Author Topic: Hagerty's article on how carburetors work  (Read 163 times)

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Offline elagache

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Hagerty's article on how carburetors work
« on: June 21, 2017, 05:29:59 PM »
Dear mid-60s "fix'em up" types,

Hagerty is continuing to have articles on maintaining various classic car components.  In this newsletter, there is a basic but helpful explanation of how carburetors work:

https://www.hagerty.com/articles-videos/Articles/2017/06/15/understanding-the-carburetor

Unfortunately, the key diagram is somewhat difficult to view because some horrible color choices, but it is a clear and helpful explanation of how carburetors work.  There were a few highlights that I found interesting.  One quip I'm curious about is this one:

Quote
If everything is working the way it should, the ideal ratio of air-to-fuel for efficiency, by weight, is 14.7:1

Having taken the plunge into a laptop adjustable electronic fuel injection system, I'm aware that getting this value as close as possible to the engine's "mellow spot" can make an amazing improvement in the engine's driveability and noise reduction.  So I'm curious: Just how well does a carburetor regulate the fuel-air mixture throughout the power band?  Alas this piece doesn't answer that question. 

This is the other quote that seems like sage advice:

Quote
If you’re more inclined to take your carburetor to a professional for service or repair, that’s certainly an option. But consider this: carburetor technicians are a dying breed. Good ones have become much more difficult to find, and they are likely swamped with work.

I do hope that somehow carburetor specialists don't go completely extinct.  Because if they do, one after the other, carburetor equipped classic cars of all ages will eventually become inoperable. 

Cheers, Edouard 

Offline TrunkMonkey

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Re: Hagerty's article on how carburetors work
« Reply #1 on: June 22, 2017, 11:06:40 AM »
Regarding the ratio and how well a carb maintains the optimum.

If all the circuits are properly working and adjusted, (as well as correct metering etc.) then the ratio will always be correct across the RPM range because it is vacuum based metering (except for the accelerator pump).

Airflow controls fuel "pickup/flow" into the stream, and variances are very minimal. The transitions are the biggest points of variance.

There are a great many factors other than carburation that affect, god or bad, the proper production of power.

EFI does a lot for smoothing out the transitions and adjusting to the variances, faster and often better than the mechanics/physics of carburetors.

 :tongue3:
Michael

The first 60 years were spent on surviving. The second 60 are gonna be spent on fun!

Offline elagache

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Would love to see a "shoot-out" article. (Re: How carburetors work)
« Reply #2 on: June 22, 2017, 04:02:10 PM »
Dear Michael and mid-60s Buick "so how does that really work?" types,

Regarding the ratio and how well a carb maintains the optimum.

. . . .

Okay thanks for your explanation.  I'm not sure I got my head around it, but it will due for now.

Still, I've gotten spoiled by the neat graphs that can be generated by the FAST Sportsman software.  I sure wish some car magazine would setup an engine with EFI and run it through its paces on a dyno.  Then put a carb on the same engine do whatever jury rigging would be needed to allow the EFI instrumentation to pick up the fuel air ratio and whatever other parameters they thought were worth comparing.  It doesn't sound that difficult and the results should be really interesting.

Oh well, perhaps someday . . . . .

Cheers, Edouard  :occasion14:

Offline WkillGS

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Re: Hagerty's article on how carburetors work
« Reply #3 on: June 22, 2017, 10:55:49 PM »
Regarding the ratio and how well a carb maintains the optimum.

If all the circuits are properly working and adjusted, (as well as correct metering etc.) then the ratio will always be correct across the RPM range because it is vacuum based metering (except for the accelerator pump).
......

There are some exceptions... Carburetors don't have the ability to adjust mixture for variations in air density ...altitude or winter vs summer temperatures (except for the choke used for warm-up).

A useful tool for tuning is a wide-band air-fuel ratio gauge. It will tell you whether the mixture is too rich or lean. It will also help to teach you what a too-lean condition (surging) 'feels' like.
For WOT runs, it's a good idea to have a slightly rich mixture in the 12:1 range to prevent detonation and engine damage.

Walt K
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