I sent this to the other site but thought I'd run it out here too. Might help somebody with carb problems as there seems to be some confusion on how to clean the carb. If this doesn't belong here please feel free to delete.
Carburetor Cleaning Tips
Seems that there are differing ideas as to what carburetor servicing/cleaning should include. I see many internet posts, “I’ve rebuilt..." or “I’ve cleaned… this carb 5 times… and it STILL doesn’t work!” On all small engines such as cycles, lawnmowers, garden tractors, chainsaws etc. there are some basics that need to be attended to 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’ limits, meaning it’s cumulative in your system, Benzene being one of those. Bad stuff, wear rubber gloves [dishwashing gloves hold up well and are cheap] and allow yourself lots of fresh air!
A buddy was scrubbing carb parts in the wash basin in his garage, busy-busy and humming happily as he scrubbed away. Towards the end he wanted to wash up the parts and himself in nice hot water. He was bent over the double wash sink when he flipped on the hot water faucet handle, and this caused a chain reaction: the gas hot water heater a couple of feet away kicked on, igniting the accumulated gasoline vapors, also flashing across to the parts scrub pan filled with gas, the one in front of his face. He healed fairly well except for the scar tissues, but we still call him ‘Old Baldy’ or 'Squinty'.
Another potential problem is the highly toxic carb spray cleaner. Because the little red wand thingy doesn’t tightly seal to what you’re spraying the back splash can go right in the face & eyes, extremely not-fun. Goggles are strongly recommended, you only have one pair of eyes.
It’s good to soak the whole carb assembly either in gas, gas/oil mix, or gas & Yamaha Carburetor Cleaner before starting deep cleaning. This loosens up all the hard deposits. The assumption is you’ve got a carb gasket kit. Otherwise if you don’t then monitor the condition of rubber etc. while soaking.
Wearing your rubber gloves, dis-assemble the carb, making drawings or taking photos of parts relationships. Many carbs have online diagrams available but you may have to print them out and draw your own connecting lines to show exactly where parts fit together. I use an old cake pan to hold all the bits & pieces in one place. Complicated carbs might call for some baggies or something to hold parts groups together in one place.
Wearing your 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 assemblies are fairly clean it’s time to break out the spray can of carburetor cleaner. I prefer Berryman’s, a very high quality product that’s quite aggressive. Again some scrubbing is usually called for. Toothbrushes vary in quality, never noticed which brand lasts longer. Some are good for months, some wither away ¼ of the way through the job.
After this you’re getting into the nitty-gritty. There are several air bleeds in the throat of the carb, usually one near center and 2 or 3 in the inlet/filter area of carb throat. Sometimes these are in a boss and pressed or screwed in, others are simply a pin-hole bored into castings. I soak the carb in carb cleaner when possible, then use carb spray cleaner and a small wire, like a piece of guitar string [G, B or E string] or similar. The wire is used to gently swab out those tiny air bleeds, and to clean the jets.
Speaking of jets, inspect them closely and jot down any numbers for future reference and also to see how the carb is jetted now. When removing any adjustment needle screws write down the number of turns to remove so you can be ballpark close on reassembly.
When using a thin piece of wire like guitar string to clean out the tiny air bleed holes in carb throat you don't want to ream them out. Run the end of the wire across a sharpening stone or some emery paper to remove any burrs or really sharp edges before using. Also helps to cut the tip sharply on carb cleaner spray tube at a 45 degree angle so you can hold it tight against carb throat/venturi, over those tiny air bleeds, and direct the force as you wash them out.
In addition if you have several sizes of fine steel wire you can use the 'Go - No go' method, of inserting progressively larger diameter wires into orifice until you find the largest that fits. This may reveal just how clogged up things really are.
Both the aluminum body and the brass jets are much harder than many think so a gentle cleaning with the wire & carb solvent only removes shellac buildup, without increasing orifice size. Even then it can take some work to get shellac out. I find that the solvents evaporate very quickly so I try to use a minimum amount, but squirting repeatedly as I go along and once I’ve progressed in cleaning then start using heavier amounts to flush orifices etc.
