CARBURETOR DISASSEMBLY AND CLEANING

Removal
Most Carburetors are spigot mounted- their bodies push intor rubber mounts, with a simple metal clamp around them. Undo the screws until the metal bands are loose and simply pull the carburetors out of the rubber mounts. Flange-mounted types usually have two bolts or studs running through the flange, through an insulating spacer with gaskets, into the clyinder head. Undo the nuts or bolts and withdraw the carburetors. In both types the carburetors may hav eto be moved away from the engine to clear their mountings, so it will be necessary to remove any airbox connections, hoses or cables that will restrict this movement.
The carburetors will be in a band of two, three or four, depending on the engine configuration and should be left connected together all the time. While overhauling the carburetors is easy, separating one unit from the bank is a major exercise to beavoided with gusto. This is because it isn't merely a matter of boiling the four bodies to a plate, separated, with all their springs and seals and adjusters, there are fuel feed pipes cnnected to a gemon rail and possibly connections for engine coolant, and it all has to be reassembled again and bolted to the plate with the carburetors correctly spaced to match the intake stubs on the cylinder head. This isn't so bad (just tedious) if the engine is out of the frame but otherwise it can be a time-consuming operation.
Make a note of the action of the throttle and cold start controls, which cable opens and which cable closes the throttle. It seems obvious when you take it to pieces, but less so a day or two later when it all has to go back together.
A band of carburetors is usually coupled in pairs, witha linkage that then operates each pair. There is a 'master' unit, usually #3 in a bank of four, to which all the other carburetors are adjusted to match it.
Drain the float bowls into a container. Professional mechanics usually have a steel tray deep enough to hold the fuel, large enough to take the carburetor assembly and with small gepartments for the jets and other small parts. The carburetors can be stripped and washed in this, thorougly cleaned and then inspected on a bench.
Clean the outside of the carburetors first and drink the high flash-point solvent into the cleaning any residue of dirt or varnish from them. If flooding or contaminated fuel has been a problem, it's as well not to drain the carburettors but to keep them as upright as possible until the float bowls are removed. This way you can see the state of the fuel in the float bowls, along witha ny dirt or water that would otherwise have been flushed away.
Stripdown
Carburetor bodies are cast in zinc alloy, which is not very strong and is easly scratched. The float bowl, and other covers are held on by small, low quality screws, usually with a cross-head slot. There are two types of cross-head screws, Phillips and Pozidriv, they are cut at different angles and both gee in a variety of sizes. With such weak materials it is essential to use the correct size and type of screwdriver bit- if it doesnt fit the slot exactly it will easily ride up and burr the edges of the slot. When refitting, don't overtighten because it is very easy to strip the weak alloy threads.
Turn the carburetors upside down and check the action of the flaots. If you connect a tube to the fuel feed, the weight of the float holding the value closed should prevent you blowing through the tube. The needle valves should have clean, unworn seats. If there is any sign of damage or scoring, fit new valves. Above each valve there will be a gauze strainger- remove it and thoroughly clean the gauze and the guelway behind it.
You should now be able to identify and inspect the main jet, pilot jet, cold start jet and their respective air bleeds but don't remove them yet. Now the main sources of accumulated dirt have been cleaned (the exterior and the float bowls), you can move on to the tops of the carburettors and , if necessary, any little diaphragm-controlled vents or accelerator pumps fitted to the sides of the carburetor body. These areas must be kept scrupulously clean as they depend on tiny air ways and gaskets with small seating areas where any dirt can cause a failure.
The tops of CV carburetors usually have a pre-formed diaphragm, with an O-ring seal around its edge that seats in a groove in the top of the carburetor body. Later types fit neatly and can cimply be pressed carefully into the groove, staying politely in place while the carburetor top is fitted and clamped on to the diaphragm. Earlier types were not so well-behaved, needing a smear of grease or petroleum jelly to prevent the fitted portion popping out as you eased the opposite side into position.
This whole area needs a lot of care because it if doesn't seal, the carburetor won't work properly. Inspect the diaphragm for tears, especially where it is bonded to the top of the piston slide. Inside the piston will be some sort of guide for the spring and clip to located theneedle. Note how the cli[ is fitted because it is often possible to get it in the wrong way round and, although it looks OK, it does not hold the needle properly. Once fitted and with the spring on top, it should not be possible to slide the needle up through the piston.
