Needle richness will
have a great effect on fuel mileage.
BUT, having said all that, it will also have a great effect on whether
or not you come back under your own power or under the sled pulling yuz
There are a few things to consider when "tuning in" a sled's fuel
settings. I will try and hit a few key factors that may or may not be so
1) The Main jet effects the mid-range settings and effects it in a big
way. I will explain... The jet needle is a tapered rod. This taper is
directly related to how much fuel it will let the MAIN JET flow.
taper = less flow---> thinner taper = more flow..
2) The jet needle, from idle to about 3/4 throttle position, is INSIDE
the MAIN JET.. So, the taper is very important in how much flow is
coming from the MAIN JET, but so is the throttle
3) As you raise the jet needle via throttle opening, the main jet
becomes less obstructed/blocked and allows fuel to flow around the jet
needle.. This is your part throttle fuel flow control.
Your pilot jet is
still a player but the more the throttle opens, the less it is a factor.
4) Since the main jet is a major player in the part throttle fuel flow,
one should ALWAYS "dial in" the WOT, main jet, circuitry BEFORE EVER
adjusting the jet needle/part throttle circuitry.
WHY?? Because the main
jet effects part throttle fuel flow and the jet needle has little to no
effect on WOT fuel flow.
5) Since #4 (above) is not often understood, many tune in the part
throttle running , first, and then adjust the WOT , after.. This can lead
to ,part throttle, engine failure or a very poor running engine, OR
Again, always tune in the WOT circuitry before ever adjusting the
part throttle circuitry.
When do you know when you have the part throttle circuitry adjusted
This is a good question and somewhat difficult to answer..
a) If you are looking for MAX fuel mileage then this gets a bit more
tricky. Max fuel mileage also means min, or very close to it, fuel flow
in the part throttle circuitry. Since the jet needle is tapered and this
taper varies with throttle opening, you can get into trouble because you
never know ,exactly, what throttle position you are at and the air-flow
via air-box, is also a variable and is a major player in the fuel that will
flow from your carb. So, be careful when shooting for max fuel mileage.
My suggestion is to not strive for max fuel mileage and concentrate more
on "SAFE" but "RESPONSIVE" part throttle running. I tune in my part
throttle as so: If I can get in or out of the throttle at any throttle
position and have the engine respond without hesitation, I have my
Sometimes, with this desired setting, I will hear a
"gurgle" which would lead me to believe that I am over-fueling the
engine.. BUT, it is best to ignore this "gurgle"!
WHY? Because the
engine is at the responsiveness level I desire.... I have no hesitation
when getting in or out of the throttle! So, the "gurgle" I hear should
be ignored since the engine is running as desired.
How do I know if I am Lean or Rich ??
a) USUALLY, any lean condition will present itself as a "BOG". So, one
should listen for this low droning, bog when adjusting.
b) USUALLY, a rich condition will present itself as a "gurgle" or
"sputter" and with this comes a lack of throttle response.
PILOT Circuitry: This circuit is often way over-rated. The pilot circuit
is really only a player from idle to about 1/8th throttle opening. If
you are having issues above 1/8th throttle, the pilot jet is not a major
If you have a high or hanging idle, usually, this points to a
pilot jet that is too small.
If you have a very low idle that can not be
adjusted via idle screw or air/fuel screw, then this points to a pilot jet that is too
Hopefully this clears up a few things.