Author Topic: Engine goes lean during the second half of the tank???? (Read 547 times)

frank mccune · « **on:** May 16, 2020, 07:20:38 PM »

What would cause an engine to go lean during the second half of the tank? Here is the combination:

LA .46 on muffler pressure mounted sidewinder on a profile.
Uniflow tank fueled with 5% nitro and 25% castor.
No leaks in the system.
Prop 11-5".
NVA stock OS in a conventual front venturi.

This combination has always worked to perfection until today with a launch speed of 9000 rpm.

This mystery has us stumped! Could it be burned caster oil in the engine as this engine has had many flights with only castor oil as a lubricant?

Suggestions/ Comments?

Tia,

Frank McCune

Brett Buck · « **Reply #1 on:** May 16, 2020, 07:34:17 PM »

Quote from: frank mccune on May 16, 2020, 07:20:38 PM

What would cause an engine to go lean during the second half of the tank? Here is the combination:

LA .46 on muffler pressure mounted sidewinder on a profile.
Uniflow tank fueled with 5% nitro and 25% castor.
No leaks in the system.
Prop 11-5".
NVA stock OS in a conventual front venturi.

This combination has always worked to perfection until today with a launch speed of 9000 rpm.

Seems like *vastly* too much pitch, but remove the pressure line.

It *does not* like drawing fuel with this combination (2000 rpm slower than nominal), but pressure into the uniflow vent has caused exactly this issue on a number of occasions for me.

Brett

GERALD WIMMER · « **Reply #2 on:** May 17, 2020, 05:51:19 AM »

Hello Frank I have seen this happen before when a LA46 runs fine till the 25 % caster builds up as carbon on the piston skirt. It slows half way into the flight as the motor warms up . Running rich and slow on an 11x5 makes this effect worse. Take the muffler off and you will have a nice black piston , next pull it down and clean off all the varnish and swap to a fuel with 50/50 synthetic and caster oil unless you are willing to do a regular decarb/remove varnish. Running it a bit faster on a lower 4"pitch prop without muffler pressure may also give a more reliable run.
Regards Gerald

frank mccune · « **Reply #3 on:** May 17, 2020, 07:48:34 AM »

Hello All:

Many thanks to all who answered!

The engine in question is an OS .40 FP and not a LA .46 as I had stated. That plane and engine combination has more than 500 flights on it.

I suggested that the prop may be a bit too much for the .40 and perhaps a ten inch prop may be a solution. The owner was very resistant to try a ten inch prop and a synthetic lube. With a bit of arm twisting, I may be able to convince him to change his mindset. Lol

Stay well,

Frank McCune

frank mccune · « **Reply #4 on:** May 22, 2020, 01:15:58 PM »

The problem has been corrected by running 6 three ounce tanks of 10-10 5% nitro through the engine. After many, 500, flights, of using 25% castor oil, 5% nitro and 5% acetone through this engine, I guess that the piston/sleeve got a bit of a castor varnish on them. The owner will not use a synthetic oil in his fuel.

Thanks for the replies,

Frank McCune

RandySmith · « **Reply #5 on:** May 22, 2020, 03:43:11 PM »

Quote from: frank mccune on May 22, 2020, 01:15:58 PM

The problem has been corrected by running 6 three ounce tanks of 10-10 5% nitro through the engine. After many, 500, flights, of using 25% castor oil, 5% nitro and 5% acetone through this engine, I guess that the piston/sleeve got a bit of a castor varnish on them. The owner will not use a synthetic oil in his fuel.

Thanks for the replies,

Frank McCune

Frank
the owner should learn to use part synthetic, My pinned article at the top of the forum tells exactly why
ALL castor fuel will ruin any engine over time

Randy

frank mccune · « **Reply #6 on:** May 24, 2020, 10:49:04 AM »

HelloAll:

Today, my flying mate experienced the SAME problem with his ST .56 I told him that I wanted him to run 50-50 lube through his engine and he agreed to do it. This engine has been run on the same fuel, 5% nitro, 25% castor oil and 5% acetone for many years. It starts on the first flip every time and runs like a fine watch. However, the needle adjustment to get a good run is becoming quite elusive.

I was very impressed that he agreed to give the alternate fuel a chance! I hope that it is successful. It is sometimes difficult to change people’s

Thanks for the help,

Frank McCune

Author Topic: Engine goes lean during the second half of the tank???? (Read 547 times)

frank mccune

Engine goes lean during the second half of the tank????

Brett Buck

Re: Engine goes lean during the second half of the tank????

GERALD WIMMER

Re: Engine goes lean during the second half of the tank????

frank mccune

Re: Engine goes lean during the second half of the tank????

frank mccune

Re: Engine goes lean during the second half of the tank????

RandySmith

Re: Engine goes lean during the second half of the tank????

frank mccune

Re: Engine goes lean during the second half of the tank????