Carburetors play a vital role in the performance of any combustion engine, so small engine owners should take the time to appreciate common carburetor problems and solutions before more expensive issues arise.
The role of a carburetor is to regulate the intake of fuel into an engine while simultaneously mixing it with the correct quantity of air for optimal engine performance. There are two main types of carburetors
Float Type - Used mainly on stationary engine, and typically located below the fuel source, as gravity is relied upon for fuel delivery. Standard lawn mowers typically feature this type of carburetor
Diaphram Type - Used more on most handheld equipment like chainsaws, brushcutters, hedge trimmers, blowers etc. This common kind of simple carburetor is generally mounted above the fuel tank and has no fuel bowl or float. Vacuum pressure is used to draw fuel into the assembly.
The best way to understand the operation of carburetors is to think of them primarily as air pumps. For instance , when you power up the throttle, you are not pumping more fuel into an engine - on the contrary, you are really ramping up the air intake into the system, which then increases the fuel inflow and dynamics accordingly. As such, a carburetor is essentially dependent on two dominant features to work properly. ie. a clean, uninterrupted air intake , plus a clean, uninterrupted liquid fuel intake. yes the word clean is there for a reason . If either the air or fuel intake mechanisms are dirty or impaired, a number of problems may become apparent . The engine :
- Wont start at all
- Takes a large number of attempts to start
- Surges, even at idle
- Performs differently at high or low revs
- Leaks fuel
- Cuts out at idle
When it comes to substandard cleanliness, one of the most obvious culprits is dirty fuel. This happens frequently in cases where an owner leaves a fuel tank full and then doesn’t use the equipment for an extended period of time. In southern states, in particular, this can occur if equipment is used seasonally. There are some cool climates where lawn mowing, for example, comes to a standstill over winter when turf is near dormant, only for activity to resume sharply in mid spring. A chainsaw, similarly, might be used primarily in summer or autumn to allow wood to dry out in time for winter use. In these kinds of cases, fuel can become stale, even worse, the internal parts of the carburetor , including the delicate fuel inlet jet or fuel lines, can become gummed up.
Even if the fuel supply and delivery systems are in peak condition, there are other elements of the carburetor that might be dirty or out of balance, which can lead to sub-optimal performance. The best place to start is to watch and listen to the engine and identify telltale signs that something is out out of kilter. A good place to start is the spark plug, which can reveal a lot about how an engine is operating. If the spark plug end is a coffee colour, then its running fine, a ghostly white means its running lean or sooty black means its running to rich.
The term running lean means less than normal fuel supply is reaching the engine, whereas running rich implies excess fuel is being fed into the system . These levels can be adjusted manually with the mixture adjustment screw, of course but first it pays to ensure all other parts of the carburetor are in good order. It is always advisable to check all basic mechanical systems thoroughly before starting to manipulate factory settings. An added danger is that emissions compliant machinery can easily become non compliant if an owner inadvertently runs a rich mixture. So before tinkering with settings, make sure all parts are clean, undamaged and assembled to correct tolerances.
The obvious first step with cleaning a float carburetor is to unscrew the bowl and give it a good wash and soak using a dedicated carburetor cleaning fluid. Don’t be afraid to leave parts soaking overnight for a really penetrative clean, mindful that less durable plastic bits are like the float itself should not be subjected to prolonged corrosive exposure. Once clean, the float should be able to move up and down unhindered, so be sure to remove every skerick of gunk. Delicate jetter needles, which can easily become blocked, may need extra attention. A good yip is to avoid using old cloths that can leave behind unwanted lint, dust or fabric contaminates. It is far preferable to rinse with water and then use compressed air to blast away any cleaning agent residue and gunk, leaving behind a pristine surface before reassembly. This method works for sand filled fishing reels, and it works for engine parts too. If you aim to carry out your own carburetor maintenance routinely, it is worth investing in a basic toolkit to help maximize the effectiveness of your work.
While a solid cleanout will solve 90% of problems associated with a poor performing carburetor, there is always the chance thats a mechanical fault is to blame for a chronic problem. As mentioned carburetors are essentially pumps, which means leaky seals, split rings and damaged gaskets may need to replaced. Choke and throttle plates may also be bent or damaged due to wear and tear, stress or impact, or they may be in need of screw adjustments.
Taking good care of your carburetor is worth the effort , ignoring a problem can lead to poor fuel efficiency , premature engine were or worse. Carburetor maintenance therefore is crucial to maintaining a smooth running engine.