Most bike & many small engine carbs have a brass emulsion tube that needs to be screwed out of lower carb body. This tube may have a jet screwed into one end, and may have very tiny little holes running crosswise. I mean hardly more than the diameter of a hair! I’ve come across several where gunk & shellac have these tiny holes completely hidden without a very close examination. I take a wad of fine steel wool or a small toothbrush-style wire brush and gently polish the outside of emulsion tube to reveal those hidden orifices.
Wires and carb spray cleaner working together remove the hardened fuel residues, with solvent sprayed though all orifices afterwards. Then, if available, finish this by hitting it hard [with your goggles on] with high pressure compressed air while cleaner is still wet. Carb will be good as new, far better than just a soak or a spray & wash job. You may have to carry your can of spray cleaner up to the local service station to spray carb and use their air, if you can find a genuine service station anymore.
Those air bleeds in combination with metering jets control fuel mixture when you crack the throttle, with the vacuum causing fuel to flow at proper rate at proper time. Blocked ‘air bleed’ orifices can mean too much air through carburetor throat venturi, causing a lean fuel condition and bog 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 that are apparent only at certain rpm's.
Sometimes a too-high float level can do the opposite, causing carb to dump fuel and bog. A clogged air filter or restricted intake will result in a too rich condition as well. Clogged jets can effect fuel flow & carb operation 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 also get a backfire through carb, not exhaust, that indicates an intake leak somewhere between carb mounting base and cylinder head. Spraying some carb cleaner or WD40 around that area with engine running will reveal intake leaks, as engine will speed up when you spray across area of leak. What works even better with no mess or residues is to use a propane torch with gas turned on at low setting, with TORCH NOT LIT, and playing un-lit propane gas around gasket & intake surfaces. Again, engine will speed up if there's a leak. Obviously there are some serious safety precautions necessary when using the propane torch so you don't ignite yourself or your investments.
If the machine runs okay or better with the choke partially or fully closed this of course indicates you’re too lean somewhere, either in adjustment or in clogged fuel metering jets and orifices or whatever.
On some small engines, motorcycles, ATC’s and ATV’s etc. the carburetor may have a ‘slide’ with a fuel metering pin/rod at the bottom, which pin rides up & down in main fuel inlet jet hole. The little circlip or ‘E clip’ locking clip can usually be removed to adjust this metering rod up & down, to adjust basic fuel metering. Unscrew the cap where throttle cable enters carb and gently lift out throttle slide to see this. Slide only goes in one way so a groove in slide & corresponding lugs in casting must be carefully [gently] re-aligned before reassembly. This slide should slip right out and if it doesn't then soak the carb longer and possibly use some pentrant. Moving pin upwards is usually richer, leaving jet more open, downwards leaner on fuel delivery as it more fully restricts opening.
A check of all fuel lines, clamps, vent lines, tank's gas cap gasket & vent holes, and actual throttle slide & twist grip cable components is easiest when you have it all apart. If you don't currently have an inline fuel filter this is a good time to install one! There are some automotive chassis greases that are surprisingly lightweight in viscosity and when used with a pin injector in a grease gun they’re great for lubing up carb cables. I don’t have much satisfaction with the dry lubricants there, and oil just runs on through.
A free old timer millwright trick is to ‘ring out’ gaskets. To do this you have your intended gasket sealing surface and a piece of paper gasket material. Using a small tack hammer and very light taps you can leave a clear impression in gasket material, telling you exactly where to cut it for a new home-made gasket! Other applications you may want to use different types of pressure instead of the hammer, especially with aluminum castings, like rolling or running a shaft, blunt object or whatever in the areas to leave the impressions. Then cut out with an X-acto knife or your razor-sharp Schrade Old Timer along impression lines and you’re good to go. Also there are sets of special hollow punches available for punching out perfect holes, these vary from tiny to 6” and larger.
When reassembling try not to over-torque any carb mounting gaskets because it’s a one-way street: after crushed to a certain thickness there’s no going back, so leaks become permanent. Just a few inch-pounds are all it should take in most circumstances.