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.

So with that taken care of - time for a test flight...
Wind, calm, was from the East-NorthEast so into the wind I go.

Bare track from the GPS
(click for a larger image)

With the track data placed onto a street map and annotated

Looking east

Instrument readings
Temps are right in line - the right amount of fuel is being processed by the carburator
Click for a larger size

Some nice patterns in the harvested soy bean fields

Tractor tracks
A soy bean (or maybe corn) field that has yet to be harvested

Looking east towards Rockford and Belvidere
(click for a larger image with markings for the cities)

Radio tower
Only against the dark green grass are the guy wires visible.