QuestionI have a 1988 Kawasaki ninja zx600, and I have a few problems with it but i'll just ask this one question. I can't seem to get fuel to pass from the gas tank to the carbs. I have a clear 'see through' fuel line so I can see if fuel is being vacuumed from the petcock to the carbs.
Here are a few things I did to test what was wrong.
1. I wanted to test the fuel petcock first, so I disconnnected the fuel line from the petcock. I connected a new clear fuel line to the petcock and put the other end of that line into my mouth and used my mouth as a vacuum to suck out the fuel to see if it would come out. And yes the fuel flowed out just fine.
2. Next, my fuel petcock has two outlets (connections) on it. One sticks out straight to the right which I know is for the fuel line. Which I tested in step 1 above. And the second outlet is underneath the petcock and points straight south. I don't know much about motorcycles but im assuming it's used as part of the vacuum process, maybe? Anyways I connected a clear fuel line to that also and used my mouth at the other end of it as a vacuum "sucked". Which in turn caused fuel to start coming out of the fuel outlet on the right side of the petcock. So it seems to me like the petcock is working fine.
3. Next, I removed the gas tank and focused on the carbs. I went ahead and filled my carbs with gas using the fuel line connected to the carbs and a funnel. I have an inline filter installed by the way. So with my carbs filled I started my motorcycle and its starts fine. It will keep running until the carbs run out of gas or I can keep filling them with a funnel. So my motorcycle seems to run.
4. So i put the gas tank back on and connected the fuel line to the carbs. Now im not sure where the outlet underneath the petcock pointing straight south is suppossed to be connected to. Now my carbs (I have 4) each have an outlet or inlet(not sure what they do) pointing straight up and near the top of each carb. A tube or hose can fit on each of these but for now I have nothing connected to them. Anyways the same size tube or hose that can be connected on the south outlet underneath the petcock can also fit to any of the 4 outlet/inlet connections near the top of my carbs that I just mentioned. Again like I said I don't know what any of these extra outlets/inlets on the carbs and petcock are for. So I leave them as so, they are not connected to anything. Next, I start the motorcycle and it runs(of course until the carbs run out of gas). So while the motorcycle is running and before the carbs run out of gas I look to see if fuel is getting pumped from the petcock to the carbs, and NO fuel is getting pumped. So while the motorcycle is still running I connect a tube to the outlet underneath the fuel petcock thats pointing straight south and use my mouth as a vacuum again(because it worked before in step 2). But it doesn't really work this time. It seems to trickle out very slowly, if not at all. I don't understand.
So in short im assuming it has to do something with the vacuum between the petcock and carbs. I guess I have an air leak somewhere or some bad hoses.
Please Help!
Thanks Andrew
AnswerHi Andrew,
Very well written description. Thanks!
The petcock seems to be working properly. The larger outlet pointing to the side (East/West) is the fuel outlet pipe. The smaller outlet pointing South is the vacuum hose pipe.
Connect a hose from the #2 carb's vacuum pipe and connect the other end to the petcock's vacuum pipe. Plug or cap the other carb vacuum pipes. This is an air leak and will cause performance propblems if left open.
Connect a fuel rated fuel hose to the fuel pipe.
If gas is reluctant to flow, inspect the fuel tank/cap vent for obstructions.
Keep in mind that fine rust particles pass right thru most fuel filters. Check tank for evidence of rust. Seal with "Red-Kote" if necessary.
Review the tech files below. Clean the carburetors if necessary.
Respectfully,
Mark Shively
Bad Gas
Gasoline goes bad with time and in as little as 3-4 weeks. This effect is known as varnishing. Jets and passageways within carbs become obstructed when varnishing occurs.
Liquid gasoline changes chemically into a gel like substance. Advanced stages of varnishing results with the solid gel changing into a crystal powder substance. Interior carb surfaces are etched in the process and may require carb replacement.
The choke and pilot circuits with most motorcycle carburetors share passageways. When pilot jets become obstructed, the choke circuit compensates and allows engine to start and idle with choke, but stalls without choke.
See carb cleaning information file below. See microfiche parts, check parts prices, and order repair manuals here: www.bikebandit.com
Carb Cleaning 101
By M. Shively
The elements of internal combustion engines are: correct fuel/air ratio, spark at right time, adequate cylinder compression.
There are many passageways and openings to check and clean. All are important in function and when obstructed or not working properly, have subtle to radical effects on engine performance. Vacuum leaks and carburetor synchronization also have effects on performance and should be inspected and adjusted following the below procedures.
Carb Cleaning 101
Warning: Remove all rubber parts before you begin. These parts usually include vacuum diaphragms, needle valves, o'rings, hoses, and other parts. Spray cleaners will damage these parts. Do not disassemble individual carbs from the carb bracket.
Air & Fuel Passageways: Trace and learn individual fuel and air circuits from beginning to end. Machines can only drill straight through the cast passageways. To change direction, another angled passageway must be drilled. The union is plugged with a brass or bronze bead. Inspect and clean each passageway with spray cleaner, brushes/pipe cleaners/etc, and compressed air. Remove any discoloration and debris. Look for spray cleaner to exit from one or more passageways.
Jet Cleaning: Inspect jets by holding to light and look through them. You should see an unobstructed round hole. Clean the jets with one or more of the following: jet cleaning wires, soak solutions, carb spray cleaners and compressed air. Re-inspect jets after cleaning and install when clear of obstructions. Some main jets have paper-like gaskets. Most have metal spacers between the jet and the emulsion tube. Some screw directly into a brass emulsion tube which is machined for a 7mm wrench at its float chamber exposed base.
