 Techline-Nov09-A TACH, A STUMBLE, AND A CLICK-Part II-Cont.
This article concludes in the next thread.
Whether the vapors vent to outside atmosphere, to the rear of the engine, or to a charcoal canister to be purged and burned in the combustion chamber, they must go through the vapor valve. Following the fuel tank evaporative (vapor) hose will always lead you to this small black plastic valve. The vapor valve is another one-way regulating device with an internal ball and seat arrangement; at least that is what it sounds like when shaken.
The 2-1/2"-long, durable, black plastic vapor valve is a sealed unit that looks similar to a gas filter, except there is no way to see what’s going on inside. The upper 1/2"-long, 3/16"-diameter nipple-feed inlet is designed for a 1/4" flexible hose. A wider, 1/4"-diameter protrusion extends down 1/2" and houses a needle/ball and seat apparatus. Next, the body that houses the valve weight arrangement is 3/4" in diameter and at its widest point is about 7/8" long. From this extends an identical, lower, 1/2"-long, 3/16"-diameter nipple for a 1/4"-hose fitment. One nipple end connects to a flexible hose that extends to the fuel tank standpipe. The other nipple connects to a hose that directs evaporate away from the hot engine, causing exhaust to dissipate into the atmosphere on 49-state motorcycles and into the charcoal canister on CARB bikes.
I thought I would find a simple ball bearing that would rest in a seat, much like the system in pre-1999 oil pumps that is supposed to prevent gravity feed of oil into the bottom end when the bike is at rest. I could not contain myself, so I cut one open to find a much more sophisticated, spring weight-activated seat and needle system. A light spring sits underneath the weight, which sits under a guide. The guide sits inside the needle on top. The needle is similar to one found in a carburetor float bowl. However, this needle can settle into its respective seat that is part of the plastic housing even if the vapor valve is turned on its side or is upside down. The longer portion of the vapor valve must face vertical (upward) to function correctly. When on its side, the spring can close the needle valve on its seat. If upside down, the weight will take over and firmly close the needle into its seat. In these last two situations neither gasoline nor evaporate can escape the vapor valve. This obvious safety measure will prevent a potential fire hazard during an accident or when the bike tips over. It also limits minor environmental pollution.
Continuous Venting
Physics 101 dictates that gas tanks need to vent air in to replace evacuating fuel or the ensuing vacuum will prevent fuel flow to the carburetor. Expanding gas fumes also need to vent or gas may pass by a weakened carburetor float mechanism, which controls the flow of gas into the carburetor while ensuring there is a steady supply on hand. The 40mm Keihin CV carburetor necessitated the development of continuous venting of the gas tank to ensure a constant fuel supply. Is this development too simple to mention? Try riding a bike with venting issues. The experience will be aggravating to say the least, and the ride nonproductive. At first glance, one would think that these parts are in upside down since gravity prevents the needle from mating with the seat on top of it. It is exactly as designed. The fuel vapors and vented crankcase oil vapors need to flow past the needle-and-seat arrangement at will when the bike is upright, so they can dissipate into the air behind the engine and away from the hot exhaust pipes or safely into the California emissions charcoal canister.
If the bike falls over, the weight of gravity will press against the needle guide, pushing the needle into its seat. The vapor valve will block liquid gasoline flowing out of the gas tank from continuing any farther through the vent vapor tube. If installed upside down by an errant mechanic, or if its bracket fails to secure it in its proper upward position, the valve and seat will prevent vapor from going through the valve. This can result in an excessive buildup of vapor in the gas tank. If the vapor cannot find another way to escape and equalize pressure, then excessive pressure buildup in the gas tank can force fuel down into the carburetor.
Normally, the carb’s float mechanism will stop excessive flow and act as a dam against more fuel coming into the carburetor. A float is an airtight, hollowed-out, doughnut-shaped apparatus made from light and thin brass. Some aftermarket ones are solid, made from a nonporous, light material that floats in a liquid. The float regulates the flow of gasoline into the float bowl. The attached needle regulates the float’s preset level. The factory or a mechanic adjusting the float level usually does so by bending the protruding thin metal tab that attaches to the needle. This mechanism keeps a reservoir of gas at the ready, so it can be drawn up into the carburetor venturi via the low pressure created by air moving through the venturi. As gas is drawn up, the float lowers, lifting the needle out of its seat, allowing more gas to enter, via the force of gravity, to fill the reservoir (float bowl). Once the float reaches the preset level, it prevents more gas from entering the bowl by forcing the needle down into its seat in the fuel inlet fitting.
Vapor Valve Bracket Recall
Service Bulletin M-1093, Safety Recall Code #01011, concerning the vapor valve involves bracketry that fails to stabilize it in the up-and-down position. The defective bracket may allow the vapor valve to tilt to the point of allowing the vapor needle to close on its mating seat, thereby blocking evaporates from properly venting. This could cause the engine to quit or stall when still in an upright position. A buildup of vapor in the gas tank will put downward pressure on the gasoline, perhaps forcing it down into the carburetor below, overwhelming the float mechanism, and pouring raw gasoline into the engine and out the float vent. Raw gas does not burn and will cause the spark plugs to foul with a flat-black, fluffy residue, which insulates the electrodes. When this happens, the spark cannot jump across the gap to ignite the air/fuel mixture, thereby stalling the engine.
The float vent is a small hole drilled into the carburetor body above the maximum float setting. Gas runs out of this hole, and down onto the engine in early Harleys or into a vent/overflow tube on subsequent models that directs the gas away from the hot engine or exhaust pipes. The vent tube may also attach to a fitting above the float bowl setting on some carburetors like the Keihin CV, which has a standpipe that protrudes from the bottom of the float bowl, up through the gasoline, past the float.
The vent hose on modern Harleys will run into the carburetor backing plate so that vapor can burn off. Of course, any amount of gasoline flowing through this vent will foul the plugs and prevent the engine from running. On EFI models, the pressure will build up in the gas tank, but will not overwhelm the fuel pump that delivers the fuel to the injectors. Buildups above atmospheric pressure will always seek out the weakest sealing link and eventually escape, perhaps causing part damage. Certainly, seals will wear prematurely. Leaking vapor near hot parts is always a safety concern. Fortunately, once the motorcycle is in motion, flowing air will usually disperse any vapor safely.
The whole point of the recall is to bracket the vapor valve securely in its upright and correct position. This was really the second recall issued regarding venting on late Evos and early Twin Cams.
Blocked Vent Recall
Most venting problems involve a kinked vent hose or a blocked vent. However, the two recalls issued with the advent of the Twin Cams and affecting late Evolutions required a little more detective work than normal, as they were manufacturing missteps. This is not as strange as it may sound. H-D production really divides into half years. New design changes for the following year are many times introduced in the last half-year production of the previous year. This particular one bridges the change to a new powertrain.
The first Service Bulletin M-1085, Safety Recall Code #098, issued on August 4, 1999, was a follow-up to Service Bulletin ML-366 and applies to 49-state FXRs, Dynas, and Softails built between April 27, 1999 and June 6, 1999. It involves a possibly plugged gas tank vent line connector (#61131-92) that fits into a frame member so that the secondary vent hose from the vapor valve can feed fumes inside the frame for safe dissipation through the hollow frame members and into the atmosphere out uncapped ends, away from hot components. The carburetor overflow hole on these models is the standpipe protruding up through the gas from the base of the float bowl. If gas flows out this standpipe hole and eventually onto a hot engine via the air cleaner, safety certainly becomes a concern. It’s likely that this condition can result in overflow gas from the carburetor.
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