Hi all,

I am new to this forum and thought I would seek your guidance.

I have an Evolution .40 that has registered more than 30 flights in my trainer. I have an Evolution .46 with about the same number of flights in my Sport .40. When new, both started right up the first time and have operated flawlessly since. Both were mounted right side up.

I recently removed the .40 and mounted it in my new Seagull PC-9 ARF. The PC-9 calls for the engine to be mounted inverted. I have had nothing but problems with the engine since mounting it on the plane inverted.

The engine was tuned right side up on a test stand before mounting it on the plane. When installed (on the plane) inverted, fuel dripped steadily from the carburetor and the engine would not start. The engine had to be completely re-tuned before it would start (engine was still not running right - would stop after 30 or so seconds of operation). The fuel used in the .40 is the same fuel that I use in my .46 which fly’s great.

The fuel tank was mounted much higher than the high-speed needle valve, so it was repositioned. It is now, as close to needle valve center as the plane frame will allow. The plane is fueled with a Du-Bro Kwick-Fill Fueling Valve, mounted on the top of the topside of the plane, in front of the canopy.

Yesterday, finally after many minutes of adjustment, I got the engine (still inverted) to idle at 2800 rpm and lean out at 13,500rpm, then richened it a bit. The engine ran for about 5 minutes, throttle being moved from idle to full throttle with no hesitation. I then quit tinkering since the engine seemed to be running great once again.

Today, I tried to start the engine and it immediately hydro-locked. Fuel was once again, slowly dripping from the carburetor. I removed the glow plug, and blew out the excess fuel (engine was now right side up) and made sure the engine would turn over by hand. I then turned the plane right side up (engine inverted) and tried to start the engine again. It immediately hydro-locked. This sequence was repeated twice setting on my workbench. Very frustrating.

The only advice that I received (other than repositioning the fuel tank) from flyer's at my field is to give up with the inverted engine. Mount it right side up and fly away. Can someone give me additional guidance?

Hotlanding,

It seems you are OK in your tank set up.

One method that may not seem so attractive, but at least will keep you flying, is to start the engine with the plane sitting inverted in a stand. Once running fine, just flip the plane over one wing and put it down to the ground.

In general I think it is harder (!) to hydrolock an upside down engine. Why? Because fuel tend to drip straight out of the carb rather than down the crank shaft. It seems strange your problem.

One potential cause could be over filling the tank, hence fuel pressures into the carb. A guide line can be to watch the pressure tubing from the muffler. Once that starts to fill it is time to quit running the fuel pump and maybe even reverse it for a second or two.

One other idea right out of the blue: Have you checked your piping to ensure that the line to the carb actually is the line from the clunk? If you mixed those up it could potentially makes strange things to happen.

Well, at least some suggestions to work with. Almost all my planes have more or less inverted installation and they seldom hydro lock. For me it is more usual that I end up trying to start a dry engine.

Anyway, best of luck!

/Fredrik

Hi Fredrik,

Thanks much for the response. I just tried your suggestion of starting the engine with the plane inverted (engine right side up). The engine started right up six out of six times, idled at 2800rpm and throttled up to 13800 rpm. Each time I tried to turn the plane over, the engine stopped as soon as the plane was sideways. I also verified that the klunk line was the line going to the engine via the kwik-fill fueling valve.

Will continue trying...

Thanks again,

Rick

Fredrik,
I ran Sup .90 inverted, Saito 100 inverted, ST .60 inverted, bunch of little motors .15, 25, .32 inverted.
all you need to do is

1. Watch your tank and fuel lines. not too far from motor and not too high on the carb.
2. I use a Dubro filler with a two line tank. Lines come out of the tank go down to the filler
come back up to the carb all in less that 7-10 inches of fuel tube.
3. Run muffler pressure.
4. Run a new plug, dont be cheap on plugs it's not worth it for the motor to die on final when the motor is
pulled back to idle.
5. Sometimes you will get siphone affect on the carb. do one of two things
A. Immediately upon shut down defuel the tank
B. If you dont want to do that use a hemostat to shut off the fuel.
C. Close the needle valve and reset and tune everytime you run up.

Thats all I can think of.

JDS

I have a easy fix
If you are running a fueling valve
get a extra fuel probe ( the one that sticks into the fuel valve)
and stick it in right after shutdown.
That blocks all fuel to the carb. I just plug the probe with fuel line and a screw.

Hotlanding,

-Try to run the engine warm before flipping the plane. Maybe a minute or so on medium throttle.
-Also try to remain 1/3 rpm, lets say 4-5000 rpm when flipping.
-If that does not help, try changing the plug

It should not stop. If it stops when turning it, it would not function in air either.

One last installation suggestion: Check the pressure line's pipe in the tank, that it points upwards when the plane is up right. If it points down you can get back pressure when releasing the gas, which can make fuel pour back to the silencer. The silencer builds an over pressure in the tank which has to go somewhere. In that case the silencer fills with fuel, which most of it blows out, but what's left may pour into the cylinder after stopping the engine. Also If the piping is correct installed, you may need slightly less needle opening when plane is up right due to the above statement of back pressure. In other words screw the needle valve in a little before flipping the plane.

One other suggestion that I had to do with my heli that had the tuned pipe mounted higher than the cylinder, hence fuel ran down after landing. I removed the plug and ran the starter for a couple of seconds. That cleared the lock.

/Fredrik