Interesting Carburator problem

18 Mar 2005 Interesting Carburator problem

–> RV-List message posted by: “John Danielson”

I am going to relate an experience a friend of mine and myself had 2 years
ago. I wasn’t going to repeat this to anyone but I thought it might be of
interest to the RV community and could possibly save a life.

A friend of mine, Tim, from Douglas, WY had been looking to buy a 2 seat
ultralight to give lessons in. He had gotten his ultralight instructors rating
and had some students lined up, but needed a plane. He had been in contact
with a gentleman from Dallas, TX who had a 2 seat Kolb for sale. Tim told me
that the price seemed reasonable and he asked if I would fly him down so he
could look it over. Now Tim knows I am always looking for an excuse to fly, so
he was sure I wouldnt say no. Tim by the way is a private pilot with 4000
plus hours and has owned quite a few planes, including the Hiperbipe that he
owned at the time. We would have flown his plane but if he bought the Kolb, he
planned on flying it back to Douglas.

I had completed my RV-6 the previous year and had put 175 hours on her since
her first flight. I hadn’t had any problems with the engine or airframe, and
it performed as Van said it would. I am not a high time pilot, just passing
the 300 hour mark before we took off for Dallas.

The Friday we left it was clear, unlimited visibility, with about 10 knot NW
wind. This weather was predicted all the way to Dallas and was told it would
hold thru Sunday.

I left Casper at 8:00 am, flew to Douglas and picked up Tim and we were back
in the air by 9:30 am. Air was smooth and at 9500 ft we picked up a 30 mph
tailwind. We were cruising across the ground at between 225 and 235 mph. This
lasted all the way to Oklahoma. We landed at Weatherford for fuel and food,
time 12:30 pm MT. People there were very nice and let us have the courtesy car
to run into town and fill our stomachs.

We were back in the air by 1:45 MT and again we picked up a slight tailwind.
As we approached the Dallas area, I told Tim to keep a look out for other
aircraft as I had already spotted 4 or 5 that were within a couple miles of
us. He was already ahead of me as he too had been watching out for other
aircraft. The actual airport we were looking for was a little airstrip about
30 miles east of Dallas, sorry but I forget the name. In this area of Texas
there are private strips everywhere. The GPS told me where the airport was but
we were spotting private strips everywhere within 2 to 3 miles of our
destination. We finally arrived at 3:00 pm MT. Tim met with gentleman that had
the Kolb. He showed us the plane, pointing out the good and bad, then the 2 of
them went for a flight. Tim wanted some time to think over the purchase. Later
that night Tim told me that he didn’t think it was the right plane for him.

We got a ride into Henderson that night by a nice gentleman who was at the
airport flying his powered chute. He was also nice enough to pick us up in the
morning and take us back out to the airport. For his efforts we gave him a
ride in my RV as he would not take any money for his time.

Well we finally took off about 8:30 am and made our way back for food and fuel
at Weatherford. Up to this point the plane had been performing great. At this
lower altitude as was finally seeing climb rates and airspeeds I have only
heard others talk about.

While departing Weatherford the engine hiccupped once. Tim and I looked at
each other and he asked what that was? I said I didn’t know. The engine
continued to run smooth, the engine monitor didn’t show anything to be
concerned about, everything in the green. We both shook it off and we
continued on. Tim said he was going to take a nap and proceeded to fall
asleep. About 1 hour into the flight I noticed the CHT were rising, not
critical, 355 F. I richened the mixture a little and the temps came down. My
hottest cylinder usually runs about 315 to 320 F. I was running 2500 RPM, 20
MP, crusing at 8500 FT. I have affixed pitch wood prop that is perfectly
suited for the O-360 F1A6 I have in my plane.

I kept an eye on the CHT and slowly it started to climb back up. I would again
richen the mixture and CHTs would come back down. Outside temp was about 85 F.

This continued until the engine began to run rough when the CHT climbed to 355
to 360 F. If I richened the mixture the problem would go away. If I kept the
mixture where it was at and turned on the electric fuel pump the problem would
go away- for a while.

Tim finally woke up and I explained the situation to him. We were over north
central Colorado by know and we talked about landing to see what the problem
was. The problem was that by know I had the electric fuel pump running
constantly, mixture was full rich and I was slowly having to reduce RPMs. We
were still caring 2400 RPMs and are cruise speed was only down to 165. I
usually cruise at 180 MPH.

We were now over Wyoming and only about 50 minutes from Douglas. Tim suggested
I turn to the west and get over I-25, as the terrain starts to get rougher the
farther we get to Douglas. Again we talked about landing and the nearest
airport and checking things out. I told Tim that if we land we are probably
not going to takeoff today, unless we get lucky and find the problem. We were
still in the air, plenty of daylight, plenty of fuel (reduced throttle) and we
were still making 145 mph across the ground. RPMs were now down to 2200. Of
course we were constantly aware of our position and were looking for fields
and roads to land on if we had an engine failure.

Needless to say we made it to Douglas and landed without incident.
At Tims hanger we removed the cowl and I removed the carburetor. Tim checked
the gascalator, nothing. I removed the brass screen from the fuel intake at
the carburetor and found the problem. There was a circular piece of cloth
right at the fuel inlet to the carb. I knocked this out of the screen, when I
touched it I found it wasn’t cloth but fine grains of dust, lint, etc. not
sure what it was. It had blocked the opening to the carb enough to actually
distort the screen by inch. I am sure if it hadn’t been for the electric
fuel pump we would have had to set down and hour or 2 earlier.

Nothing was found in the gascalator or the fuel tanks.
I had purchased the engine used but had not taken the time to tear into the
carb. Of course I had flown the plane more than 175 hours until this problem
arose.

We cleaned the carb screen, put everything back together and I made a test
flight around the airport at Douglas. Everything was fine so I headed back to
Casper-25minutes, and landed without further incident.

The next day I went over the fuel system but could find nothing wrong. Maybe I
picked up something during the fuel stop at Weatherford, I don’t know.
Maybe this will encourage those that haven’t looked at this screen to do so
know. Those that have bought a used engine may want to also clean this screen.

Tim and I wonder if we made the right choice in continuing on. There is know
doubt that it would have been ok to land and check things out. If
circumstances had been different, such as low on fuel, weather deteriorating,
etc. I am sure we would have found the nearest airport and landed. I know
there are those of you out there that think we were insane for continuing on,
and that is your choice. I am just writing this to give us all something to
reflect upon.

John