Original Posting Date: 12-27-01
Topic: Basic Carburetor Rebuilding Information.
Intent: Basic Information for the first time Do-It-Yourself Person.
Contents: Carburetors used on both 2 and 4 Cycle Gasoline Small Engines. Helpful Suggestions, Tips, VIP Info and Cautions.
Some engine starting or operating conditions and problems may appear to be carburetor related. Always check for fuel flow out of the fuel tank, prior to any suspected fuel related engine problems and prior to removing any carburetor.
Basically, there are 2 types of carburetors used on small engined power equipment. The bowl type and the diaphragm type. Diaphragm carburetors are easy to identify because they do not have fuel bowls.
Diaphragm carburetors are mostly used on 2 cycle engines. Some 4 cycle engines may have a diaphragm carburetor while other 4 cycle engines may have bowl type carburetor.
Prior to removing any carburetor, be sure to make note of exactly how the throttle linkage is connected to the carb and the governor linkage is installed on either end. It's important to reinstall all parts exactly as they where originally installed.
TIP:
Use care handling any springs attached to the carburetors linkage. Be very careful not to overly expand any throttle or governor springs and equally as important not to bend any linkage rods.
Most carburetors have either 1 or 2 fuel adjustment screws. Should there be 2 fuel adjustment screws on either type of carb, one should be marked "H" for the high speed adjustment screw and another marked "L" for the low speed adjustment screw.
IMPORTANT INFO:
Prior to any carburetor disassembly, be sure to make note of exactly how many turns OUT WARDS each fuel adjustment screw is currently set at.
To determine how many turns each fuel adjustment screw is turned out wards, count the number of turns it takes to screw it IN WARDS, until the adjustment screw is lightly seated.
The number of turns in wards it takes to lightly seat the screw, will then be the number of turns out wards it takes to set the screw back to it's originally opened position, after the carburetor rebuilding process is completed.
DURING DISASSEMBLY:
Carefully remove each part of the carburetor and take special note of exactly how each part came off or in the case of part assemblies, exactly how the assembly came apart.
Take special note in which order each part or assembly came off and or came apart. Note which side or which direction each part currently is facing or installed, prior to removal and or disassembly.
IMPORTANT TIPS:
It is highly recommend to only disassemble carburetors on a well lighted, clean and completely cleared off work bench. Carburetor parts are usually tiny, often freely fall out of removed parts or assemblies and can become easily lost.
Using scribe marks on metal parts or assemblies of parts will help to replace the parts in the location each part was installed prior to disassembly.
DIAPHRAGM CARBURETOR NOTE:
On diaphragm carburetors, look for a small hole in the carburetors engine facing side. This hole is bored into the body of the carb around the mounting surface.
On the engine mounting surface is another hole which goes down into the engines crankcase.This hole provides both vacuum and pressure, which must be allowed to enter into the carburetor.
Both holes provide a path for engine crack case vacuum and pressure to act upon the diaphragm, causing it to fluctuate. The diaphragms fluctuations allows fuel to flow into the carburetor. Be sure both holes are cleared.
TIPS:
During the carb cleaning process, use canned aerosol automotive carb spray cleaner. Use it to clean the carb body, fuel ports, jets and airway passages.
The plastic extension tube, that comes with the canned cleaner, is an excellent tool to flush out sludge and debris from the jets, ports, fuel channels, airway passages, under Welsh plugs without removing the plug caps.
CAUTIONARY NOTE:
Use EXTREME CAUTION with canned aerosol automotive parts cleaner products. Aerosol cleaners are EXTREMELY FLAMMABLE!
Read the manufacturers product warning label.
SPECIAL NOTES REGARDING 2 CYCLE ENGINES:
Check for a fuel filter inside the bottom of the fuel tank or installed in-line with the fuel hose. Some two cycle engines may have a weighted fuel filter attached to the fuel hose end inside the fuel tank.
The filter and weight combo should be able to freely move around inside the tank. The purpose of the weighted filter is to allow fuel to be drawn up when the engine is operating at angles.
MUFFLER & FUEL TIPS:
Mufflers on two cycle engines are susceptible to becoming restricted or clogged up with carbon deposits. Should this happen, engine performance will be diminished. If this happens, the muffler will need to be removed, cleaned out and or replaced.
Care should be taken removing any muffler. Breaking off the head of a bolt or damaging the heads of a screw are possible. Be sure to reinstall the muffler and or spark arrester as currently installed.
The best preventative measure to help reduce carbon build up in the combustion chamber, exhaust system and muffler, is to use an ash less two cycle oil or the oil type specifically recommended by the manufacturer. Bare in mind that an overly rich oil to fuel mixture is not beneficial. Too much oil will do more harm then good.
