User Manual

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Walbro Carb TUNE UP & Illustrated Guide
Note, this information is of a general nature only and does not
specifically relate to the DLA engines.
This information is for reference only.
Walbro carbs aren't too difficult to tune up if you know what you're doing. First of all, you need to know how
the carb works and how the settings interact with each other. About 95% of all the gas airplanes I've seen at
the field are somewhat out of tune. How can I tell this? Simple, at some point the engines "four cycle" in
flight. Two Cycle engines are not supposed to "four cycle" PERIOD. This is caused by a rich mixture that is
forcing the sparkplug to intermittently miss making it sound like a four stroke. This is not good. HOWEVER
the good news is; gasoline two stroke engines are very very tolerant of rich settings (most of the time) and
will run fine. You'll just consume a little more gasoline than necessary, and create a little more oil mess on
your plane. You may eventually foul your spark plug as well. So why do so many people leave their engines
tuned like this? Simple answer, the engine will start much easier when it's cold AND there's little or no warm
up time needed prior to flying. Those are pretty good reasons! But the fact is... the engine is not running like
it's supposed to.
LET'S BEGIN:
All Walbro carbs have their own fuel pump, a needle & seat controlled by a float diaphragm, a high-end and
low-end needle set, and some have chokes, some don't. There are so many variations of Walbro carbs, it's
ridiculous. I will restrict this editorial to the more common carbs found on airplane gasoline engines. This will
include the WA, WB, WG, WT, WL, WS, WTL and a few others. While there's a substantial difference in
these carbs, they share a common tune-up procedure.
FIRST and foremost, you need to know how the carb works and how the settings affect the running. Then you
also need to know how to make the adjustments. You also need to know what is a correct tune, and what isn't.
After that, it's free sailing!
Before you make any adjustments, you need to consider what's really going on and what part of the carb is
being used at that time. There are a lot of functions going on within the carb and one or more functions can
make the carb act strange. What could sound like a rich lowend needle setting could actually, and easily be a
float setting on the needle & seat! A stiff diaphragm will make it run rich too. It could also make it run lean.
The highend and lowend needles interact throughout the entire throttle range. So if you adjust one needle, you
will likely need to adjust the other.
Let's begin with looking at the components of the carb: