Hi everyone, pretty new to rc planes , but i have been running cars for some years now so i am familiar with carb tuning. I have a pulse xt40 with the evolution 10 gx engine, i would like to call this my nemesis! I have several issues with this great engine, on my maiden i damn near crashed once the plane hit 3/4 throttle the alerons would fludder and then straighten. I fixed this issue. The ignition was bad and throwing interference, hh was great and replaced it. The issue i have now is that in a dive the engine looses power and wants to die. I have checked my tank, the clunk and lines all look like they are supposed to, this happens at full tank or half. Normal level flight is fine climbing is fine. I can also re create this by lifting the plane up and tipping it forward. I am using the correct type of fuel line, and clunk. Also i am running a 12x6 prop. Thanks for the help

Sounds like the pickup line in the tank is stiff allowing the clunk to come out of the fuel.

In a dive the fuel goes to the front of the tank anyway is your fuel lines short? Does that engine use a walbro carb

Hi!
All planes /engines should be able to dive straight down for one to two seconds without the engine cutting out, If you cannot do that something is wrong!
How is you tank set-up?
Most R/C tanks are set up with two fuel lines, one is going to the carb and the other straight up inside the tank is for pressure /telling when the tank is full. The fuel line going to the carb should be so long that the clunk is set apprx 10mm from the back of the tank.

A better solution is to use the two clunk lines ,called "Uni-Flow" (one going to the carb and the other for pressure) running side by side,the pressure line 10-20mm shorter then the line going to the carb. The third line is going straight up as usual and it's for telling when the tank is full.
Having the pressure below the fuel surface makes a more even pressure distribution for the carb and thus makes the carb setting more even.

This engine comes with a plastic filter clunk and neoprene line. The neoprene line they supplied along with the weight of the plastic cluck caused a similar problem for me. The clunk would not drop and slide inside the tank resulting in deadsticks.
I removed the supplied neoprene line and plastic clunk and replaced with Tygon line and a brass sintered clunk. The sintered clunk is much heavier than the plastic filtered clunk yet still helps prevent sir bubbles in the line and the Tygon line is (for now) more flexible than the supplied neoprene. I have my tank set-up with two clunks, fuel dot , carb feed with outboard filter and the pressure line.
Using the supplied neoprene line on the exhaust to the tank is recommended due to the heat.
Also try and keep the ignition & ignition battery in one place away from the reciever and keep the wires away from other servo wires and metal control rods. If you have to mount the ignition battery away from the ignition keep the wire away from other wires and metal rods.
Once you have the engine broke-in(many,many tanks) you can start to tune the low and high speed settings on the carb and get it running real nice.

Thanks guys for the prompt responses, I will check all the things you have brought up, and yes i am running the stock clunk and supplied fuel line. It did appear a bit stiff i was hoping it would soften once in the fuel. I will post my results!

The 10GX uses such a small amount of fuel and the vibration of the tank will wet the supplied felt clunk that I doubt that the tank is the problem to engine dying on down lines because of fuel starvation. Is it possible that that the engine is being flooded? The gas carb on the 10GX has does not have a pump but it does have a regulator so it may be that the regulator is not functioning properly due to a contaminate or other problem.

This can likely be confirmed by filling the tank full and shortly after starting, pointing the nose down while holding the plane. It should not starve for fuel with a full tank. If it breaks into four stroking and then dies... it is likely flooding, if on the other hand the RPM's increase and it screams and dies... it would be dying too lean.

Richen the high speed needle a little. What I think is happening is that the engine is unloading while in a dive and leaning out. My guess is that it sounds like it is picking up RPM and then sags.

Good points made as well
Try this before changing anything. Fill the tank halfway and fly it. Go inverted, do some loops, ,climbs, knife-edges and see if the engine sputters and wants to die. If so it's the carb line inside the tank. If it still only does it in a dive and the engine does speed up as mentioned before sputtering then your high end is a bit lean. Open the high speed needle a click and fly it again.
I'm still placing my bet on the clunk and line as I've been there already with it.

The OP outlined that it dies in both down line and when held in a static down attitude. Unloading would not come into play when static. What would come into play is the gravity force of the fuel... hence why I'm wondering about a regulator problem.

Well I went through the plane last night and checked the tank (2 line setup) and the stock fuel line and stock clunk had not soften up as Iexpected. So I changed the line to Tygon and a heavier clunk, I also shortened it a few mm. Doing a static test (tipping the nose) it appears to be better but the RPM's do pick up a bit. However if I increase the idle just a bit she holds pretty steady, I assume this is do to the increase in pressure from the exhaust, cause more even fuel flow. Today I will go to the field and test fly wish me luck!

