Question99 KZ1000 p stalls when motor warm. I have newly done a total carb rebuild, plugs, wires, valve adjustment and a carb sync. It starts well and runs very nice. I did the work due to this stalling which persists after repairs. After an easy start I go to disengage the clutch and the motor instantly stalls, only to start easily after I reengage the clutch. This goes on repeatedly until it finally will run. This is happening less than before the rebuild. Starts well cold with no stalling. Any thoughts?
AnswerHi Gary,
I suspect a clutch adjustment problem or worn clutch plates/springs. I would need to perform a few checks to accurately diagnose the problem.
Respectfully,
Mark Shively
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).
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Clutch Operation Faulty
Clutch slipping:
No clutch lever play
Friction plate worn or warped
Steel plate worn or warped
Clutch spring broken or weak
Clutch release mechanism trouble
Clutch hub or housing unevenly worn
Clutch inner cable catching
Clutch not disengaging properly:
Clutch lever play excessive
Clutch plate warped or too rough
Clutch spring compression uneven
Engine oil deteriorated
Engine oil viscosity too high
Engine oil level too high
Clutch housing frozen on drive shaft
Clutch release mechanism trouble
Clutch hub locknut loose
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Definitions
Pressure Plate – The moving part of the clutch assembly that working against clutch spring tension, releases the clamping action on the clutch plates when the clutch lever is engaged.
Drive (friction) Plate – Consumable, fiber coated, ring-shaped friction surface that interfaces between the clutch basket tangs and pressure plate. Has tabs sticking out that match the cutouts between the clutch hub tangs and is coated with a friction material that vaguely resembles brake pad compound.
Driven (metal) Plate - Steel or aluminum ring-shaped disks that interface between the clutch hub and the friction plates. Steel plates are most often found in enduro/trail machines and provide longer wear and greater flywheel effect. Aluminum driven plates, near universally found in motocross type machines, are lighter, less durable and provide less flywheel effect. Additionally, aluminum driven plates wear out nearly as quickly as the friction plates themselves, in the process fouling transmission oil at an accelerated pace.
Clutch Springs – Short coil springs that continuously hold the drive and driven plates together through spring tension. Their duty is preventing slippage except when the clutch lever is engaged. Most often, five or more clutch springs are used per motorcycle clutch assembly. Firmer rated springs or more springs are typical of performance engines. Softer rate or fewer springs requires less clutch lever pulling effort.
Clutch Basket – A bowl-shaped gear-driven housing bolted onto the end of the clutch shaft that holds the entire clutch assembly.
Clutch Basket Servicing Procedure
Begin by either draining the motor's transmission oil, or lay a small bike over on its side, ISDE style (clutch side up). With the bike on its side, the oil doesn't need to be drained as it pools below the level of the clutch side cover. Next, remove clutch cover (on bikes so equipped) or the entire clutch side engine cover in order to expose the clutch basket. If the entire side cover must be removed, the kick starter, shifter and/or brake pedal might have to be removed first, depending upon the bike make and model (get a manual). Some models might even require the draining of engine coolant and/or disconnection of power valve linkage. Pray that your scoot has a clutch cover. With the clutch basket exposed, loosen the five or six fasteners on the face of the pressure plate that compress the clutch springs. In most cases M6-sized fasteners are used, most commonly shod with 10mm hex heads. On occasion you'll find an 8mm hex head or socket head (KTM) fastener. No matter which, back these bolts out evenly, a little at a time, alternating fasteners back and forth across the clutch basket. If the entire assembly has the tendency spin, drop the bike into gear to prevent this. With all of these fasteners completely loosened, lift out each bolt, washer and clutch spring and set them aside some place where they'll stay clean. Measure the free length of the clutch springs and compare that to the specification for minimum free length listed in your service manual. If the clutch springs have sagged, (insufficient minimum free length), they'll need to be replaced. With pressure plate retaining fasteners removed, the pressure, friction and driven plates may now be lifted out of the clutch basket. Remove the pressure plate first and set it aside with the clutch springs, someplace where it won't get dirty. When removing the pressure plate, be careful with the clutch actuation rod. Oftentimes there is a flat needle bearing, spacer, or even a simple ball bearing, that can drop out and become lost. Be sure to pay attention to the order in which these parts go back together. Be advised that for a basic clutch plate replacement, removal of the clutch actuation rod probably isn't necessary. However, while you've got things apart it's not a bad idea to check the rod for wear or bending, especially if clutch action has been faulty. Just be sure not to lose any of these small parts or forget how they came apart. Now it's time to lift out the friction and driven plates. Friction plates sometimes have the tendency to stick together, or even stick to the clutch basket face. A screwdriver or other prying tool can be carefully used to break the slight stiction holding them together. Be careful not to score clutch basket or clutch plate faces and stop immediately if they don't come readily apart—something must be wrong if that's the case, and you'll need to seek higher guidance. With all clutch plates removed, inspect the clutch basket, looking for grooves worn into the basket fingers or scoring on the face. Grooving adversely impacts clutch actuation effort and smoothness. If the clutch basket fingers are grooved more than, say, 1/32nd of an inch or so, they'll need attention. In extreme cases, the only option is replacing the clutch basket. However, if the grooving is less serious, they can be smoothed out using a hand file. Bear in mind though, this creates more slop in the clutch actuation, so that next time the grooving is likely to be considerably worse. Essentially, it's a temporary fix that buys you some additional riding time. Note that the clutch basket rides on one or two thin needle bearings. If you're forced to replace the clutch basket, its prudent to change this needle bearing as well. With all that out of the way, we can begin to reassemble things. If you're just replacing the friction plates, separate out the old friction plates from the driven plates. To replace the clutch, restack the new plates inside the clutch basket alternating friction plate/driven plate. A friction plate always goes in first, and as such all clutch assemblies always have one more fiber plate than metal plate. Be sure that a fiber plate is the last plate that goes in on the top of the stack as well. Do not stack the plates together dry—coat all of them with transmission oil before you stack them together, or you'll burn the clutch up the first time you ride the bike. If your bike is equipped with aluminum driven plates, its highly recommended that they be replaced, or at least checked during the replacement process. Again, your service manual will have a thickness specification for both friction and driven plates. If you're using your scoot for off-road racing or trail riding, we'd highly recommend you consider replacing aluminum driven plates with aftermarket steel ones. This switch offers three potential benefits to the typical off-road set: Better driven plate longevity (read: forever), less fouling of transmission oil, and greater flywheel effect. Continue the reassembly process by dropping in the pressure plate. Check your service manual, since some bikes require marks on the pressure plate and clutch basket to be lined up on reassembly. Begin to tighten it down by replacing the clutch springs and their fasteners. Be sure to start these bolts by hand to avoid cross threading them and hosing the clutch hub. Tighten them down evenly, alternating bolts in a cross wise manner. These bolts don't get torqued very much, so be sure not to manhandle or over-tighten them. There's a torque spec in your owners manual—use it. Complete the task by replacing the clutch cover or side cover with fresh gaskets. If you drained your oil, be sure to replace it with the proper amount of fresh transmission lubricant. We use Golden Spectro SAE 80w motorcycle gear lubricant in our two stroke gear boxes. In a four-stroke engine, remember to use a 10w40 or better motor oil rather than gear lubricant.