Do not premix any more fuel and 2 cycle oil mixture then can be used in a month. Premix the correct amount of oil to fuel ratio into the fuel in a separate fuel container and store the container in a safe location.
Suggestions:
Read the equipments owners manual. Check the manufacturers product online web site and purchase a repair manual specific to the engine and equipment, if possible. Helpful repair aids provide useful information, problem solving methods, disassembly, reassembly repair procedures, instructions, pictorials and schematics.
An excellent source for original replacement parts, generic service and repair manuals, is your local retail lawn mower and or small engine repair shops. Small engine powered equipment dealers and repair shops are listed in the phone book.
Most retail dealers can help determine what a possible engines problem may be, prior to attempting a carb overhaul. Be sure to take the engines brand name, model and serial numbers with you, if you stop in at the store.
HINTS:
When dealing with shop owners and or their mechanics, it's recommend to "ASK QUESTIONS." Not all repair shops operate the same nor include the same services for the terms and or phrases commonly used. Know the differences.
Question Examples:
Does the engine need a "Minor Tune-Up or a Major Tune-up?" The two are not the same. Ask what each service includes.
Does the engine only need a "Carburetor Adjustment" or a complete "Carburetor Overhaul?" Ask what each service includes. Not all shops operate in the same manner.
TUNE-UP NOTE:
A Minor Tune-up often includes only carburetor adjustments, when needed, with ignition services. A Major Tune-up may or may not include a carburetors complete rebuilding.
Regards & Good Luck. Sharp Advice.
Master Small Engine Tech. Web Site Host, Forums Monitor and Multiple Topics Moderator. "Accurate Power Equipment Company." Small Engine Diagnostics Services & Repair.
Fast...Fair...Friendly & Highly Proficient Services....
UPDATED VERSION.
POSTED 04-16-04
Basic Carburetor Rebuilding Information.
Topic: Basic Carburetor Rebuilding Information.
Intent: Basic Information for the first time Do-It-Yourself Person.
Contents: Carburetors used on both 2 and 4 Cycle Gasoline Small Engines. Helpful Suggestions, Tips, VIP Info and Cautions.
Some engine hard starting, running or operating conditions and problems may appear to be carburetor related. Such may not always be the case. Many possible conditions can cause some problems to appear to be carburetor related conditions but not really be so.
Always check for fuel flow out of the fuel tank, when a carb problem is suspected prior to any suspected fuel related engine problems and always prior to removing any carburetor.
Basically, there are 2 types of carburetors used on small engined power equipment. Diaphragm carbs and bowl carburetors. Diaphragm carburetors are usually easy to spot because they do not have fuel bowls.
Diaphragm carburetors are mostly used on 2 cycle engines. Also
used on power equipment which may need to be turned at angles or not used while in a non level position. 2 such examples would be chainsaws and string trimmers.
Some 4 cycle engines may have a diaphragm carburetor while other 4 cycle engines may have bowl type carburetor. There is no assurance which type of carb is used on mowers and edges, etc.
Once all other possibilities are assured not to exist on the power equipment, only than should the carb be suspected and or removed for service and or repairs.
Prior to removing any carburetor, be sure to make note of exactly how the throttle linkage is connected to the carb and the governor linkage, if equipped, is installed on either end of the linkage. It's important to reinstall all parts exactly as they where originally installed.
TIP:
Use care handling any springs attached to the carburetors linkage. Be very careful not to overly expand any throttle or governor springs and equally as important not to bend any linkage rods.
Most carburetors have either 1 or 2 fuel adjustment screws. Should there be 2 fuel adjustment screws on either type of carb, one should be marked "H" for the high speed adjustment screw and another marked "L" for the low speed adjustment screw.
IMPORTANT INFO:
Prior to any carburetor disassembly, be sure to make note of exactly how many turns OUT WARDS each fuel adjustment screw is currently set at.
To determine how many turns each fuel adjustment screw is turned out wards, count the number of turns it takes to screw it IN WARDS, until the adjustment screw is lightly seated.
The number of turns in wards it takes to lightly seat the screw, will then be the number of turns out wards it takes to set the screw back to it's originally opened position, after the carburetor rebuilding process is completed. Write the number of turns down on paper.
DURING DISASSEMBLY:
Carefully remove each part of the carburetor and take special note of exactly how each part came off or in the case of part assemblies, exactly how the assembly came apart.
Take special note in which order each part or assembly came off and or came apart. Note which side or which direction each part currently is facing or installed, prior to removal and or disassembly.