Hi!
Be sure you use silicon fuel lines and not Tygon! Tygon fuel line is used for gas engines. Tygon is way way to stift to use in small glow fuel tanks.

OK here is an update,


I changed the clunk line to silicone (shortened up a bit) added a heavier clunk, moved the fuel filter closer to the carb to lessen the chance of bubbles, adjusted to factory settings. Started the engine and unless i increase the throttle wile dipping the plane into a simulated dive, it stutters and dies. If i increase the throttle giving it a bit more pressure on the exhaust port it does better. All in all not very impressed at this point.

As you are you using the new Evo 10 CC GAS engine silicone fuel tubing is the wrong stuff to use and Tygon (yellow) is correct as stated earlier.

Silicone will swell after being exposed to gas for a bit and cause all sort of issues!

Bill S.

You mean Tygon line ...right?
Did you pressure check the tank for leaks especially around the stopper?
Did you seal up all the sections and the bolt on the muffler so it doesn't come loose and/or leak?
How is the low speed for transition from idle to mid-range and idle to full throttle ....what does it do?
How is the high speed for full throttle/top end?

Yes I meant Tygon, I fixed the typo as well...

ALSO there is a huge thread on that engine here:

http://www.rcuniverse.com/forum/m_11..._1/key_/tm.htm

Bill S.

How does the exhaust port factor in?

You do have a vent line to the thank, not to a muffler right?

-

You should try two things...

1. - Richen both needles about 1/4 turn and try flying to see if this makes a difference.

2. - Put a loop in the line to slightly lengthen them.

Normally we WANT the lines to be as short as possible... however during a downline air WILL enter into the clunk unless the clunk moves forward with the fuel... something that Tygon is not very good at, so the clunk tends to get uncovered a lot.

That produces air bubbles.

Normally air bubbles get sucked out the needles so quickly that when the plan is throttled back in a dive you barely notice them, but if the engine is too lean you end up with a deadstick.

A fuel line loop leaves more fuel in the line for the engine to use during downlines.

3. - Run the engine nose down while you hold the plane and check for problems.

Does the clunk go to the front of the tank when the plane is tilted down? Tyson is somewhat stiff.

clarification "Exhaust port"I mearly ment the barb on the muffler, sorry about that. Also with the supplied fuel line and clunk it has little to no movement in the tank due to being so stiff. So I replaced it with fuel line for gas engines from my local hobby shop I will have to verify if it's tygon or silicon (Currently at work). However with the new line and heavier clunk I now have movement. I will do another pressure test on the tank just to verify a good seal. I will also try a longer fuel line to see if that helps the issue. It is rather odd on the bench she runs pretty good than when i get to the field it's a dog, and it causes me to not want to fly due to fear of crashing.

How many turns out is the high speed needle?

In 35 years of R/C flying I have never set up a tank so that the clunk moved to the front of the tank. If someone was to do so it will get stuck there. The fuel will be moving around in the tank enough to keep the engine supplied provided it is not set too lean. Holding the nose down while the engine is running is a useless test. Set the tank up with 1/8" Tygon tubing leaving about 1/4" clearance between the clunk and back of the tank and then set the needles to manufacturers recommendations. This is not a glow engine so not a big RPM difference between rich and lean so I am sticking with my original assessment that it is just set too lean.

Another test to run... after fueling, when pulling the fill tube off the fuel dot... note if there is any pressure in the tank pushing fuel back out the dot until it is plugged. If so, it indicates the vent line has a kink that many times will allow filling the tank, but is closed otherwise and will cause negative tank pressure.

While not always or usually done, there are plenty of workable ways of doing this.

I don't bother though as there is something to be said for simplicity.

As you say the engine should handle downlines if it is not overly leaned.

Nonsense, his engine is not a usual gas engine setup. It requires tank pressure to function correctly.

A nose down test while on the ground will both help establish if the engine is too lean and also help reveal other potential plumbing issues.

There is no vent line used for this engine, rather tank pressure is called for according to the manual.

That may be part of the problem too.

The engine does appear to have a pulse port, but the manual tells the user to install a muffler to tank fitting for pressurization.

A normal gas pumper should not need tank pressure, but if this engine is not getting required pressurization that may lead to the symptom he is seeing.

All tanks have a vent line... in your case the vent line is also the muffler pressure line.