Needle and seat on left is for gravity feed system,
units on right are for a system with a fuel pump
Needle and seat
The following pilot wrote this report on a
problem he was having with his engine. The problem is that he doesn't
realize that these two needles and seats are meant for two totally
different applications.
The smaller needle and seat is meant to be
used with a fuel pump, which applies pressure to the system, thus
the smaller hole.
The other needle and seat - with the larger
hole is for a gravity feed system, thus the larger hole.
DO NOT DO THIS to any engine that is set up to use a FUEL PUMP!!!!!
Sabre Ultralight Fuel starvation problem resolved
evening flight
Fuel starvation issue
Several weeks ago I changed the needle & seat in the carburator. The
issue, then, was fuel overflow/spillage after starting the motor. I
would never notice fuel overflow after a flight - only at initial
startup. I am unsure if it was overflowing during flight. A needle &
seat set was pulled from the old carburator that was on the motor when
I purchased it. At that time I also lowered the fuel level that is
maintained in the fuel bowl - changing two items at one time.
After the change, upon full throttle settings (take off), I would gain
about 30 to 100 feet of altitude and the motor would stumble just for
a moment. It would not loose more than a few hundred RPM but it was
certainly noticeable. At about 80% throttle it would run fine. There
was no overflow/spillage problem at startup.
A subsequent change was to increase the fuel level in the fuel bowl.
No spillage was noticed but the starvation issue remained.
Today I pulled the carb off of the motor and was going to put the
original needle / seat back into the carb. It was then that I
compared the original needle & seat to the old needle & seat. The
"good" needle & seat set on the left, marked as a 3.3 if I recall, has
a much larger hole for fuel to flow through it. The "bad" needle &
seat set on the right was marked with a 7.5 (I think). With the
larger diameter hole more fuel is capable of flowing through the
assembly when it is open thus keeping the carb bowl filled with fuel
for the motor's needs.
The next step is to adjust the float level a bit lower to see if the
overflow/spillage problem it eliminated.
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