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Weber carby anatomy, rebuild and tuning
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Author:  bumstein [ Fri Jul 15, 2016 7:32 pm ]
Post subject:  Weber carby anatomy, rebuild and tuning
Hi folks. Decided to strip my Weber copy carby down, thought I'd bung a few pics of the process here in case anyone is interested.

Although it's a FAJS, anatomy should be roughly similar to a Weber.

Working on a clean bench with paper and a bluey down (ask any nurse or associated profession to nab you a bluey, they're great for this kind of work).

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Remove the circlip that holds the choke butterfly activation arm on. I've already lost mine, so saves me time. They are easy to lose!

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Remove the six screws holding the top section on and off it comes

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On the side of the throttle body is the carby ID info. In this case it just tells me it's a FAJS Carby. Cheap copy of a real Weber. This info might help in getting hold of a rebuild kit.

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Flipping the top section over, pull the pin that secures the float. Remove the float and the needle valve will come with it.

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Save gasket or peel and clean up the surface of your replacing it.

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The power valve diaphragm may require replacement. To test it press the spring down shown in pic 1. Cover the hole shown in pic 2 and release the spring, the vacuum should hold the spring down.

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Three screws to remove the power valve

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10mm socket and remove the needle valve seat, don't forget the washer.

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19mm socket or ring spanner to remove the brass nut, inside is a wee basket fuel filter.

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Four small screws and you can slide the choke butterflies out, then remove the shaft. Be careful on the small screws, they can be difficult to remove and easy to round off.

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14mm socket or ring spanner will remove the other two brass nuts, 11mm fit my fuel inlet fitting.

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This destructs the top section. Get in and clean it with carby cleaner and a green scourer.

I usually put this section back together before destructing the bottom section so I don't have too much stuff loose at any one stage.

I will post pics of the lower half next week when I get to it.
Author:  HarryHoudini [ Fri Jul 15, 2016 8:52 pm ]
Post subject:  Re: Weber carby anatomy
Thanks for making the effort,great stuff.
Author:  bumstein [ Fri Jul 15, 2016 9:35 pm ]
Post subject:  Re: Weber carby anatomy
No worries!! It's not a comprehensive A-Z of the carby but it might come in handy for someone.

I have had the intention to do the same for the stock carby, even have most of the pics but haven't had the time to compile them. This way if I do it as I go it's easier for me :)
Author:  bumstein [ Sat Jul 16, 2016 1:59 pm ]
Post subject:  Weber carby anatomy, rebuild and tuning
Next episode, starting the lower half.

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Remove the air corrector jets at the top of the carb throttle body. Left one is the primary, right is the secondary.

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You can then (probably) remove the emulsification tubes. A small screw driver or Allen key can fit in the tube to gently wiggle it out (gravity assisted). They may be more difficult than this method allows, if be keen to hear others methods of getting it out. To get the tube out my secondary side I had to wait until I'd removed the venturis and pop it out with a fine tipped pick.

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Primary and secondary main jets can be removed with a flathead screwdriver. Primary and secondary are the same orientation as the air corrector jets.

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Remove the primary idle jet and O ring from adjacent to the accelerator pump. There's also one on the secondary side, opposite the primary.

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Remove accelerator pump jet and pump delivery valve assy, note the placement of washers

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The fuel deliver venturis slide out upward. Take note of which side the fuel entry hole is as if they are put back the wrong way fuel won't be able to enter the venturis and no fuel will be delivered into the barrels.

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http://s688.photobucket.com/user/jflock ... 0.jpg.html

Remove the full power needle assy at the bottom of the float chamber.

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Undo the four screws holding the accelerator pump assy together, remove the cap, diaphragm and Spring. As you can see mine wasn't the cleanest assy, perhaps the source of the problems I'm having with this carb at the moment!! Gunge has found its way in and festered in there

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Author:  bumstein [ Sat Jul 16, 2016 2:01 pm ]
Post subject:  Re: Weber carby anatomy
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More to come.. Choke assy next.
Author:  bumstein [ Sat Jul 16, 2016 3:54 pm ]
Post subject:  Weber carby anatomy
Choke assy.

There are a few different types available, water activated (or deactivated really), electric or manual.

The basis of the water and electric chokes is that the choke is activated in its resting state. When the spring warms up (by coolant heating in a water unit or 12v current in the electric unit) the spring inside rotates and turns the choke off.

Remove the three securing screws and remove the choke cap, underneath is the spring that heats up and turns the choke off.

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This is the lever that activates the choke butterfly actuator arm

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Now remove the three long choke assy securing screws

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The choke assy comes free, line the key up with the hole on the lever as pictured here to remove it completely

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Three screws on the choke diaphragm cover come off to reveal the choke diaphragm and spring.

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The choke diaphragm and shaft are now free to slide out.

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Linkages pictured. I don't see a need to remove these on this occasion.

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Author:  bumstein [ Sat Jul 16, 2016 5:01 pm ]
Post subject:  Weber carby anatomy
Throttle linkages and butterflies :) getting down the the nitty gritty now!

Pic as is

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On the primary throttle shaft there's a wee lock tab. Hard to see in the pic but unfold it then get a spanner onto the retaining but. Remove the throttle cable linkage.

(Other carbs might be a little different here, this ones been knocked together and modified in a fairly unsatisfactory manner IMO)

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Sorry about the soft focus.. Carby cleaner on the lens

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Primary to secondary link

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Choke throttle rod/linkage doodad

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Secondary shaft linkage

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Now you can remove the four screws on the throttle butterflies. These may be a bastard to budge!! Be careful not to round them out but expect to use some force. Better this than them falling out into your motor!!

