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Author Topic: Engine very very lean for last 3 laps?  (Read 523 times)

Offline Dennis Toth

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Engine very very lean for last 3 laps?
« on: March 22, 2020, 02:19:30 PM »
Guys,
I have been working on different props for my El D with the Fox 35 and noticed that for the last 3 ish laps the engine goes very, very lean (really screaming) before it quits. It does this even when it is very rich. Not sure what is driving this. Throughout the flight the engine is consistent no run-a-way. Anyone have this happen and found a way to get a less lean cutoff at the end of the flight?

Best,     DennisT

Online RandySmith

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Re: Engine very very lean for last 3 laps?
« Reply #1 on: March 22, 2020, 02:31:37 PM »
YOu may want to try a cut off loop,  see if it works for you, If not  try another  uniflow tank, many times it will  go richer  when at the end of the run

Randy

Online Brett Buck

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Re: Engine very very lean for last 3 laps?
« Reply #2 on: March 22, 2020, 03:14:18 PM »
Guys,
I have been working on different props for my El D with the Fox 35 and noticed that for the last 3 ish laps the engine goes very, very lean (really screaming) before it quits. It does this even when it is very rich. Not sure what is driving this. Throughout the flight the engine is consistent no run-a-way. Anyone have this happen and found a way to get a less lean cutoff at the end of the flight?

Best,     DennisT

   I assume that this tank is rectangular, rather than tapered. If so, kick the rear of the tank out about 1/8".

     Brett

Offline Dennis Toth

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Re: Engine very very lean for last 3 laps?
« Reply #3 on: March 22, 2020, 04:41:00 PM »
Tank is 1" deep by 1 7/8" by 3 3/4" tin open uniflow, pinch corner, back corner kicked out 1/8". Cutoff loop does work if I wait until it jumps on the lean, lean step. Engine is upright mounted Fox 35, PA-Fox needle, stuffer backplate, stick in bypass, stock head, tube muffler with 3/8" outlet. Current prop is cut top flite spoon 9 1/2 by 6.3 (10 x 6 cut). Fuel is Byron's 10% with castor and Klotz (50/50) added to get to 27% total oil. Engine has no binding, no rod or shaft slop. Plug is Enya No. 4. Pretty straight forward normal stuff.

Best,   DennisT

Offline Dan McEntee

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Re: Engine very very lean for last 3 laps?
« Reply #4 on: March 22, 2020, 08:19:35 PM »
   If this is something new happening to an older tank that has worked well before, and has quite a lot of flights on it, you may have split the pick up tube some where along it's length inside the tank. This sounds crazy, but a quick, half tank test flight with the back of the tank against the fuselage like normal and see what happens, and if no change, shim the front out 1/8". The fuel will follow the tank, and if the fuel runs away from the pick up, keep fuel over any cracks, and it should quit cleaner.  Pop the back off and have a look if trying another known tank resolves the issue.
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Offline john e. holliday

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Re: Engine very very lean for last 3 laps?
« Reply #5 on: March 23, 2020, 10:10:18 AM »
In my experience this is normal on an open vented tank, even uni-flo.  But usually when using uni-flo hooked up the tank goes a little rich for me.   Good warning to not do any maneuvers and get ready for landing. D>K
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Online Ken Culbertson

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Re: Engine very very lean for last 3 laps?
« Reply #6 on: March 23, 2020, 11:00:22 AM »
If it is any consolation, both my Fox and OS 35s I used in the late 70's did the same thing.  I suspect it is more the tank than the engine.  I used it to time the kill loop.  I have speculated that what causes this the draw tube hitting foam and getting just enough fuel to keep it running.  I never paid much attention to what it did after the clover so long as it didn't do it too long!

Ken
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Offline Dennis Toth

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Re: Engine very very lean for last 3 laps?
« Reply #7 on: March 23, 2020, 07:43:32 PM »
Started looking at the setup and decided the one thing I did on this engine was to install the stick in the bypass. Pulled the backplate and found the stick had moved to the back side of the bypass. Since this is an upright engine the bypass is toward the circle center I decided to remove the stick. I don't think I will have any major problem with the burp and will see if the end of flight cut off is a little less screaming (I expect it to go lean once the Uniflow uncovers but not screaming). If this doesn't do anything (which could be the case) I will put a squirt of Armor all in the fuel to see if that cuts the foaming and give a cleaner cut.

Bests,     DennisT


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