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1st Gen Carburetor Service

The carburetors on your Venture are not terribly complex and are readily serviceable. There can be a lot of time involved depending upon how much you need to disassemble. The project is not exactly simple, but with some basic mechanical skill and experience, and a little guidance here, you can avoid a hefty shop charge and do it yourself. Set aside plenty of time (most of one day) and use care throughout the process. Don't rush. It takes better than an hour to remove and replace the carbs. The remainder is bench-time. It's worth the effort to be thorough. Lubricate whatever you take apart; jet plungers, o-rings, drain screws and their o-rings, etc. Replace anything that is showing wear.

Refer to the flow diagram at the end of this article to determine the path of air and fuel through the carburetor. You can follow the form of the carb body casting to visualize much of the path. If you are cleaning the carbs, force air and carb cleaner in the opposite direction of flow when possible. A jet table is provide at the end for reference; they're easy to get mixed up.

There are some gotcha's:

Lost, broken or mixed-up parts can be a setback. Springs and retaining clips can fly (as Neil86 says "where'd that spring land??"), in particular the carb synchronization tabs have springs that are retained solely by the brackets that join the front/rear carb pairs together. C-clips on the choke and throttle rods like to fly. Plastic parts can break (new floats are unavailable for the early models.) Be as gentle as you can with stubborn parts.

Drop something into the engine's intake with the carbs off and valves open will make a lot more work for you. (Cylinder head removal, possible bent valve.)

Throttle cable problems - know where your engine kill switch is in case the throttle ever gets stuck open.

Fooling with gasoline has its own inherent risks. No sparks or open flames, please. Turning the ignition on with the carbs out will result in fuel being pumped everywhere, and the ignition can spark if the pickup sensor is in the right position.

If the fuel lines have never been changed, this might be a good time to consider replacing all the hoses and filter. They can be a source of contamination.

Some things in the images here are not quite right and could confuse you: Figure 1 has the YICS hoses routed away for a sync and testing, Figure 3 is missing the wire-loop for the vacuum advance hose in the upper right of the #2 carb, Figure 17 has the fuel-hose support wire-loop attached one screw too far to the left, etc.

Tools:

• phillips screwdriver set, good quality, unworn tips, always use the correct size
• flat blade screwdriver assortment, one in particular with a small but strong tip, I call carburetor sized
• needle-nose pliers
• vise-grips
• smallish radiator hose pick: a dull tipped, tapered, smooth-round hook used to coerce stuck hoses or rubber boots
• small diameter nylon bristles from a scrub brush (optional, to scrub jet barrels)
• carb cleaner (wear safety glasses, avoid getting anything caustic on diaphragms or plastic parts)
• blue Loctite
• compressed air
• a clean bench area to work on the carbs
• carb synchronization tool (carbtune or similar manometer)

Airbox Removal:

• Remove both side panels, lower fairings, triangular trim grills, and the top tank/air filter panel.
• Disconnect the battery.
• Clean the carburetor area and area above the carbs in general. You do not want crud falling into the intake valve chambers.
• Remove the air filter cover and filter.
• Loosen the crankcase ventilation hose where it attaches to the crankcase in the near-center of the engine's V (Figure 1, A). This is best accomplished from the right side. Slide the pinch-clamp up beyond the crankcase vent-pipe contact area. Wiggle it enough so it floats free.
• Loosen the four airbox boot clamps, one per carb. Unscrew the clamp almost all the way (screw not completely out of the clamp) so the clamp is floating freely. Work the base of the boot free from each carb individually. I might use the radiator hose pick to carefully get under any stuck boot edges and slowly work them free (without tearing the boot!)
• Disconnect the drain hose in the bottom left-front corner of the airbox.
• You should now be able to lift the airbox straight up. There should not be any real effort involved if everything is worked free. Do not use force. If something is binding, investigate and free it up.

