How does the carburettor work?

[beepbeep]

OK, I'm pretty well informed when it comes to how various versions of EFI work, was unfortunately forced to learn how CIS work and have vague insight on how MFI works.

But what about carbs?

I just bought a carbed beater to get me trough the salt-covered winter roads and finally came to conclusion that i don't know very little about carbs.

All other fuel systems have at least two input variables: throttle opening and RPM. The more you open the throttle the more fuel needs to be pumped into the engine to achieve somewhat constant mixture. Also, the more you rev the more fuel is going to be used per time frame.

How about carbs? I understand there is a combined throttle/fueling element there and that thottle opening also adjusts amount of fuel going trough it...is there some sort of CIS-lookalike "flapper" built-in that keeps track on how much air is going trough the carb and adjusts fuel accordingly?

How about fuel-return? I noticed my car has only one mechanically operated fuel pump...is it providing more pressure the more i rev or how does it work? I couldn't find ruel-return line either...must be a mess to adjust those things right.


Sorry, but i kinda never fiddled with this stuff...had computers when i was a kid

[yelcab1]

How about reading a book on the subject. Haynes has excellent books on webers. You are asking some serious questions about an entire fuel delivery system. A quick paragraph will not do it justice.

[beepbeep]

A book? Nahh...i don't need no book :-)

I just did a quick read on the subject @ "Howstuffworks". I understand that there is a venturi in the center so pressure-drop across it sucks out fuel from the fuel jet so the more air goes to more fuel it provides. Obviously, this cludge only works at limited range so there seems to be additional mechanics to make whole caboodle work at operation extremes (like full-throttle, idle and cold-start).

I'm just reading some more here:
http://www.roadkill.com/~davet/moto/carb.monologue.html

[jmz]

...better than your spell check.

Carbs are pretty simple but require some experience to tune right.

I suggest you read a book.

[yelcab1]

At coldstart there is a choke to make it richer, or with weber, a whole new circuit.

At idle, the air/fuel is mixed in the atomizer, goes into a jet, gets sucked into the carb, and you can change the air/fuel mixture by adjusting a screw.

At half throttle, there are progression holes to aid in a smooth fuel delivery curve. The amount of openess of the butterfly changes the amount of suction and more fuel/air from the main jet is sucked into the carb to result in more combustion and more speed

During acceleration, there is a acceleration pump to deliver more fuel at full throttle for immediate acceleration

Really, read a web site or a book for more details.

[beepbeep]

...better than your spell check.

Carbs are pretty simple but require some experience to tune right.

I suggest you read a book.

Well I can it again in prefectly spelled swedish...

No, i was just wondering on how it works...i'm not going to tune it as it seems to work OK for now. I heard horror stories about extensive fuel consumtion but it is relativly frugal.

[beepbeep]

Originally posted by beepbeep
Well I can post it again in perfectly spelled swedish...

No, I was just wondering on how it works...I'm not going to fiddle with it as it seems to work OK for now. I heard horror stories about extensive fuel consumtion but car is relativly frugal.

[Randy Webb]

The big valve that lets air go past is tied to the gas pedal.

That's the simplest possible explanation. You DO need a book to tune them. Do everything else to ignition, valves etc before tuning the carbs.