IMPORTANT TIPS:
It is highly recommend to only disassemble carburetors on a well lighted, clean and completely cleared off work bench. Carburetor parts are usually tiny, often freely fall out of removed parts or assemblies and can become easily lost.
Using scribe marks on metal parts or assemblies of parts will help to replace the parts in the location each part was installed prior to disassembly.
DIAPHRAGM CARBURETOR NOTE:
On diaphragm carburetors, look for a small hole in the body of the carburetors engine facing side. This hole is bored into the body of the carb around the mounting surface.
On the engine mounting surface is another hole which goes down into the engines crankcase.This hole provides both vacuum and pressure, which must be allowed to enter into the carburetor.
Both holes provide a path for engine crack case vacuum and pressure to act upon the diaphragm, causing it to fluctuate. The diaphragms fluctuations allows fuel to flow into the carburetor. Be sure both holes are cleared.
TIPS:
During the carb cleaning process, use canned aerosol automotive carb spray cleaner. Use it to clean the carb body, fuel ports, jets and airway passages.
The plastic extension tube, that comes with the canned cleaner, is an excellent tool to flush out sludge and debris from the jets, ports, fuel channels, airway passages, under Welsh plugs without removing the plug caps.
This process and procedure above usually works but not always. The intent is to avoid removal of some parts and or carb pieces which are pressed in and or may be more difficult to replace.
CAUTIONARY NOTE:
Use EXTREME CAUTION with canned aerosol automotive parts cleaner products. Aerosol cleaners are EXTREMELY FLAMMABLE!
Read the manufacturers product warning label.
SPECIAL NOTES REGARDING 2 CYCLE ENGINES:
Check for a fuel filter inside the bottom of the fuel tank or installed in-line with the fuel hose. Some two cycle engines may have a weighted fuel filter attached to the fuel hose end inside the fuel tank.
The filter and weight combo should be able to freely move around inside the tank. The purpose of the weighted filter is to allow fuel to be drawn up when the engine is operating at angles.
MUFFLER & FUEL TIPS:
Mufflers on two cycle engines are susceptible to becoming restricted or clogged up with carbon deposits. Should this happen, engine performance will be diminished. Difficulties with engine running and hard starting are symptoms.
If muffler restriction is suspected, the muffler will need to be removed, cleaned out and or replaced. Care should be taken removing any muffler. Breaking off the head of a bolt, damaging the heads of a screw or the threads, etc are possible. Be sure to reinstall the muffler and or spark arrester as currently installed.
The best preventative measure to help reduce carbon build up in the combustion chamber, exhaust system and muffler, is to use an ash less two cycle oil or the oil type specifically recommended by the manufacturer in the ratios recommended. Bare in mind that an overly rich oil to fuel mixture is not beneficial. Too much oil can do more harm then good.
Do not premix any more fuel 2 cycle oil mixture then can be used in a month. Premix the correct amount of oil to fuel ratio into the fuel in an approved, separate fuel container and store the container in a safe location.
Suggestions:
Read the equipments owners manual. Check the manufacturers product online web site and purchase a repair manual specific to the engine and equipment, if possible. Helpful repair aids provide useful information, problem solving methods, disassembly, reassembly repair procedures, instructions, pictorials and schematics.
An excellent source for original replacement parts, generic service and repair manuals, is your local retail lawn mower and or small engine repair shops. Small engine powered equipment dealers and repair shops are listed in the phone book.
Most retail dealers can help determine what a possible engines problem(s) may be, prior to attempting a carb overhaul. Be sure to take the engines brand name, model and serial numbers with you, if you stop in at the store.
HINTS:
When dealing with shop owners and or their mechanics, it's recommend to "ASK QUESTIONS." Not all repair shops operate the same nor include the same services for the terms and or phrases commonly used. Know the differences.
Question Examples:
Does the engine need a "Minor Tune-Up or a Major Tune-up?" The two services are are not exactly the same. Ask what each service includes.
Does the engine only need a "Carburetor Adjustment" or a complete "Carburetor Overhaul?" Ask what each service includes. Not all shops operate in the same manner.
TUNE-UP NOTE:
A Minor Tune-up often includes only carburetor adjustments, when needed, with ignition services. A Major Tune-up may or may not include a carburetors complete rebuilding.
Regards & Good Luck. Sharp Advice.
Master Small Engine Tech. Web Site Host, Forums Monitor, Manager and Multiple Topics Moderator. "Accurate Power Equipment Company." Small Engine Diagnostics Services & Repair.
Fast...Fair...Friendly & Highly Proficient Services....