Figure 1

Carb Removal:

• Drain the carbs. There drain screws are near the base of each carb (Figure 3, A, for example) and they will drain via the hoses sticking out the sides. It's messy, and because of that, I might not even drain them, but keep aware they're full of gas still if you don't.
• Remove the fuel-feed hose (from the fuel pump) in the top-center of the carb bank. It is the only hose with a clamp. Use the radiator pick to free it up (carefully) if it is stuck. Pay attention to how the hose is routed. Gas will spill.
• Remove the four vent hoses. Notice the path they follow so you can put it back together right.
• Remove the vacuum advance hose from the left front carb holder and bracket.
• Unscrew the choke cable retaining screw enough to free the cable (Figure 2, A). Slide the cable housing out of the retainer. Unwind the cable and slide the cable-end out with the cable aligned with the slot in the lever. Do not use pliers (you'll fray the wire.)
• Remove the pull side throttle cable (Figure 3, B). It is the most outboard cable. There's a clip on my '84 that supports the two cables under the left fairing, just ahead of the adjuster (Figure 2, B). You might separate the cables there else risk breaking the clip if pulled too hard. Optionally loosen (screw all the way on) the lock nut and then adjuster for the pull cable (Figure 2, B) while carefully counting the turns so that accurate adjustment can be returned. This gives you a fraction of an inch extra play that I always seem to need. Pull the cable up and slide the cable through the slot in the inboard side of the cable retainer housing (Figures 2 & 3, C). Spinning the throttle wide open will help. You can now reach the cable-end and slide the free cable through the throttle-lever slot. This can be a bit frustrating. Maybe someone can help hold the throttle, etc. I also gently use the radiator hose pick to navigate the cable around. Again, never do anything that would fray these cables else you will need to replace it immediately.
• Loosen the four hose clamps on the carb holders in the same way as described per airbox. Free each carb from its holder rubber carefully and individually. I might use the radiator hose pick carefully to get this started. This is not a good place to have a vacuum leak by cracking, tearing, or puncturing a carb holder. Eventually the entire carb bank should begin to rock in the holders without a lot of restriction.
• Lift the carbs free from the holders and intake. Use a rocking motion and do not force. You may need to pry - gently - with a flat blade screw driver between the too of the carb holder and body of each carb to fully separate. Be careful not to damage the carb holders. Watch that cables and hoses on the right side of the bike are not interfering. Slide halfway out the left slide of the frame while watching that you are not crimping throttle or choke cables. The engine intakes are partially exposed, be careful nothing foreign can drop in there at this point.
• Remove the push side throttle cable as it is now more accessible.
• Remove the carbs and set them aside.
• Pack a clean rag or paper towels in each carb holder to plug the intake, the crankcase breather pipe, and/or cover everything to keep it clean! Allow nothing down the engine intakes. You can have a quick peek inside at the valves though.

Figure 2

Figure 3

Left/Right Carb Bank Disassembly:

If you need to access the fuel bowls to clean jets, float, float needle, etc., all you'll need to disassemble to access them is the left and right carb banks. You can also service the diaphragm (which can be accomplished with the carburetors on the bike), and the choke plungers and enrichment valves, although they will probably require separating the carbs individually.

• Disconnect the throttle linkage from the right carb pair. It is held by a C-clip (larger of the two, Figure 4, A) at the left carb bank end of the linkage (Figure 4, C). Figure 4 is left/right inverted as the carbs are flipped over.
• Disconnect the choke linkage by removing the C-clip on the right carb bank (Figure 4, D).
• Remove the screws from the two brackets (Figure 17) that hold the left and right carb banks together. They should be tight and probably will come out stubbornly. I might use a ratchet with a screwdriver tip, or a wrench or visegrip on the shaft of the screwdriver for extra leverage. Worst case, use visegrips as a wrench on the screwhead. Always replace any screws that get messed up.
• Separate the fuel distribution hose carefully from the right carb bank. If it is damaged it must be replaced.

