The illustrated carburator guide

[andyb]

First off, a disclaimer or two:

This is meant to be read hand-in-hand with SOG's carb cleaning guide.

The carbs pictured were taken off a heavily dragraced FJ that has not run in a few years.  Worse, they were not drained properly.  They're filthy, inside and out, but the critical passageways are absolutely clean to where you could eat off of them (if you don't mind the taste of leaded fuel).

In short, this is closer to the "before" picture than the "after" picture that you should have when working on your own FJ.  So please, don't blow me a bunch of shit about how filthy things are.  

[andyb]

This is a rack of FJ carbs, the engine side is facing you.  There's UNI pods on the backside, and you can see the throttle blades sitting closed at this angle.

A - This is the idle adjustment screw.
B - The long rod is connected to the choke actuators on each carb by a screw that fits into a divot.
C - There's three of these screws between the carbs, surrounded by linkages with springs in them.  They are for adjusting the synch.
D - There are four of these caps, only one is marked.  They're retained by four screws each, and cover the diaphram/slide assembly.
E - This is where the throttle cables connect to the carbs, they're adjustable for free play at this point. 

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This is the carbs as seen from the back, mostly all you can see is the filters and the diaphram/slide covers.  The pair of screws visible above the worm-clamps on each carb holds them together.

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The carbs as seen from below. 

A - These are the drain screws.  There is one on each float bowl, and they're used for emptying the carbs of fuel, which will pour out of B all over the motor, so connect a line before you loosen them.  Odds are they are frozen in place though, and are easily stripped out.  Easier to run the bike empty of fuel by shutting the gas off and letting it idle until it dies.
B - As stated above, this is the drain for each carb bowl.
C - The adjustment screw for changing your idle rpm.

[andyb]

This is the carbs as seen from above, or what you'd see after pulling the tank.  Is the OEM airbox also in the way?  They connect to the intake rubbers at the bottom (as viewed in this picture).

A - This is the idle mixture adjustment screw.  Each carb has one.  FactoryPro has a good section on adjusting these.
B - This is the screw that connects the choke actuation rod to each choke plunger.  If these are loose/missing, that carb won't have a working choke.
C - This is the carb balance/synch screw for adjusting #1 and #2.
D - This is the choke actuation rod, as described in B. When you pull the choke knob fully out, it should move about a half inch sideways.

[andyb]

This is a float bowl, with the gasket stuck to it.  Four screws held it on, through the holes in each corner.

A - This is a deep hole machined in, it fits over a protruding tube from the carb body.  The choke picks fuel up from here.
B - The gasket is stuck to it.
C - If you opened the drain screw on the bottom, it would take fuel from here until it's empty.
D - This is old gas, rust, and assorted grunge.  It shouldn't be here.  It's also quite difficult to remove, you'll see that I've only cleaned it partially off.
E - This little hole connects with A, and if it's plugged up with D, will prevent the choke from working properly.
F - This little alcove is where the float posts fit.  Once the bowl is in place, the float retention pin can't work itself out very far because it'll hit the bowl in this area.  If you see a wear mark here, it means that there's been a loose float pin rattling around and hitting here.

[andyb]

This is the carb as seen from the bottom, with the bowl removed.  At this angle, the air filter/airbox would connect to the bottom, and the top would be stuffed into the intake rubbers.

A - This is a float.  It's one big horseshoe shaped piece with plastic on the ends and aluminum in the middle.  At this angle it looks roughly like a U.
B - This is the main jet.  It controls fuel at high rpm/big throttle openings.  It also retains a washer and the needle jet/emulsion tube.
C, leftmost - This is a bowl vent.  It's usually connected to a hose that runs down past the motor and prevents gas from covering the engine if there's problems (stuck needle floats!) 
C, middle - Why are there two C's?  Good question.  The one near the main jet is where the pilot jet lives, quite deeply in there.
D - These are air intakes for the choke circuits.  They also probably have hoses connected to them.
E - It's hard to see, but that's a hollow tube that is sticking towards the camera, you're seeing it nearly end-on.  That's the tube that pokes into the carb bowl and carries fuel up to the choke circuit.
F - This is the center portion of the float assembly, and you can see the little wire clip hanging over it.  Bending this little tang up or down is what adjusts the fuel height/float height.




This is the bottom of the carb with the bowl removed, as seen from a different angle.  The airfilter/airbox would be connected to the side nearest the camera.  All markings are as listed above.

[andyb]

This is the carb with the bowl removed, as seen from the airfilter/airbox side.

