Carb concerns

Scott Nesbitt

In an era when everyone is “going green,” it’s worth a review of how the service shop’s handling of carburetors affects both “green” environmental concerns and the “greenbacks” that your course spends on equipment.

Carburetors have almost disappeared from the world’s highways, replaced by computer-controlled fuel injection systems. But the carburetor remains the dominant way to mix fuel and air to feed the air-cooled engines found on string trimmers, chain saws and a lot of mowing and blowing equipment. With electronic ignition and improved engine designs, the carburetor and fuel system are about the only things that need the technician’s delicate touch for adjustment and proper servicing.

Since the new millennium started in 2000 (OK, we’ll have the 2000/2001 argument later), these carburetors have changed dramatically to produce leaner, cleaner exhaust from small engines. The increased precision has raised fuel efficiency, so you use less fuel per hour of operation. That’s a good thing. Yet it’s a cause for concern, because the high-precision carburetors leave a smaller margin for technician error in adjustment and servicing. Using the wrong parts or tinkering with the needles can quickly destroy an engine.

Here are some thoughts on avoiding problems:

When buying new air-cooled equipment, have the dealer look up the exact make and model number of the carburetor. Buy a complete carburetor service kit and a few fuel filters for the machine, and keep those parts in a file and clearly marked, so you know which parts go with which machine. Don’t assume that because you have three trimmers of the same model and maker that all will have exactly the same carburetor with the same characteristics.

Do not remove the adjustment needle limiters found on most new equipment. Unless you have all the technology and training available to the engineers at the factory, don’t pretend you can beat the system with good-old-boy fiddling.

Throw away old parts. Don’t try to reuse adjustment needles from old machines, or slap any old carb onto a machine just because it fits. 

Pay special attention to mounting gaskets and air filters. Bad gaskets leak air and cause lean running; dirty air filters throw off the air-fuel mixture and result in poor performance, wasted fuel and reduced machine life.

Invest in extra-good fuel filters and change them at least once a year. Proper fuel flow is critical to accurate metering inside the carburetor.

Finally, make sure you frequently clean the cooling fins and intake screens on the air-cooled engines to maintain an engine temperature range that’s correct for the carburetor and fuel system. You may waste a lot of time trying to solve a carburetor problem when the real cause of the trouble is overheating that throws off the delicate balance of air and fuel your engines need to run right.

Scott R. Nesbitt is a free-lance writer and former GCSAA staff member. He lives in Atlanta.