QuestionI have rebuilt this carburator and still cannot get it to prime correctly. I have cleaned out bowl retaining screw holes and installed orings onto plastic pick up tube and replaced inlet valve seat. I had to adjust engine speed high for carburetor to pick up and run takes a few minutes of surging before engine stabilizes
Answerjimmie
Cleaning Craftsman (Tecumseh) carburetors
Simple float carburetors are found on a variety of equipment including many engines made for Sears by Tecumseh. The basic procedures applies to the float carburetors of other manufacturers as well.
If you have been following the recommended preventive maintenance procedures, this may never be needed. But, face it, you do not! The most important PM that is not likely done by 90 percent of mower owners is to drain the gas at the end of the season. With float type carburetors in particular, the result is a buildup which eventually clogs the very fine passageways in the carburetor. What happens is that the gas in the carburetor bowl gradually evaporates leaving behind the gunk and varnish. New gas then flows in from the fuel tank which then evaporates leaving behind more gunk and varnish, and so on and so on and so on. This eventually, well, gums up the works by interfering with float movement and clogging the precision metering holes. Thus, the need for cleaning. Symptoms include difficulty in starting, flooding, surging, lack of power, difficulty in restarting when hot, etc.
The following procedures are specifically for the common non-adjustable carburetors used on the vast majority of Craftsman mowers manufactured in the last 10 years. Carburetors with adjustments and/or a choke are slightly more complex and may differ in other ways. Refer to a small engine repair book or your engine manual for further information.
Carburetor removal
Drain the fuel, close the shutoff valve if any, or remove the gas tank. On the common Craftsman mowers, the tank either slips off or is fastened with a couple of screws. The gas line should pull right off. Inspect the fuel line for damage or cracking and replace it if these are severe.
Remove the air filter, inspect, and set aside. The small plastic enclosed air filters twist off counterclockwise. If it is clogged and of the paper type, replacement will be needed. If it has a foam element, this can be reused if it doesn't fall apart. Remove the foam element, clean in soap or detergent and water, dry, and then coat it with a few drops of fresh engine oil. Work the foam with your fingers to distribute the oil. For other types, see your engine manual.
Use a large philips screwdriver to loosen the two screws fastening the intake manifold to the cylinder block. If the gasket separates easily and cleanly, then it can be reused though a dab of non-hardening sealer is advisable once you have tested the mower to be sure that your newly restored carburetor is functioning properly. If it tears or is damaged in any way, then it should be replaced.
If the bolts are really tight, an open end wrench may be of help but common sockets may not fit around the bottom bolt. Thin walled sockets may work.
Disconnect the throttle linkage and governor spring noting which holes they go in. IMPORTANT: If you get this screwed up you could have a runaway situation on your hands when you go to restart it. This can destroy the engine in a few seconds!
Disconnect the rubber tube from the primer bulb, if any. It should pull off. If it tears near the end, there is probably enough slack so that a new tube is not required.
Disconnect the speed control and stop switch wire, if any. Note how they are installed.
The carburetor can now be moved to the convenience of your workbench.
WARNING: there is still likely a significant amount of gas inside the float bowl. Initial disassembly at least should be done outside so that you can dispose of this safely. Working outside is advisable in any case as the common carburetor cleaning solvents are both flammable and bad for your health.
Disassembly
Most carburetors on Craftsman mowers are variations on a common float design. Newer mowers tend to have no adjustments and no choke - which greatly simplifies cleaning and adjustment. With respect to adjustment, there is none - it either works or it doesn't. If it doesn't, your cleaning was not thorough enough, some parts need replacement, or the problem is not in the carburetor.
IMPORTANT: Before removing any linkages or springs, make detailed diagrams as to how everything goes together. You will NOT remember this several hours later!!! Reassembling the linkages EXACTLY as your found them is critical to the happiness of your engine.
Under the bowl is a large hex head bolt. On the non-adjustable carburetor, this is closed on the bottom. It is also not a simple bolt but includes the precision main fuel metering hole which will need to be cleaned thoroughly. Use a proper socket to unscrew this bolt (counterclockwise). Drain any residual gas from the bowl. CAUTION: I've heard of people breaking the bolt by either attempting to loosen it the wrong way or overtightening upon reassembly to stop leaks.
There is a fiber washer under the bolt. There may also be a fiber washer on this nut inside the float bowl. Don't lose these or get them mixed up.
