QuestionI have a 2000 Susuki DRZ400, enduro which will not accelerate. It boggs out and backfires. I had a needle and seat put in about 3 months ago at the dealer. The dealer is now telling me that my gas is old and I need the carburator cleaned. I did this myself and put new gas in and it still does the same thing.
Please help!
Thank you,
Dale Warby
AnswerHi Dale,
I suspect the jet needle may be the wrong part or adjusted improperly. (There may some form of intake air restriction, too.) Delaers seem to blow customers off easily. One of the reasons I do this volunteer service with AllExperts.
Try lowering the jet needle clip one notch. Re-install carb top and perform test ride. Make one carb adjustment at a time and test ride after each adjustment. This is tedious work, but it's how it's done properly.
Send me your email address. I'll send carburetor tuning information files that will assist you. A sample carb file is below. My email addy is: mshively1@woh.rr.com
Use the following websites as a reference to see microfiche parts online: "www.bikebandit.com" (click on OEM Parts, enter vehicle info), and "www.mikuni.com/fs-carburetor.html" (look at RS Series carburetors).
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, orings, 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 the Venturi's (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 oring. 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 spray cleaners, if necessary. Replace other type floats if cleaning is necessary. Clean the float axle or pin.
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. It should be the same number for all. 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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TUNING THE SLIDE-TYPE MOTORCYCLE CARBURETOR
Pete Snidal, (C) 2000
Whether it's an Amal, - Standard, Monolbloc, Concentric, TT, or GP - or a Del'Orto, Mikuni, or Micarb, there's a same-ness about slide-type carburetors as found on motorcycles built during the past 60 years and more. Air is admitted into the intake tract by means of raising a slide in the body of the carburetor, and consequently raising a fuel control needle attached to, and usually inside, the slide.
Fuel is maintained at a constant level in an adjacent float chamber, usually part of the carburetor body, by means of a float and valve arrangement, and is admitted into the airflow beneath the slide through a series of jets, the most important of these being the needle jet - the one the tapered needle slides in when the slide is moved. The size of this jet, the taper, and relative position of the needle are the determining factors for mixture (air/fuel ratio) in the range of 1/4 to 3/4 throttle, give or take. Once the throttle is above 3/4, the needle jet passes pretty well all the fuel that comes its way. It is regulated only by the size of the restriction below the needle jet, which is the main jet. Changing the size of this jet thus controls mixture at the "top end" of the throttle, and to an extent, the rpm range. (Since mixture is dependent to a degree on airflow, the upper end of the throttle range wants to be tuned at the upper end of the operating rpm range.
To set the jetting for either of these ranges, we do a "plug chop." The tip of the spark plug insulator changes colour with mixture - a white tip shows too lean a mixture, a black one, too rich. The ideal is just the sandy side of chocolate brown.
To do a plug reading, you want to run at 1/2 throttle for a minute or so, pulling upwind or up a hill, say, and then suddenly hit the neutral finder, if so equipped, or pull in the clutch, and turn of the key, coasting to a stop at the side of the road. Where you take the plug wrench out of your pocket, and pull out the plug and have a look. White plug: clip down, black plug: clip up.
For Main Jet tuning, repeat as above, but at full throttle. White plug: bigger jet, black plug: smaller jet. If it won't get up onto full throttle because of bucking and missing, you have to look at your pipe and if you see black smoke, you know it's 'way too big, so you'll have to try a smaller one. If it's too small, you'll get a white plug tip on full throttle, if not a lot of starving, bucking, missing, spitting back from the carb, (classic weak mixture) etc. Your main jet will have to be an awful lot too big before its size will affect the mid-range of the needle adjustment.
The needle position should already be set by this time. In extreme cases, you may not have been able to get a rich enough needle setting, because the main jet may have been too small.
Variations in main jet size shouldn't affect needle setting, although if I've made big main jet changes, I always check the needle setting again.
The first 1/8 of throttle opening is affected by the pilot, or idle jet setting, and throttle cutaway affects the "transition" from idle circuit to needle. Adjust pilot jet at idle, alternating between the idle stop screw to get the lowest possible idle, and the pilot jet screw, to bring the idle up as much as you can. Throttle cutaway can only be changed by changing your slide, but fortunately, this is an adjustment that is seldom necessary. The indication that you need to will be hesitation (or worse) as you increase throttle from just above 1/8 to the needle range.
That's about all there is to getting your carb tuning "in the ballpark." Do remember that too lean a mixture will bring about overheating, often detonation and subsequent holing of the piston(s).