Figure 4

If you plan to separate the carbs individually, mark the carbs per their respective position to avoid confusion at reassembly time. The choke linkages and spring arrangements are the only challenging parts to keep in order if you go that far. There is a nylon bushing in the carb and washer on the choke rod next to the individual choke plunger levers. Watch for the synchronizing springs which can fall free when you separate the carbs individually. Do one bank and one carb at a time and then reassemble them, just to avoid mixing up carbs and parts. Use Loctite on the choke lever screws (Figure 1, D, for example) and bracket screws when reassembling.

Jets and Float:

Work on one carburetor at a time. The work area should be very clean and dust-free. In these photos, everything is laying on paper towels, even though the bench is pretty clean.

Disconnect the fuel distribution hose from the carb you wish to work on. Remove the four screws from the back of the carb, the fuel bowl cover. You may need to tap the cover with the plastic end of a screwdriver to free it. Tilt and slip the cover away from the fuel inlet pipe while avoiding contact with the internal parts.

The inside of the fuel bowl is now exposed:

Figure 5

• Lift the float (Figure 5, A) off the hinge-pin (between Figure 5, A & B, also Figure 6, C) and carefully set aside on a clean surface. You can give it a shake and listen for any fuel inside of it - which there shouldn't be. Inspect for cracks or other damage. Any problems and you will need to repair or replace.
• Slide the float needle from the needle valve assembly (Figure 5 & 6, B). The needle and seat (contact areas of the needle valve) should be clean and not worn. The pin that protrudes from the float needle is spring-loaded and should move in and out freely.
• Remove the main jet nozzle screw, a large brass flat-blade screw (Figure 5, C). If the diaphragm is removed already, the main jet nozzle will drop through the other side. Underneath the screw is a flat washer. Put both the screw and washer off to the side.
• Remove the two jet block retaining screws (Figure 5, D). The jet-block should be able to come free, but straight up, if with a little coaxing. Do not tilt side-to-side as the main jet nozzle and needle are still underneath (Figure 6, between A & D). If it is stubborn, you can remove the diaphragm and nozzle from the opposite side of the carb, reducing risk of damage. Watch that the o-ring (Figure 6, D) is not stuck to the jet block, as it should stay with the main jet nozzle holder. The gasket may stay with the jet block or carb body. Do not disturb the gasket if possible, else it will need to be replaced - or if it is deteriorated. Also, watch out for the two rubber plugs (Figure 5, E) that go with the jet block.

The fuel bowl should now look like this:

Figure 6

The main jet nozzle holder is keyed into a slot in the carb body (Figure 6, D). There is an o-ring to seal between the jet block, carb body, and main nozzle holder. Remove and set aside (Figure 6, D). The only thing holding the nozzle in at this point is the diaphragm spring. You can remove the diaphragm now and the nozzle holder will drop out - gently, it is brass and easily damaged. You can now clean the bowl, float needle seat, and carb passageways. If the diaphragm is left in the carb, be careful when using strong chemicals or compressed air that you do not damage it. The fuel feed lines, bowl, and jet block should be cleaned well and dirt and crud free.

Jet Block:

The jet block has three brass jets (or nozzles), two of which (Figure 7, B and C) a covered by rubber plugs of two appropriate sizes. The jets can be removed for cleaning with a sturdy, narrow flat-blade screwdriver. The jets are soft (brass) and easily damaged. Take your time and make sure the blade stays seated in the slot, and they'll come out.

Figure 7

The jets are labeled in Figures 7 and 8:

A) Main Jet (see also near Figure 5, E)

B) Main Jet Pipe

C) Pilot Jet

Figure 8

The pilot jet is the most susceptible to contamination. It can be brushed clean by pushing a nylon bristle or something that won't scratch the brass, through the jet barrel. If the barrel of the jet is deformed, it will affect the air/fuel ratio or the carb. If a part is bad, replace it. Compressed air should be forced through the jets and jet block passageways to clear. A little carb cleaner sprayed in these passageways and jets can help dissolve heavy contamination. It would be a good idea to do the same to the carb body, but it is better to remove the diaphragm first (see below).