A - This is the pilot air jet.  Stock is a 155, and that works for most folks.
B - This is the air passageway that communicates with the diaphram area.  If you put a light vacuum on this (suck on it, but clean it first, ewww) and have things assembled, the slide should move.  If it doesn't, odds are you've got a torn diaphram or the slide is jammed/siezed up.
C - This is the slide.  If you stick your finger under it and shove it up (down and to the right in this picture), it'll move and then return when you take your finger out.
D - This is the needle.  It's adjustable, but you can't see that from here.
E - This is the top portion of the needle jet/emulsion tube.  See how the needle goes into it, the needle is tapered, and as the slide moves up, there is more area for fuel to come up and go into the engine.
F - This is the float needle's seat, as seen from the side, under the middle part of the float.
G - Another view of the main jet.
H - Another view of the float.

[andyb]

This is a pilot jet.

A - This is the orfice that meters fuel.  It's tiny, really, really tiny.
B - This is the jet.  Usually these are 37.5, 40, or 42.5.
C - This is a typical Bic lighter, for size comparison.

[andyb]

This is a pair of pilot jets in my hand.  Notice the lack of hair on the palm.  There's two types of jets.

A - This type has holes on the sides.  These don't have any bearing on the fueling, as they're not the metering orfice, they're huge by comparison.  Grunge can form in these holes, break loose, and ruin your day, so it's something to have clean before you put them in.
B - This type lacks holes on the sides.  This is what was OEM.

I believe the OEM lacks the holes; the holes were in theory to make it less likely to plug and easier to clean.  Seems strange, but they have no bearing to fuel flow.  They can however collect junk that breaks off and plugs the metering orfice, so clean them up good anyhow.

[andyb]

This is the idle mixture screw assembly, removed.  In a stock US carb, this is covered by a pressed in plug.

A - This is the screw itself.
B - This is the spring that puts tension on it.
C - This is where it goes into the carb.
D - This is the choke rod.  Not a bad idea to lubricate it where it goes through the carb bodies.
E - This is the screw and paul that hold the choke rod to the choke plunger.  The screw sits in a divot.

Not shown is the washer and tiny o-ring.  The o-ring provides a seal that prevents fuel from coming up and out past this screw, and the washer prevents the spring from chewing the o-ring apart.  Then the spring sits on the washer, and the screw goes in last (though it's easiest to put it all in at once, it's nearly impossible to take it all out at once).  

[andyb]

This is a view looking into the carb from the motor side.

A - This is where the mixture screw feeds into the airstream going into the engine.  It's not really very visible (I really did try, but a photog I'm not!), but I've screwed the mix screw all the way in, and it's sticking out a bit.
B - Yup, that's the throttle blade, or butterfly valve.  Twist the throttle, and that's what you're moving.
C - There's 3 (right?) tiny holes here, right about where the throttle blade nearly touches.  That's where the pilot jet feeds fuel to.


When you're cleaning a carb, one of the critical areas to get clean is to use forced carb cleaner and/or compressed air into where the pilot jet screws in (see a few pictures higher in this thread).  It should come out the holes shown in C in a good strong stream from each.  If you remove the idle mixture screw and blast down it, it'll mostly come out of hole A.  Covering that hole with your finger and spraying carb cleaner into where the idle mix screw was will clean the passageway that feeds it (otherwise your idle mix screws will have little to no effect as they're not being fed anything to distribute).

[andyb]

This is the bottom of the carb (it's upside down on the bench, and the camera is pointed down), with the bowl removed, the main jet removed, and the washer under the main jet removed.

A - This is the float assembly.
B - This is the emulsion tube/needle jet.  Notice the slot cut into it on the bottom left side.  That is fitting over a pressed-in pin to properly orient the emulsion tube.
C - Another view of the tang on the float assembly.  The wire clip over it is connected underneath to the float needle.

Not labled but visible on the right is the fact that the float pin has been pushed out a bit, perhaps 1/8", towards the top right of this picture (directly to the right of the "c" in the picture). A quick tip for making that easier?  If you get too rough, those float posts will break off entirely too easily.  Make a little spacer block to sit between them and distribute the shock of tapping the pin in or out against both posts.

[andyb]

This is the float assembly, with the float needle stuck to it.

A - This is the float needle's rubber tip.  This is the little bastard that's usually responsible when you find a puddle of gas under your FJ, assuming the float needle seat orings are intact.
B - This is the tang for adjusting fuel level/float height, as seen from the bottom.  The float needle's little wire clip is keeping the needle connected, but if I sneezed while taking this picture, I'd probably still be looking for the needle.

[andyb]

This is the carb body, as seen from below.  The bowl, main jet + washer, float assembly, and float needle have all been removed.  Air filters/airbox would be connected to the bottom part of the carb in this view.

A - This is the emulsion tube/needle jet.  You can barely see that it's threaded, that's where the main jet goes (with a washer between the two).
B - This is the float retaining pin (over to the right, the B is hard to see).
C - This is the needle seat.
D - This is the screw and little clip that retain the needle seat.
E - Overflow tube.
F - Choke air intake tube.