Inlet Fuel Valve: Inspect the needle valve & spring. Press down the tiny metal rod that protrudes from the butt or float end of the needle valve. The spring should move freely and return the rod to its location. Check the needle valve's seat area for a groove or other wear. It should appear highly polished. Some needle valve seats are rubber and wear may not be visible. Inspect the needle valve jet seat. You can clean the jet seat with Q-tips and semi-chrome polish if necessary.
Carb Body Castings: Blow air through the atmospheric vent holes located on the dome of each float bowl chamber. Air should exit via hoses or brass nipples. Inspect the emulsion tubes and passageways (cast towers that jets thread into) for discoloration and debris. Clean interior emulsion towers with a soft bristle gun cleaning brush. Clean each Venturi (main carb bore).
Needle Jets & Jet Needles: Clean the needle jets, jet needles, and passageway or tower that needle jet screws into. Clean the emulsion tube (pipe between needle jet and main jet) (Main Jet may screw into emulsion tube). Jet needles are part of the throttle slides. See below…
Throttle Slides: There are several types of throttle slides: Mechanical linkage, vacuum, diaphragm, and cable. Disassembling the jet needle from the slide is not always required for cleaning. If you have vacuum piston type throttle slides (large diameter solid metal slide), avoid cleaning the lubrication from sides and caps. If piston type check cap vents and passageways with air. Clean if necessary and re-lube. If you have rubber vacuum throttle diaphragms, inspect for dry-rot, defects, and tears by gently stretching rubber away from center. Do this until all areas around diaphragm have been inspected. Replace any defective part as described above. Clean carb body areas around diaphragm including air passageways and air jets. Diaphragms have a locator loop or tab fabricated into their sealing edge. Observe this locator upon reassembly. Avoid pinching the diaphragm when reinstalling caps.
Fuel Screws: Fuel screws have sharp tapered ends. Carefully turn one fuel screw in while counting the turns until it seats lightly. Warning: These screws are very easily damaged if over tightened into their seats. Record amount of "turns-in" and remove the fuel screw, spring, washer, and o'ring. The fuel screw is part of the enrichment (choke) circuit...clean passageways as described above. When carbs are assembled, spray low PSI compressed air into diaphragm air vents located at intake side of carbs. Throttle slides should rise, then fall when air is removed. Lightly lube external moving linkages. Reinstall carbs and follow through with carburetor synchronization.
Throttle Cables: Lubricate cables periodically. If cables are disconnected from carbs or removed for replacement, etc . . . remember cable routing and ensure proper reinstallation routing. Avoid bread-tying, sharp bends, and pinching cables. Adjust cables so throttle grip has about 5mm of play or throttle slides or butterfly valves may not open completely (full throttle)(wide full open).
Float Bowls: Inspect float bowls for sediment, gum or varnish, crystallization, and defects. Clean all pipes, tubes, passageways, and embedded jets with cleaners and compressed air. Remove and clean the drain screw and area. Inspect bowl gasket and replace if necessary. Clean and inspect overflow pipes and tubes, look for vertical cracks.
Floats: There are several types of float materials: plastic, brass, black composite, tin, and others. Handle floats carefully. Avoid bending, twisting, denting, or other means of mishandling. Most floats are adjustable by bending a small metal tab near the float axle end. Do not change the float adjuster tab unless tuning fuel service levels. Clean metal floats by soaking or by spraying cleaner and wiping clean. Other material type floats may require replacement if cleaning is necessary. Inspect the needle valve (float valve) and seat. Check needle valve's spring loaded pin. It should depress and return smoothly and without resistance. Check the needle valve's tip for a worn groove. Replace needle valve and seat if either symptom exists. These parts wear together and must be replaced as a set.
Synchronization: This is a fine adjustment performed usually and preferably with the carbs installed and the engine running. The unusual part is performed with gauged wire with the carbs on the work bench. Carburetor synchronizing balances Venturi vacuum at the exhaust side of each carburetor, resulting with smooth idling and optimized performance at all throttle openings. Synchronization is checked using a set of gauges which are either air vacuum type or liquid mercury type. The gauges are connected to vacuum ports on the intake manifolds via nipple tubes or if sealed with screws, sync gauge adapters will be needed. With the engine running at temperature, and with a fan or means of forced convection aimed onto the engine, the carbs fuel screws and idle are adjusted, then the synchronization is adjusted via adjustment screws on the carbs. A reserve fuel tank is recommended for convenience of accessing carbs during this procedure. See gauge instructions and repair manuals for detailed use of synchronization gauges.
Notes: While carbs are apart, record the jet sizes. Look for a very small number imprinted on the body of the jets. Verify that numbers are the same for all jets on models with in-line cylinders. A few transverse-4 models and V-engines, the inner and outer carbs use some different size jets and it's important to not mix them up. If you have dial or veneer calipers, measure and record float heights. Perform measurements with floats just touching needle valves, though not depressing the needle valve rods. Replace fuel and vacuum hoses. Be sure to use fuel rated hose for fuel. Install or replace in-line fuel filters. It's a good time to remove and clean interior petcock fuel filters. Inspect carb manifolds for dry-rotting, inspect all clamps and air ducts. Inspect, clean, lube, and/or replace air filter(s).