Clean the pilot air jet #1 (Figure 9, A) and the main air jet (Figure 9, B) at the inlet side of the carburetor's venturi. Blow compressed air through them with the jet block off, maybe some carb cleaner. Blow back through the jet block mounting surface and you should see unrestricted flow through the two hard-to-see ports in Figure 10, A & B. These might use some carb cleaner also. Clean the fuel bowl inlet pipes and the float needle's seat (Figure 6, B) are clean. A thorough job will require disassembly of everything in the instructions here, with compressed air blown through all the carb body's passageways.

Figure 9 


Figure 10

When reassembling the jet block, make sure the main jet nozzle holder key-way (Figure 6, D) is aligned with the jet block and seated all the way through the cab body. Check that o-ring (Figure 6, A) is lubricated and in place nicely. The jet block rubber plugs (Figure 5, E) should be clean and tight (flat edge to carb body). Use one finger between the diaphragm-slide and the jet nozzle holder to keep the nozzle holder in place as you install the retaining washer and screw (Figure 5, C). Tighten it with the jet block screws together and evenly. Check the condition of the bowl-cover's o-ring and that the surface it contacts is clean.

Diaphragms:

Diaphragms are easily done on the bike, or removed for service and carb body cleaning while on the bench.

• Remove the four cover screws (Figure 3). If one is a special Torx screw, you can buy a driver for it, or use visegrips as a wrench to unscrew it - and then replace with a standard phillips head.
• Remove the cover, while watching out for the spring behind it.
• Gently loosen the diaphragm from the carb body along the edges.
• Gently pull the diaphragm and slide with needle out of the carb.

Inspect the diaphragm for cracks and pin holes. Replace if damaged. Some people have reported success with various fixes, but remember that they are a huge part of the proper operation of the carb.

To disassemble the diaphragm, there is one white plastic screw centered inside. Under the screw is a spring, then washer, and then the needle assembly (needle, clip, small plastic retaining washer with a small pin to fit the slide). (Figure 11)

Figure 11

There are two air ports within the diaphragm area (Figure 12, C & B). Clean and blow compressed air though them. You can pull the pilot air jet #2 out (Figure 12, C) to better clean. This jet passes directly into the enricher diaphragm chamber, so it also should be disassembled before doing much with the jet - unless removed from the carb body. Don't loose track of the o-ring (Figure 12, B).

Figure 12

To reassemble, place the needle, washer, spring, and screw back into position, as show (Figure 11) in the slide. If your fingers won't fit, gently use needle-nose pliers. The needle has a plastic pin that fits into a hole at the base of the slide. This prevents it from rotating independently from the slide. By pulling lightly on the needle while rotating, it will fall into position. Tighten the plastic retaining screw firmly. Place the entire assembly back into the carb while guiding the needle carefully into the main jet nozzle.

Make sure the o-ring (Figure 12, B) is lubricated a bit and in place. The diaphragm has a tab on the perimeter (Figure 11, A) that fits into one spot on the carb body (Figure 12, A). Have the complete jet block installed if you removed it, then, starting with the tab, kind-of knead the perimeter of the diaphragm into the groove of the carb body so it stays in place. It should be willing to hold its position while you install the cover. Center the diaphragm spring over the three tabs in the cover, and slide into the diaphragm, slowly centering the cover onto the lip of the diaphragm and carb body. Make sure the diaphragm is not out of place before installing the screws. Diaphragms are easily damaged this way. Tighten the four screws evenly.

Choke Plunger:

The choke plungers can be cleaned and repaired without carburetor disassembly. You will need to separate the carburetors individually. They consist of a close tolerance brass piston valve and return spring, with a seal at the top (Figure 13).

Figure 13

First remove the actuator lock-screw (Figure 14, A). This will permit the actuator to rotate easily out of the way. Loosen the plunger retaining nut (Figure 14, B) and rotate the actuator arm away as you slide it out to remove the plunger, or if you plan on removing the choke body, remove the three screws (Figure 14, C for example) and the plunger will come out more easily on the bench.

Figure 14

Clean and blow all the ports thoroughly. Reassemble in reverse order. Lubricate the choke plunger shaft sparingly. Take care that the actuator is positioned to open the choke in sync with the other carburetor's choke that shares the same actuator rod. Adjust via bending the actuating lever (rarely necessary) (Figure 14, between A & B). Use Loctite on these screws.

