QuestionI just bougth a used 2005 Yamaha XT-225 Dual-sport. 185 Miles on it. It dies at low RPM unless I pull the choke out then it revs very high. If I get it up to speed 40 mph or greater I can shut the choke off and it seems to run pretty good. Not sure what's going on here. The first day I got it it ran great. I have replaced all the fuel in the tank and cleaned the air cleaner. Seems as if it's a carb problem. Plug looks fine. I did wash it and it fell over on the driveway. I started it after washing and it for a couple of minutes to dry things out seemed to run ok then but now seems as if everything went down hill after that. Cant figure out why it would run great one day and a week later run like crap! Thanks for any help! PS- I think this bike is known to have some crab related issues.
AnswerHi Bob,
The carburetors will need thoroughly cleaned. The entire fuel system should be inspected, cleaned, or repaired accordingly.
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.
Motorcycle and ATV carburetors have many passageways and openings to check and clean. Subtle to radical effects on engine performance occur when jets and passageways become obstructed. Vacuum leaks and carburetor synchronization also effect performance and should be checked and adjusted. The following procedures are a helpful guideline.
Carb Cleaning 101
Warning: Remove all rubber (Neoprene) parts before applying chemicals to carburetor parts. These parts usually include vacuum diaphragms, needle valves, o’rings, hoses, and other parts. Spray cleaners may damage these parts. Do not disassemble individual carbs from the carb brackets.
Air & Fuel Passageways: Trace individual fuel and air circuit passageways from beginning to end. Machines can only drill straight paths through castings to form passageways. A change of direction or angle means drilling additional connecting passageways. Access holes left by the drilling process are plugged with brass or bronze beads. Inspect and clean each passageway with spray cleaner, brushes, pipe cleaners, and compressed air. Many household items can be useful cleaning tools. Remove any discoloration and debris from carbs. Look for carb spray cleaner to exit from one or more passageways. Chase immediately with compressed air.
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 emulsion tower (main 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 tip for a worn groove. Replace needle valve and seat if either symptom exists. The valve and valve seat wears 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 workbench. 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. Gauge sets are available in air vacuum type, liquid mercury type, and steel rod type. The Morgan Carb Tuner II is the most accurate tool in my opinion. Mercury vapors are toxic and Mercury is a hazardous material. 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. It is important to note jets sizes and locations. 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).
