I would disregard what seller said about having just cleaned carbs. Reason is it can be a crock outright, or else he may know nothing about proper carb cleaning. It may mean he hosed off the outsides with carb cleaner: 'There, I cleaned the carbs!'
Unless you're absolutely sure the carbs have been properly cleaned recently then it wouldn't be good to try to simply rejet with carbs in place. Also there's a chance for some screwups in trying to do it that way unless you're really familiar with working on the particular carb, in place.
Here's some info on carb theory:
http://roadstarclinic.com/content/view/56/96/Here's some lengthy info on Carburetor Cleaning:
Carburetor Cleaning Tips
Much words here but it seems there’s differing ideas as to what carburetor servicing or cleaning should include. I’ve seen countless internet posts, “I’ve rebuilt/cleaned this carb 5 times and it STILL doesn’t work!” On all small engines such as motorcycles, mowers, garden tractors, chainsaws etc. there’s some basics that need to be addressed in order to ‘Get it right the first time'.
First off: don’t get too cavalier with gasoline! It’s highly dangerous and toxic and several components have ‘Allowable Lifetime Dosage Limit’ meaning it’s cumulative in your system - Bad stuff, wear rubber gloves [Dishwashing gloves hold up well and are cheap] - allow yourself lots of FRESH AIR! A buddy was cleaning parts in his sink in the garage, busy-busy as he scrubbed away. Towards the end he wanted to wash up parts and hands in nice hot soapy water. Bent over the concrete double wash sink he flipped on the hot water faucet handle, causing a swift chain reaction. Hot water drawn off caused gas water heater burner to kick on a few feet away, igniting gas vapors in garage and flashing across to sink vapors and parts scrub pan filled with gas: THE ONE RIGHT IN FRONT OF HIS FACE! They rebuilt that part of garage while he healed fairly well except for the scar tissues. We still call him ‘Old Baldy’. NO SMOKING AREA!
Another potential problem is TOXIC carb spray cleaner vapors! Also the little red wand thingy doesn’t want to seal tight to what you’re spraying so the back splash can go right in the face and eyes, extremely not-fun. Goggles are strongly recommended, you only have one pair of eyes!
Some carb rubber parts are destroyed by carburetor spray cleaners so it’s best to clean carb with gasoline, GENTLY disassemble and remove rubber parts before proceeding farther. It’s good to soak the whole carb assembly either in a coffee can or smaller can of gas, gas/oil mix, or gas & Yamaha Carburetor Cleaner before starting deep cleaning. Coffee cans are nice because of soft plastic lid to prevent accidental spillage or ignition. The assumption is you’ve got a carb gasket kit. Lots of carbs that you don’t need a kit at all, just careful disassembly, cleaning and reassembly. Otherwise if you don’t then monitor condition of rubber etc. while soaking but gas alone won’t hurt things.
Disassemble carb, making drawings or taking photos of parts relationships. Many carbs have online diagrams available. Best to print them out to scribble notes and draw your own little connecting lines to show exactly where parts fit together. I use old cake pans and cup cake or muffin tins to hold all the small bits & pieces. Complicated carbs or racks might call for some Zip-Lock baggies or something to hold parts groups together in one place. TIP: mark Zip-Locks with a Sharpie for extra safety in case rebuild gets delayed, oh wooops!
Remove air/fuel adjustment/mixture screws by first turning them in, counting number of turns till JUST SEATED - NOT SEATED HARD! Write that number down on your guide sheet, remove screw, on to the next. Wearing rubber gloves, using an old toothbrush and some gasoline scrubs off most of the outside of carb, unless you soaked in Yamaha Carburetor Cleaner which already did that for you! After it’s fairly clean, time to break out the spray can of Berrymans Carburetor Cleaner. I prefer Berryman’s, a very high quality product that’s quite aggressive. Cut the tip of spray tube at 45 degree angle to hold it tight against carb throat/venturi and over tiny air bleeds to direct the force as you wash them out. One straight and one 45* are handy to have and you’ll probably use up 2 can of Berrymans anyway.
There’s several air bleeds and holes in carb throat, usually one near center and 2 or 3 at inlet/filter area of carb throat on or inside the rim. Sometimes these are in a boss and pressed or screwed in, others are a simple pin-hole bored into castings. Cycle carbs have the Needle Jet screwed into center of throat below slide piston too. I soak the carb body in carb cleaner then use carb spray cleaner and small wires, like pieces of guitar string, G, B or high E string or similar wires depending on orifice size. The wire is used to gently swab out tiny air bleeds and clean jets. DON’T USE COPPER OR BRASS WIRE! Bending back & forth anneals and softens it so it quickly wants to break off right at edge of hole: now you’re screwed! Special sets of Carburetor Jet Cleaning Wires are available online, much like acetylene torch tip cleaners.
http://www.z1enterprises.com/Carburetor-Cleaner-wire-set-236.aspxhttp://jet200.com/catalog/product_info.php?cPath=8&products_id=135 When using a thin piece of wire like guitar string to clean out tiny air bleeds and jets you don't want to ream them out. Run the cut end of wire across a sharpening stone/emery paper or fine file to remove burrs or really sharp edges before using!
In addition if you have several sizes of fine steel wires you can use the 'Go - No go' test method. Start small and gently insert progressively larger diameter wires into orifice as you clean until you find the largest that easily fits. This reveals just how clogged up things really are. Insert a small one with carb wet, wiggle it around a bit to break caked deposits, spray it some, try a bigger wire. You’re not out to resize the hole, just to break up deposits! Hard force is rarely needed! Take your time, carbs are expensive.
