One of the most common jobs here at the shop is cleaning carburetors. Right around the first 65°, sunny day each Spring call after call has the same theme:
“My bike won’t start even though I just put a brand new battery in it.”
“My bike will run but it’s leaking gas.”
“My bike is backfiring really bad.”
“My bike runs fine until I turn the choke off.”
“My bike doesn’t seem to have the same power as when I parked it last Fall.”
It’s also the most common job for us to get in that needs “redone” after other shops or individuals have attempted the repair. In fact, it’s extremely common for us to diagnose the symptoms as needing a carb clean only to have the customer pipe back with, “But I just had the carbs cleaned somewhere else!”.
While it’s not a particularly technical skill, experience and knowledge is necessary. Today we’ll break down the ins and outs of carburetor cleanings.
Why do carbs need cleaned?
There are a few different scenarios that might commonly lead to carburetors needing cleaned:
The most common culprit is stale, old fuel. The fuel we use today is unleaded, which does not have the same storage stability as leaded fuel. This is especially true in small volumes, such as what is held within the float bowl of a carburetor- maybe 1/4 of a cup. This leads to what we often refer to as “gummy carbs”: the thick, slimy substance with a pungent odor that remains after all of the good qualities evaporate, often after sitting for an extended period of time. That sticky, stinky substance is what clogs the tiny passageways inside of the carburetor.
Remedy: Drain carburetors prior to storage and/or include a fuel stabilizing additive to your long-term storage routine.
Even with fresh fuel and frequent use of the machine, the carbs can still become blocked or dirty due to rust or debris inside of the fuel tank traveling down into the carburetor. Debris is more commonly found in off-road applications and is believed to be caused from refueling in extreme conditions (mud, snow, dust, etc.).
Remedy: Rust is usually due to the age of the motorcycle and can often be prevented by storing with the tank full of fuel. This is because what is under gas will not rust and therefore offers a simple, effective solution. Dirt and debris can be better prevented from entering the fuel tank by removing gloves/cleaning hands and using a clean rag to wipe around fuel cap prior to refueling.
Occasionally, we will also find that deteriorating fuel lines are responsible for clogged carburetors. The rubber material will break down over time and will begin to flake off in small particles that find their way into the carburetor.
Remedy: Replacing fuel line on principle when they become noticeably hard, brittle, or otherwise aged.
How do you clean carbs?
As we mentioned above, it is extremely common (albeit unfortunate) for people to end up paying twice to have their carbs cleaned. Similar to lacing and truing wheels, it’s a bit of a dying art and a lot of places seem to just fumble their way through it and hope for the best.
Cleaning the carbs involves removing the carburetor, disassembling, soaking in carb cleaning solution, physically probing passageways to clear them, and using compressed air or contact cleaner for the passages that cannot be physically probed. Disassembly and physical probing are the most commonly missed steps.
When asked how the passageways looked when they cleaned them, a lot of DIY’ers will, with a puzzled look, admit that they never even removed the float bowl. They instead simply soaked the entire carb in solution and in our opinion this method rarely, if ever, fully cures the problem. The passageways almost always need physical manipulation in addition to soaking.
The most commonly plugged passageway is the pilot circuit. The pilot jet in particular is responsible for symptoms 9 out of 10 times when we clean carburetors. The pilot circuit is what your motorcycle runs on up until about a quarter throttle. It is the first to clog up because it is physically the smallest. If your motorcycle dies when you turn the choke off the pilot circuit is most likely to blame.
Cleaning vs. Rebuilding
We frequently get calls asking for quotes on either cleaning or rebuilding carburetors, and think it might benefit some if we go over the differences in those two terms. Cleaning the carburetor is as described above, where generally speaking, most if not all of the existing parts are reused and nearly all expenses incurred are in labor.
Rebuilding the carburetor involves replacing many, if not all, of the replaceable parts usually by ordering a “carburetor rebuild kit”. In nearly all cases, our mechanics feel that these kits are an unnecessary expense. This is due to the fact that the kit mainly includes parts that very rarely need replaced.
Carburetor Don’ts
-Don’t adjust your carburetors yourself without a strong foundation on what the adjustments you’re performing do and how to do so properly. YouTube can be a great source of knowledge but it can also be a pool of misinformation. Do you research, ask the experts, and know your limitations.
-If you’re motorcycle is not running on all of it’s cylinders, don’t suspect synchronization. There seems to be a common misconception that carb synchronization will cure this symptom, but it will not. The carburetors instead need cleaned.
-Don’t try to clean the carburetor without removing the float bowl. This is a half-hearted attempt and simply spraying a solution onto/into it will not solve the problem at hand.
-Don’t park the motorcycle for extended periods of time without properly preparing it for storage. This will save you money, time, and frustration!