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Turn the shaft and slide the butterflies out. You can then slip the shafts from their spot. Take note where the springs and bushes sit. There's one nylon bush on either end of the shafts.

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Idle mixture screw. If your putting a kit through you might have a new one of these in the kit.

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Choke O ring. Remember to replace this.

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Author:  bumstein [ Sat Jul 16, 2016 5:04 pm ]
Post subject:  Re: Weber carby anatomy
Your now ready to clean a whole bunch of parts!!! I will also remove the Pump Discharge Blanking Needle as I've got crap residing in that wee tube. Photo of that when I get home and have the correct size screwdriver.
Author:  bumstein [ Sat Jul 16, 2016 7:55 pm ]
Post subject:  Re: Weber carby anatomy
Pump Discharge Blanking Needle as promised

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Author:  cairns27 [ Sat Jul 16, 2016 8:27 pm ]
Post subject:  Re: Weber carby anatomy
Like.


bye
Author:  bumstein [ Sat Jul 16, 2016 8:50 pm ]
Post subject:  Re: Weber carby anatomy
Thank you


Bye
Author:  bumstein [ Sun Jul 17, 2016 2:13 pm ]
Post subject:  Weber carby anatomy
Ok... Putting it back together is just a. Reverse process, so start scrolling up!!

There are a few bits that I will
Mention but I will spare you the bother of posting pics of the whole process.

Replacing the throttle plates you'll notice that the edge has a taper on it, difficult to see on the photo but make sure you get that taper in the correct way so when the plate shuts it sits against the carby throat wall flush. The line in yellow is to illustrate the shape.

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Insert the plate and close the throttle, now adjust the plate so it has a perfect fit while closed then put the screws in and secure. This ensures a good fit when closed.

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Order of the linkages in case it's not already clear. I hate mucking these up and having no to work out how they go.

Spring
Choke link and rod
Spacer - make sure you get it the right way round so it fits into the Primary to Secondary Link
Primary to Secondary link
Washer
Spring
Accelerator cable contraption
Lock tab then nut. Don't forget to bend the lock tab over the nut again.

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This is how the primary to secondary link sits over the spacer.

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Reinstalling the Idle Adjusting Screw I placed it the same amount of turns as when I removed it. This should get me a ballpark adjustment and I can fine tune it after.

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Line the choke pin up with the spot on the choke spring and replace the cap. Once the choke cap is back on, leave the three securing screws on loose so you can rotate the cap. Once the choke is all back in place rotate it clockwise until the choke plates are fully open at rest.

This means the choke is fully deactivated, once the carby is back on and the motor cold you can reset the choke. More on this later.

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Reapplying the accelerator pump assy is a little tricky to get it all on, Spring in place without the bits shifting.

I find a shaft that fits the screw holes, place one or two in as pictured, then press the assy down onto the spring. Just helps it stay in place while you get the first two screws started.

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Author:  bumstein [ Mon Jul 18, 2016 11:38 am ]
Post subject:  Weber carby anatomy
Ok, setting up the Weber.

When you instal it on the manifold the only major thing to remember is not to over tighten the securing nuts. Cranked on nuts can pull the throttle body base out of shape and cause all sorts of issues.

To set the idle you need to have the car at operating temperature and idling high enough so the motor doesn't stall. If it is idling too low and stalls, increase the idle speed by the adjustment screw shown in the second picture below.

With the motor running, back the idle mixture screw off until it begins to run rough. Now tighten it until the motor is running at its fastest revs, keep advancing until the revs drop again. Where it's running at its quickest is its premium spot.

Idle mixture screw

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Once the mixture is set, you can set the idle. Tighten the idle adjustment screw to increase, or loosen to decrease, revs. Simple.

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Once the idle is set I like to go back and recheck the idle mixture, fine tune it.

On to the choke

Make sure the car is cold when you set the choke. First thing on the coldest morning your location has is ideal.

The choke works by closing the choke plates on top of the carby and increasing the idle. Idle increase is achieved by a cam lobe holding the choke linkages at three varying stages.

Pictured below;

First stage is when you first start the motor, the choke is fully activated and the revs are high.

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After the motor has started a tap on the throttle allows the cam to move to its second position. This position has some choke and higher than normal revs just to allow the motor to warm up.

Notice the cam is rotating clockwise (if viewed from choke side) to deactivate the choke in its stages. As per silly red arrow :D

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Final position has released the choke and allows the primary linkages to return to their usual warm idle position.

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Firstly when the motors cold I leave the choke power supply off, this only applies to the electric choke although perhaps you can do the same with water choke.

The reason I do this is to set the choke roughly. With the choke fully activated and the motor running, turn the choke cap counterclockwise until you reach the desired amount of starting choke.

Different places with different weather and different cars will require their own amount of choke in order to start efficiently. My car needs about 2/3rds to start in winter here, less in summer. Another car may only require less, so time to feel what the car is telling you.

12v supply off.

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Once this is done I move the choke manually to its warmup position. To move the choke manually, activate the primary throttle linkage and move the choke plates by hand. Watch the cam to make sure it's in the right spot.

The reason you need to open the primary linkage to move the choke is it allows the choke mechanism to unlock and move, without a flick of the throttle the choke won't move. This is also the reason you need to tap the throttle before you start the car, it allows the choke to activate and pops a squirt of fuel into the motor

With the cam in its warmup position adjust the choke revs, this is the amount of revs it runs on when warming up. Again, by feel is the way here.

A flat head screwdriver on the screw that sits behind the choke. Tighten to increase and loosen to decrease choke revs.

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Lastly, I tend to go over all the tuning adjustments again from the start to make sure I have them all correct.

Runs sweet as a nut!!
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