Enrichment Valve:

The enrichment valve can be cleaned and inspected without carburetor disassembly. You will need to separate the carburetors individually. Three screws hold the small enrichment valve cover in place. A fairly strong spring with retainer cap is immediately underneath. To remove the diaphragm, you will need to carefully pick along the perimeter to free it from the sealing groove in the carb body (Figure 15).

Figure 15

The valve consists of a diaphragm with brass piston valve (obscured below) and a fairly strong spring with a spring retainer (Figure 16).

Figure 16

To reassemble, install the diaphragm working the perimeter into the carb body groove. A tab on the diaphragm (Figures 16, A) fits to seal the air port (Figures 15, A). The diaphragm should fit comfortably when extended inward to the carb body. The retainer fits into the spring, then onto the cover to maintain the spring's alignment. (I noticed in a later model I didn't see the small spring retainer cap, whether omitted by the PO or another wrench, or no longer used, I am not sure. There are some minor design changes after '83 which may omit them.) Carefully push the spring into the diaphragm spring retainer, and gradually push the cover closed while insuring the diaphragm remains in its groove. Tighten the cover screws evenly. Some of the covers use different length screws depending upon what else they are supporting, such as the choke cable.

Reassembly:

Put everything back together in reverse order. Make sure there is nothing that can contaminate fuel pipes or bowls - they should be spotless.

Loctite the screws that hold the hold the carb banks together. When tightening these brackets, place the carbs on a flat surface to make sure they are parallel and flat (Figure 17). If you disassembled the choke plunger lever, make sure the chokes open evenly per-bank and Loctite those screws (Figure 1, D).

Figure 17

If the choke plungers do not open evenly when comparing left-side to right-side carb banks, you can adjust by bending the rod between the two banks slightly to accommodate (in foreground, Figure 17). This will lengthen or shorten the throw of the rod to increase or delay the timing of the right bank in relation to the left. Use the choke cable attachment point to operate and base your judgments on. Absolute precision is not required, but it should be pretty close.

Attach the push throttle cable again with the carbs halfway in. Remove any rags/towels you installed in the carb holders to protect the intake. Make sure the carburetors are seated evenly and level in the intake holders, then tighten securely. Install the pull throttle cable and choke cable, and check their routing.

Check all hoses, vent pipes, and cable routing. Double check the throttle cable routing. On an '83 there is a retaining spring-clip to hold the cable end in place, fitting into a cable housing grove, although there is no location for it on my '84. There is a clip on my '84 that supports the two cables under the left fairing, just ahead of the adjuster (Figure 2, B).Almost for certain the cables have come loose from it. Finally check and re-adjust the throttle cable free-play. Make sure there is no binding in the cables and that the throttle snaps closed when released, regardless of handlebar position.

Check that the airbox boots are sealed into the airbox. Clean and reseal if necessary. Many silicone RTVs will not tolerate direct contact with gasoline, and although it is not literally direct contact, select a sealant/adhesive carefully. Make sure these boots are installed all the way around the venturi inlets before and again after tightening the clamps. Check that the crankcase vent pipe (Figure 2, A) is reattached and clamped (make sure you removed whatever you plugged it with.) Install the air filter and cover (it won't run well without them.)

Check that the fuel-bowl drain screws are closed and that the vent and fuel feed hose is attached properly, clamp tightened. Re-connect the battery and turn the key on and off a few times while listening to the fuel pump filling the fuel bowls. Look for leaks. If all looks good, fire it up. You will probably need to adjust the choke cable to get it operating the way you like again.

Check for any leaks again, then put the body back on and go for a ride to warm it up well. Adjust the idle and synchronize the carbs. You have changed the relationship of one carb to another, if just a bit, so a sync is probably necessary.

Go for a good ride! Hopefully whatever symptom brought you here is gone.

Last update: 08:39 PM Thursday, November 16, 2006

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