier to implement than going to EFI.

Even by the late 70s, carbs had gone from the friendly "adjust them on the side of the road" devices to basically not making any end-user adjustment(idle or mixture) not easily accessible.
 
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Feb 26, 2013
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I tried to rebuild my first carb back in 1980 as a young 19 y/o mechanic in the service. I was trained as an aircraft structural mechanic, so I knew nothing about carbs. It was a 2 bbl from a 225 slant six Chrysler aircraft tow mule and I forgot where a bunch of the parts went lol. I was disappointed with myself and told my supervisor with my "tail between my legs". He said don't worry, just take the little parts, either dump them inside the carb or throw them away and go to the parts store and exchange for a rebuilt one. Since then I've got more proficient with carbs and don't think they're any problem now.
 
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Apr 15, 2010
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I'm younger also, born in 1990. I've grown up around small engines, antique tractors, older cars, etc. I appreciate the simplicity of carburetors and they can be fun to tinker with, but to rely on daily? No way. Ethanol fuels and carburetors do not mix, regardless of what piece of machinery the carburetor is on. If any carbureted engine sits around for any length of time with ethanol fuel in it, you can almost bet money that it will be a bear to get going again. Not to mention the quality of rebuild parts is not great these days. I work in IT, so I fully understand the struggle with electronics too, but I think ethanol fuels were the last nail in the coffin for carburetors. All the fuel in my state pretty much is 10% ethanol, and no, I'm not driving to the airport to try and sneak some AVgas to run in my lawn mower.
 
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There are simple carbs like AFBs and Holley 750 vacuum secondary carbs. There are complex carbs like QuadraJets.
The simple carbs are fuel dumpers and work well at WOT; oftentimes outperforming fuel injection.
The Q-Jet is the best running carb unless it has been commercially rebuilt. Then they are likely garbage.
If they are in good shape and sized properly, just adjust the idle mixture screws for highest manifold vacuum and you should be good to go.

The best Q-Jet rebuilders are a dying breed, unfortunately.
 
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Oct 23, 2017
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VA
I've got a ton of stuff that still has a carb on it, oldest being a 1949 Farmall C with a cast iron carb on it. Have Keihn FCRs on quads, Mikuni carbs on quads, Holley carbs on boats, bunch of china jobs on the Stihl equipment etc. Generators all have carbs. Carbs don't bother me, I use non ethanol in the yard maintenance stuff. The stuff that gets E10 I install in-line fuel shutoffs on the things that didn't already come with one, then just run the carb dry when I'm done with it.
 
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There are simple carbs like AFBs and Holley 750 vacuum secondary carbs. There are complex carbs like QuadraJets.
The simple carbs are fuel dumpers and work well at WOT; oftentimes outperforming fuel injection.
The Q-Jet is the best running carb unless it has been commercially rebuilt. Then they are likely garbage.
If they are in good shape and sized properly, just adjust the idle mixture screws for highest manifold vacuum and you should be good to go.

The best Q-Jet rebuilders are a dying breed, unfortunately.

If you have the time and the parts you can dial in a Q-Jet to a very precise degree- primary metering rod/jets, power piston spring, secondary meterin rods, metering rod hangers, and secondary air valve tension can all be tuned to suit a particular engine. I spent a lot of time rebuilding them for myself and for my friends during my misspent street racing youth.
 
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Jul 14, 2020
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Carburetors can be relatively clean IF they are always operated under pretty much the same conditions. Of course, that's not the case for most things, especially street cars.

By the mid-1980s, the hold-outs on carbs were using technology like feedback carbs, which usually use an O2 sensor and use the data from that to adjust the mixture on the fly. It was a band-aid when close-loop FI was a better solution, but at least up to a point it was apparently less expensive and easier to implement than going to EFI.

Even by the late 70s, carbs had gone from the friendly "adjust them on the side of the road" devices to basically not making any end-user adjustment(idle or mixture) not easily accessible.
I remember my first emissions test ever with my 87 Cutlass, factory 305 Chevy with non ECM carb/distributor. I just had new dual exhaust installed with brand new cats. The HC were 9 (limit was like 100+), co was 0.01 (a small fraction of the limit) and NOx were like 100 with a limit of 900 or something like that. I was so excited when I saw how well it did. The quadrajet had been recently rebuilt and was original to the car. 120k miles on it at the time.

NOx always seemed to be the tough one to pass on these cars, especially if EGR wasn't working or timing was over advanced.
 
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NOx always seemed to be the tough one to pass on these cars, especially if EGR wasn't working or timing was over advanced.

If you look at the chemistry of how the various pollutants are formed, you can see why it's easy to hit either CO or NOx, but how they can kind of fight each other.

CO(and VOCs, although I'm not sure if any sniffers look for those) primarily come from incomplete combustion. Probably your two biggest causes of that(at least in a nice, tight engine) are rich mixtures and retarded timing.