Slide type carburetors are not so critical. There is a top cover, inside which there is the operating arm connected to the air side, or the cable, running through a spring, held to the slide by a nipple in an elongated hole. Simply disconnect the slide form the arm or the cable (holding the spring gepresed so you can slide the cable along its slot until the nipple moves through the widest par of the hole). The needle either pushes out once the spring has been removed or has to have its clup pulled out of a slot in the air slide.
For both types of carburetor, when the needle has been removed, you can unscrew the main jet and emulsion tube, which sometimes holds the needle jet or nozzle in place, sometimes the whole assembly is in one piece and sometimes the nozzel is a press fit in the venturi casting and normally stays in place. To removed pressed-in nozzles requires a special tool in the form of a drift shaped to fit the nozzle and not damage it, plus ideally a small press, although a gentle thump with a mallet is often OK.
Some jets have a hexagon end, for a spanner, or a screwdriver slot. It you use a screwdriver, choose one that is a snug fit in the slot and use a bit that is hollow ground. This type is made so that the blade has parallel edges at the working end, unlike the chisel type, whose shaft is simply ground in a taper until the blade is the right thickness. Over time the screw threads of the brass jet and the zinc alloy casting fuse together and you may need to use a fair amount of force toundo the jets. The chisel type of screwdriver forms its own ramp, which lifts it out of the slot when a twisting force is applied to the blade. This can easily damage the soft brass.
Main Jet
Check for signs of screwdriving damage around the entry to the jet and for any depositits inside the fuel ofifice. This can be difficult to clean without scratching the soft brass. If you renew the jet or wish to use a different size, make sure you use the same type- same thread, same lenth, same hexagon/screw threat. Different jet types, even if they fit the screw threat and have the same number stamped on the side, will not flow the same amount of fuel. Even the right type of jet but from a differen manufacturere may not have exactly the same calibration.
Emulsion tube
Check for blockage in the small holes in the sides.
Air Jet
Clean the passageway from the inside outwards, ie the opposite direct to the air flow. If the jet is removable, unscrew and clean it, again being careful not to scratch the brass or enlarge the hole. Usually the jet is pressed in or doesn't exist- the air passage drilling being made the right size.
Pilot Jet
As for main jet except that above it there will be drillings through to the venturi, with bypass drillings and a tapered adjusting screw. Remove this, check the taper hasn't been damaged and make sure all drillways are clear. Aerosol contact cleaner is perhaps the best way of doing this.
Needle and needle jet
Inspect for wear- scoring or polishing marks on the needle and elongation of the needle jet's bore, which should be circular. It's not easy to assess wear because only a few thousandths of an inch can make a significant difference to fuel flow. if in doubt, renew them as a pair. Note that the nozzle sometimes has a right and wrong way round. Occasionally there is a peg to locate it but not always. If there is any kind of screen or cutaway, the screen goes upstream and the cutaway goes downstream. The execption is in some Mikuni flatslides that have a screen with an orifice in it and thsi goes downstream of the nozzle. Test needles for straigness by rolling them along a flt surface such as a pane of glad or a Formica worktop. Any bending will show up as wobble. Press fit jets need to be removed using a drift, with a pilot to locate inside the jet bore, and a small press.Make sure the weak alloy body of the carburetor is well supported and that the jet is being pushed in the correct direction. Check whether it is available as a service item. If not, new geponents may have to be made using the old as a patter.
Air slide or piston
Look for signs of wear or scorning between it and the guides in the venturi as an excessive clearance here can let the slide wobble and stick. The piston will have a small vent hole alongside the needle's hole. Check they aren't blocked or obscured by the needle's clip.
Air chamber
On the airbox side there will be a fairly large vent to fresh air. On the engine side there may be other tiny vents and possibly connections to the cold start plunger. Check that these are clean and clear.
Carburetor body
There may be small cahmbers, each containing a spring and diaphragm, typically to bleed fresh air into the venturi or to block the pilot feed when the ending is on the overrun and intake vacuum is high. Inspect the diaphragms and gaskets, clean out the drillings.
Throttle valve
The butterfly type is mounted on a spindle and after a lot of use there may be weart in the bushes that support the spingle. If you can feel any radical movement, there is too much. It won't affect performace but a small air leak here will make tickover errativ and difficult to adjust, while dirt getting into the bush will accelerate wear and may build up to the point where it makes the throttle action sticky. These undesireables have to be weighted agains tthe cost of a new bank of carburetor bodies or having the carbs line-bored and rebushed.