Both the aluminum body and brass jets are much harder than many think so gentle cleaning with wires and carb solvent only removes shellac and built up deposits without reaming or increasing orifice size. Even then it can take some work to get shellac out. I find that solvents evaporate quickly so I try to use minimum amounts, squirting repeatedly as I go along. Once I’ve progressed in cleaning then start using heavier amounts to blast orifices.
Inspect Jets closely and jot down any numbers for future reference, also seeing how carb is jetted now. On a rack of carbs if numbers aren’t visible use your wires as Go/No-Go gauges to make sure all Jets match. Again, when removing any adjustment needle screws write down the number of turns to remove so you’re ballpark close on reassembly. In float bowls a hard wooden or plastic stick with one end pointed, other end like a flat screwdriver helps clean bowl irregularities.
Most bike and small engine carbs have a brass Emulsion Tube that needs to be screwed out of lower carb body. This Emulsion Tube may/should have a Jet screwed into one end and has very tiny little holes running crosswise. I’ve come across several where gunk & shellac have these tiny holes completely hidden without a very close examination. A wad of fine bronze/brass wool, small toothbrush-style brass brush or Scotchbrite pad gently cleans and polishes Emulsion Tube to reveal those hidden holes. All Emulsion tubes I’ve ever seen have a hole at the far end/domed end opposite Jet in addition to crosswise holes in the sides. Makes very sure that’s open too.
Wires and carb spray cleaner working together remove hardened fuel deposits with solvent sprayed though all orifices afterwards. If available finish by hitting with compressed air while spray cleaner’s still wet, not mandatory but sometimes helps. Carb will be good as new, far better than just a soak or ‘Spray & wash’ job.
Air bleeds in combination with metering jets control fuel/air mixture when you crack throttle, with vacuum causing fuel to flow through Jets at proper rate at proper time. Blocked air bleed orifices can mean too much air through carb throat venturi while not drawing enough fuel, causing a Lean fuel condition and stumbling because weak vacuum signal isn’t pulling fuel in. In many cases one or two are more clogged than others, causing horrible imbalance in metering circuits and problems only apparent at certain rpm's.
Sometimes a too-high float level or Needle Jet Needle can do the opposite, causing carb to dump fuel and bog Rich. A clogged air filter or restricted intake will result in too rich condition too. Clogged Jets effect fuel flow throughout any operating ranges. Too lean and you may be buying new valves soon, after you pound the seized piston out of the scored cylinder bore.
If you get backfires through carb, not through exhaust, that indicates intake leaks somewhere between carb mounting base and cylinder head. Spray carb cleaner or WD40 around carb base and intake manifold areas [not air filter intake] with engine running to reveal leaks, as engine speeds up when you spray across leak. Even better, use a Propane Torch with gas turned on low setting, with TORCH NOT LIT, playing UN-LIT propane around head-to-manifold and carb gasket surfaces. Engine speeds up if there's a leak. Obviously serious safety precautions necessary with Propane Gas!
If machine runs okay or better with choke partially or fully closed this indicates you’re lean. Could be adjustment, clogged fuel metering jets, air bleed orifices or the Needle Jet Needle set too low.
On some small engines, motorcycles, ATC/ATV the carburetor has a ‘slide’ with a Fuel Metering Needle/Rod at bottom, which Needle rides up & down in Main Needle Jet/Fuel Inlet Jet hole. The little circlip or ‘E clip’ locking clip on needle can be moved to adjust. Unscrew cap where throttle cable enters carb body and gently lift out throttle slide. Slide only goes in one way so a groove in slide & corresponding lugs in body casting must be carefully aligned! NEVER FORCE IT IN! It’s always a very light slip fit! This slide should slip right out and if it doesn't then soak carb longer and possibly use some WD40. Moving E clip UP moves Main Jet needle Down, causing more Lean condition. Moving E clip DOWN moves Jet Needle UP causing Rich metering. This is your basic off-idle Fuel Metering as Jet Needle moves to open or restrict Main Needle Jet fuel flow.
Small engines usually have 3 steps in air/fuel control: Idle Circuit, High Speed/Main Jet Circuit and WOT. The Idle Circuit is controlled by Idle Jet size and air bleed orifices and air adjustment or idle screw. Main Circuit is controlled by Slide Piston and Main Needle Jet, or by throttle butterfly and Main Jet. WOT Circuit is by air bleeds, Main Jet and Fuel Metering Jets with slide or butterfly Wide Open Throttle. Stumbling when coming off idle says the transition to Main is too Lean, where a bog says too Rich from what I’ve seen.
A check of all fuel lines, clamps, vent lines, gas cap gasket and cap vent holes, throttle slide and twist grip cable components is easiest when it’s all apart. If you don't currently have an inline fuel filter/s it’s a good time to install. Some automotive chassis grease is lightweight viscosity and used with a pin injector in grease gun it’s great for lubing up cables.
To ‘ring out’ gaskets: lay gasket material on part to be sealed. Use a small hammer and very light taps to leave clear impression in gasket telling you where to cut it for a nice home-made gasket! Other applications you may want to use different types of pressure instead of a hammer, especially with zinc or aluminum castings, like rolling or running a shaft, blunt object or whatever in the areas to leave impressions. You can buy special round hollow sharpened punches for punching out perfect holes, or take a piece of tubing and file and sharpen one end at an angle about 45*. When reassembling try not to over-torque any carb mounting gaskets. After being crushed to a thickness there’s no going back: if it leaks it’s permanent. Just a few inch-pounds are all it should take in most circumstances.
For my part, anybody who needs to copy this is free to do so, just don't take credit for writing it, thanks!
XLerate