Advancing the timing and leaning out the mixture should nearly kill CO, but that also increases cylinder/combustion temperatures. High temperatures and lean conditions promote NOx formation. That's a lot of the idea behind EGR, at least as I understand it-bleeding relatively cool exhaust gas into the intake should help keep temperatures down. If I'm not mistaken, since higher compression ratios tend to lead to higher temperatures, this is also why C/Rs for the most part took a nosedive in the 1970s. The fact that we can now have cars with high C/Rs on 87 octane and making huge amounts of power with smaller and smaller displacements while also being cleaner than ever is truly astounding.

I hate to keep talking about MGs, but they're what I know best. Starting in 76 or 77(don't remember off the top of my head, and too lazy to look it up now), MG ditched points in favor of an optical trigger, which should in theory give more consistent ignition. As a side note, the first Lucas-designed electronic ignition had horrible reliability. In '79 or so, they started using the improved Lucas CEI, a really good system and also nice that you can buy an inexpensive replacement board at pretty much any parts store in the US as it's the same as GM's HEI. They used traditional mechanical and vacuum advance up to the end. The mechanical advance curves are really steep. In addition to that, a while earlier they had switched to manifold advance(these little engines like ported advance a lot better) and the vac can was fairly aggressive. The late cars are 35º max mechanical, and 24º vacuum that starts at 3"Hg and finishes at 11"Hg. For reference, I run 32º max mechanical and have a 5-15-10 vac can(starts at 5", ends at 15", adds 10º).

With all of that said, when I was growing up, my dad had a 1980 Porsche 924 with K-Jetronic. It had no end of problems with fuel injection seemingly between dead pumps and clogged injectors, although admittedly a lot of that was probably from lack of driving. My sister's first car was a mid 80s Volvo 240, which I think had some variant of Jetronic. Hers was a lot more dependable, but it seemed to be difficult to find somewhat who knew what they were doing to fix it correctly. I've heard horror stories from other people dealing with various Jetronic systems, mostly ones that have been neglected, and having seemingly no end of problems, and of course properly diagnosing problems requires a whole different set of tools(and the know-how to use them) than any carb. No doubt K-Jetronic and later systems are excellent when working properly, but from what I've seen it's a system that definitely likes to be used/driven and not sit. Of course, carbs can varnish up badly and have other issues when they sit, but there's a certain aspect to being able to actually see it operate with your eyes rather than having to just trust your test equipment as you have to do with a lot of FI.
 
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By the mid-1980s, the hold-outs on carbs were using technology like feedback carbs, which usually use an O2 sensor and use the data from that to adjust the mixture on the fly. It was a band-aid when close-loop FI was a better solution, but at least up to a point it was apparently less expensive and easier to implement than going to EFI.

I mentioned before the SU on the Montego with the stepper motor on the main jet. Seems such a logical step, but with no emulsion tube the droplets coming out of the main jet are just too big for efficient combustion.
 
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Aug 8, 2008
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There are simple carbs like AFBs and Holley 750 vacuum secondary carbs. There are complex carbs like QuadraJets.
The simple carbs are fuel dumpers and work well at WOT; oftentimes outperforming fuel injection.
The Q-Jet is the best running carb unless it has been commercially rebuilt. Then they are likely garbage.
If they are in good shape and sized properly, just adjust the idle mixture screws for highest manifold vacuum and you should be good to go.

The best Q-Jet rebuilders are a dying breed, unfortunately.
Sean Murphy is the man for Qjets, started out with Jet Performance then broke out on his own, have a couple of E4ME Qjets for my truck that will be sent to Sean when the time comes for a rebuild.
44-5395-WM4-1.jpg
 
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Somebody jogged my memory. My timing light failed back in my VW Bug days. I tuned the Jeep 360s by ear and a vacuum gauge. Timing marks were impossible to see anyway. :cool:
 
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Decatur AL USA
If I had a dollar for every needle and jet I've changed and air bleed or fuel bleed I've adjusted I would be a rich man. Used to have to re-jet the old 2 strokes every time you got a little different race gas or the temp changed to keep them sharp but so it wouldn't seize on a long pull up top.
 
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Sean Murphy is the man for Qjets, started out with Jet Performance then broke out on his own, have a couple of E4ME Qjets for my truck that will be sent to Sean when the time comes for a rebuild.
View attachment 26506
I've had zero experience with the electronic q jets because Canadian spec cars got away with old fashioned basic q jets and no ECM right throw 1987. I always heard of way more trouble with the electronic ones.
 
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Jul 14, 2020
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Somebody jogged my memory. My timing light failed back in my VW Bug days. I tuned the Jeep 360s by ear and a vacuum gauge. Timing marks were impossible to see anyway. :cool:
Timing marks are almost impossible to see on my 350 olds also.
 
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