Question My son just bought a USED, 2002 SUZUKI Katana 600 with only 2650 miles 4 days ago. Easy Start and Runs Great! However the problem starts when it's put up after riding. It starts to LEAK GAS 4-5 hours after its parked [Not Running]. To me it sounds like the FLOAT(s) may not be working as they should. My son and I will look at it this weekend and I just thought I'd see if you had any other idea's. It didn't leak gas until I, that's right ME, DA', left the FUEL SWITCH on "PRI" a couple nights back! Every since it starting Leaking as stated.
Thanks and Ride Safe!
-TJ-
AnswerHi TJ,
You're pretty funny [smiling]. I appreciate the humor.
The fuel head pressure can be too great and overcome the float's pressure on the needle valves. In this case the bowls may over flow
For the record...
PRI= Prime; For refilling the float bowls after servicing the carburetors. The vacuum side of petcock is by-passed to allow fuel to flow when the engine is not running.
RES= Reserve; Enough petrol to get our butts to a refueling station. Vacuum operated, works only with engine running.
ON= On; the primary operating position. Vacuum operated, works only with engine running.
If you must use PRI to ride, replace or repair the petcock.
The problem may be one or more of the following:
Worn needle valve sets.
Varnished needle valves springs/pins.
Worn or defective floats.
Worn or defective float bowl seals.
Cracked float bowl over flow tubes.
Improperly adjusted float heights (fuel service levels).
Worn or defective fuel supply line.
Defective petcock/diaphragm.
I've pasted a couple of tech files below for your convenience. Sorry! You won't be able to view the images. I return tech files be email. There was no email address with your question as requested and explained in my instructions.
Respectfully,
Mark Shively
Bad Gas
By Mark Shively
Gasoline goes bad with time and in as little as 3-4 weeks. This effect is known as varnishing. Jets and passageways within carburetors 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. Learn more about cleaning carburetors, review the information below. Order Service Manuals (repair manuals) here: www.repairmanuals.com View microfiche parts and check part prices 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.
Needle Valves: Inspect the needle valve and its interior 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. The spring is internal, however still exposed to fuel. Fuel often varnishes around the spring resulting with float failure and overfilling of the float bowls. A good indication of varnished, worn or defective needle valves is fuel in the airbox, fuel on the ground, and fuel in the crankcase. Check the needle valve’s seat area for a groove or other wear. It should appear highly polished. Some needle valve seats are a rubber (Neoprene) material and wear may not be visible. Others are precision machined metal surfaces and are usually polished. Inspect the needle valve jet seat. Clean the needle jet seat with Q-tips and metal 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 passageways or towers that needle jets screw into. Clean the emulsion tubes (pipes between needle jets and main jets) (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.
Choke Plungers: It is common for Mikuni slide carburetors to have indented or hardened choke plunger pads. If the pads are worn, indented or hardened with age, then the idle of your bike will vary wildly as the pads no longer seal well.
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 vernier 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).
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Servicing the Petcock
The Petcock is quite simple in its construction and operation. A correctly operating petcock will only allow fuel to flow when vacuum is applied (small hose attached) no matter what position the petcock is in. The "Off" position will not allow fuel to pass even with vacuum. This allows removing most of the fuel from the bowls, if needed, by letting the bike burn it off while running. However, for storage purposes I’d go a step further and use the drain plug at the bottom of each bowl. My other bike does not have an "OFF" position but rather a "Prime" or always on position. All vacuum operated petcocks operate basically the same. PRI or Prime is used to refill the float bowls following servicing the carburetors.
Once you get the tank off set it down on something soft. Pickup the rear and roll it up on its nose. It will sit there and allow you to remove the petcock without spilling gas. However, when you set the tank back down flat hold your finger over the vent tube or gas will begin to siphon out.
Remove the petcock by loosening the flange nut. Carefully pull the petcock out. You’ll see the fuel screen attached, which is in two sections; one for "On" and the lower portion for "Res." To clean this part use basic carb cleaner or contact cleaner. Just be careful with the screen, its very delicate.
The rest of the petcock is made up of three sections. The 1st is the main unit which has the screen attached. The 2nd and 3rd pieces are attached to the main section with 4 Phillips screws. The outer section is just a cover. The middle section holds the diaphragm. Notice that this section has a small nipple protruding which has a hole in the center. This is a check valve. Remember which direction this is facing in relationship to the main section. There is a spring between the cover and diaphragm. This spring pushes the diaphragm back when vacuum is released and prevents fuel from flowing. Also note when you pull the cover off and remove the spring. The rubber diaphragm’s larger section faces outward.
Clean everything with your cleaner and reassemble. Make sure you VERY carefully pull the ends of the diaphragm up and clean behind and between the folds. If for any reason the middle section will not pull away from the main section DO NOT force it. It simply means your check valve is plugged and vacuum is holding it on. That’s why when you disconnected your fuel line, gas may have continued to flow until you turned your petcock to the "Off" position. Carefully lift up on the end of the diaphragm to release pressure.
Now that it is all back together. Its time to test it to ensure it works properly and won’t require pulling the tank back off later. Simply attach a clean rubber hose onto the vacuum nipple. Apply a slight vacuum to the hose while looking down the fuel outlet. Yes, your mouth works great for this. As you apply vacuum/suction you’ll see the diaphragm pull away from the main section. When you release vacuum/suction the diaphragm will SLOWLY return sealing off the flow of fuel. If it doesn’t, either you assembled incorrectly or your check valve is still clogged or defective. If all works, you’re done!
Courtesy of: Chuck B
