carb 101

[dub88acc]

] :nuts: :nuts: :nuts: i am relatively new to the carb scene and i don't understand jack. please don't flame me in telling me to search!! Because i already did, and all i find is how to tune up a carb, yet i don't get it. all i want is a carb website or someome to explain to me what every part on a carb does and how it works. plz don't send me to howstuffworks.com either i tried that. i know i need a book on a how acarb works for dummies. anyways, someone plz help me.[/FONT]

[k-roy]

Don't feel bad, I know shit about the keihn (what we have). Most of what know is about Hollys (muscle cars)

You can get the factory manual about your 3G from www.pauldesign.ru
It is the best info you can get about the carb.

[shepherd79]

every carb works the same way.
if you finished reading how the carb works on the howstuffworks.com and you still don't understand, i am sorry but nothing will help you to understand.

[dub88acc]

any other recommendations. i'm planning to put aweber on my lx, just want to know everything about a carb.

[k-roy]

You can get books specialized about webers.

[POS carb]

yea man I was looking also, how stuff works only goes into talking about the basic function and they show a stupid lawn mover carb, which is a differnt style.

The BASIC carb (not the vacuum-choked keihin) uses engine vacuum to suck in air and gasoline.

Basic types:
2 barrel, 4 barrel - number of intake ports
Mechanical/vacuum secondary - this designates how the extra barrels open. On a mechanical they are opened by pushing the pedal, on a vacuum they open up using engine vacuum.
Synchronous/progressive - How the barrels open, synchronous means they open all at the same rate, progressive means one opens, then the other.


carb body:
The carb has 3 main parts, the top hat (covers everything, holds choke and the air cleaner) the body (the bowl for the fuel, the jets, power valve, venturri and boosters) and the throttle plate on the bottom (regulates the flow with butterflies)

Basic parts:
It regulates the air coming in with the throttle butterflies (the circles that open and close inside when you push the pedal). When you push the pedal it pulls the cable and this pulls on the butterflies.

It regulates the mixture by using "jets", jets are just round pieces of brass with holes in the middle, they are at the bottom of the fuel bowl, and depending on how wide the hole is regulates how much gas is mixed with the incoming air. Bigger jets flow more gas so the engine runs richer and vise-versa. The air being pulled into the motor causes a vacuum effect and this pulls the gas through the jets. A car needs about 13 parts air to 1 part gas to run well.

Accelerator pump is another part, this shoots gas into the carb kind of like a water pistol works. When you press the pedal suddenly, the carb can't deliver the proper ammount of fuel instantly, there would be a delay or an engine stall. This pump shoots gas when you push down on the pedal and smooths it out until the vacuum takes over.

additional parts for better drivability:
Now comes the venturri, this is the narrow part of the carb barrels with the metal piece that goes in the middle of each (venturri boosters). Basically the narrowing causes an increased suction for better fuel mixture
the boosters just let the gas be injected at the center of this venturri.

The power valve is a valve at the bottom of the bowl that is regulated by engine vacuum. While the car is idling there is lots of vacuum in the intake, around 20in-Hg, and the car is using very little fuel. When you punch it the vacuum drops to 0, and this drop opens up the power valve to allow more fuel into the jets.

choke:
gas does not burn in liquid form, only the vapor burns. If you spill gas on the floor and light it, only the evaporating fuel is on fire. when your engine is cold the gas is not vaporizing so you need to add more gas until the carb is warm enough, this is where the choke comes in. The choke goes over the venturri/jets so that when it's closed and you press the gas the airflow is restricted but the increased vacuum draws more fuel through the jets/boosters. The choke can be manual (a pull-cable type), electric (the cars electricity heats a coil attached to is that expands and causes it to rotate open), or water (same as electric only it uses the engine coolant to expand the coil)

the Honda stock carb has a multitude of extra vacuum taps in it to run emmissions control devices. If you hook up a REAL carb to it you will have 2, maybe 3 at the most. 1 runs the EGR valve, another can be for the distributor (or you just hook it direct to the manifold), and the other could be for vacuum secondary

ok that should sum it up pretty good. It's obviously a slow day here at the office.

[x3r0]

Very good basics :-) thanx man.

[OptimusPrimeSr]

choke:
gas does not burn in liquid form, only the vapor burns. If you spill gas on the floor and light it, only the evaporating fuel is on fire. when your engine is cold the gas is not vaporizing so you need to add more gas until the carb is warm enough, this is where the choke comes in. The choke goes over the venturri/jets so that when it's closed and you press the gas the airflow is restricted but the increased vacuum draws more fuel through the jets/boosters. The choke can be manual (a pull-cable type), electric (the cars electricity heats a coil attached to is that expands and causes it to rotate open), or water (same as electric only it uses the engine coolant to expand the coil)


(sorry to bump such an old thread, but I'm in the middle of troubleshooting an issue and have shit for knowledge wrt carbs)

The quoted paragraph (especially the part in bold) caught my eye. Recently, my car has started to idle erratically while warming up and I can hear it struggling. If I'm not careful with the gas pedal, it will die as I start to pull out from park. Once the engine is 1/2 way to the warm mark on the temp gauge, all is well and it runs like the dream I remember.


Based on the quoted and bold, i believe it may be possible that my engine isn't getting enough gas when its cold. I just had a bad fuel pump replaced (along with the rear fuel filter) in Dec2009...the one they replaced it with died within 5 months so they replaced it again for free in May2010.

I need a little direction from you experts. I love my car and believe it has at least another 75-100k mi to offer me.

anyways, based on the quoted and bold, i believe it may be possible that my engine isn't getting enough gas when its cold.


btw, 87 LX 4dr




UPDATE: decided to check the timing and pulled off the dizzy cap and found a small puddle of oil along with 4 worn out leads and rotor. the cause...looks like the bottom bolt was loose and the bottom of the dizzy and top of tranny housing was coated in crud. I cleaned it all up, tightened the dizzy, replaced both the dizzy cap and rotor, and she seems to be a little better...so far.

[bryan42688]

take it apart and figure it out , there is a venturi choke float coolant air jet controls i would recommond going to a junk yard pulling a stock carb take it home and fiddle with that ,


for people who cant leave by reading or watching they should try experiencing before giving up

[2oodoor]

I can only add to this that if you go with a junkyard carb make sure it hasn't set for too long because old evaporated gas can be hard to clean out. sometimes it turns hard and whitish looking once its past the varnish stage.