Turn the carburetor upside-down.
Carefully remove the bowl and O-ring. Inspect these for damage. (Note: there is probably a dimple in the bottom of the bowl in the lower level side. This is normal and probably there to keep the float off of the bottom where gunk and varnish collect because you didn't drain the gas.)
The float will now be visible. Rotate it to the fully up position. The inlet needle will come up with the hinged part of the float. It is held in place by a wire clip but will now be free. The inlet needle is actually a four sided metal rod with a polished conical tip. Remove the needle and clip.
Use a pair of needlenose pliers to pull out the hinge pin which will free the float. Careful - the float is made of relatively thin brass and is susceptible to damage.
Check the throttle plate for free movement - there should be absolutely no hint of binding or tightness. If there is, then this will need to be disassembled as well and cleaned:
Use an open-end wrench to loosen the intake pipe and then remove the nuts and bolts. The manifold will probably come free with the gasket intact. Don't lose the metal strip to which the governor spring attaches. Check for dirt and other debris and set aside.
Use a 1/8" straight blade screwdriver to remove the screw in the center of the throttle plate. Note the position of the hole in the plate and the orientation of the plate. (The hole should be toward the engine side with the carburetor body upright. Mark it before removal if in doubt.)
Tap the carburetor if needed to remove the throttle plate.
Pull the throttle shaft out of the carburetor body. Take care not to lose the spring with the felt and/or metal washer. Note their positions.
Cleaning the carburetor parts
Use carburetor cleaner and lint free cloths or paper towels to remove all built up brown or green gunk, varnish, and other contamination from the metallic parts. Pay particular attention to the machined passages and metering holes.
WARNING: Carburetor cleaner is both flammable and the fumes are toxic. Do all cleaning away from open flames and outdoors if possible. Wear eye protection. The stuff will also eat plastics including some plastic eyeglass lenses.
Take care where non-metallic parts are still in place as extended contact with harsh solvents may degrade their properties (inlet seat and primer bulb, if present). Low pressure compressed air may be used to blow out passages but only use this on the fuel line from inside the carburetor body - else you may end up with the inlet seat clear across the driveway never to be found again.
DO NOT use wires or metal instruments to clear any of the passages as their size is critical.
The small hole in the hollow bolt on the bottom is most critical. Make sure it is cleaned down to the shiny brass and that this hole is unblocked and fully open:
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| | _ Hole in nut (approximately .025") - use carburetor cleaner
| | | | and wooden toothpicks to clear it out down to shiny brass.
| | | | DO NOT use metal wires!
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If you are absolutely sure there is no hole in the bolt (some models may forgo this), check further up on the central tube - there may be a tiny hole about 1/2" from the bottom. There has to be a hole somewhere for the gas to be sucked up through the carb!
I first use carburetor cleaner inside and out with cotton swabs to remove all traces of gunk from the inside. Use as many as needed till no more discoloration shows up. Then, use the broken end of a wooden toothpick or popsicle stick to clear the .5 mm diameter hole in the side. In severe cases, this hole may not even be immediately visible due to the varnish and gunk buildup.
If this hole is narrowed or clogged, the engine may start but then die in a few seconds. Gas enters the reservoir in the nut slowly or is forced in by priming but the normal suction cannot replenish it quickly enough.
Fine steel wool may be used on the float hinge pin if it is rough or there is evidence of rust but do not use anything abrasive on any of the other parts. Persistence with carburetor cleaner and cloths or paper towels should prove sufficient.
Inspect the inlet needle and seat. The needle should have sharp uniform edges and no visible damage to the conical tip. Any damage half way down the conical part - where it actually contacts the seat - will result in leakage and flooding. The seat can be removed if damaged by pulling it out with a hooked wire - careful - you do not want to scratch the body! If removed, do not reuse but install a replacement. The new seat goes in groove side first (lubricate with a drop of oil) and can be pressed home with a blunt rod.
If the throttle plate was disassembled, clean these parts with carburetor cleaner. Use a cotton swab to get into the bearing surfaces in the carburetor body.
DO NOT attempt to disassemble the carburetor beyond this point - the pressed in main fuel nozzle is precisely fitted and is not removable. The welch plug (pressed in disk) should not be removed unless you suspect contamination in the primer chamber (if any).
Carburetor rebuild kits are available and are economical where almost any parts need replacement.
