Nickolas

Hi there,

My YS 170DZ works very well and has tramendous amount of power, it starts easily also. However at 3-4 out of 10 starts it will backfie causing a cracking noise that I suppose it is not very good for both the airframe and the engine. Also at the end of the day when I burn the fuel remaining within the engine it will backfire too. The same happens to the 160 but not as frequently.

What do you guys do to eliminate the backfire problem, except of using devices such as RC Cats or Japanese soft start products? Do you believe that if I carry on using standard plug heat I will have further issues? I ready of some cases of bent connecting rods, broken cam gears etc. Are these common to the YS DZ world? If backfiring was such a big issue why doesn't Yamada provide some special info in the manual suggesting the use of special glow heat devices etc. to overcome such problems? I just wonder...

Lookng forward to your practices to eliminate backfiring.

Thanks in advance,

Nikos

flyncajun

Nikos
the only way to prevent this without a Rcat delay Nicad ect.. is,, allow the motor to spin on start up for a few seconds before you add the glow.
This will allow the motor to blow any excess fuel out and start smoother
Bryan

Troy Newman

Close the carburetor all the way like you are trying to shut the engine down. Throttle barrel closed. Then apply glow and try to start it. with it in the "Kill" position

If there is a little extra fuel in the engine "partially flooded" it will burn off. When you have the carburetor open and it gives the engine too much air and there is a little extra fuel...meaning partially flooded it will kick when it starts.

I usually will pull my kill switch on the TX. This closes the carb completely. Then I try to start the engine sometimes it will actually start and run a few revs, and sometimes it will give a muffled soft pop. Then flip the TX switch back to a normal idle position and start the engine. Works every time.

Yes the delay glow drivers are good and I have one I use sometimes but its not needed and sometimes you can still get a kick. The way I do it the chances of getting a kick are extremely rare and even less chance of the kick over using the delayed driver.

And the new CDI doesn't kick at all.

Troy Newman
Team YS

tIANci

Troy ... what you are saying is that by closing the carb barrel the engine starves and when you start her properly its 'totally' dry and that eliminates the misfiring upon starting up.

apereira

The glow plug delay is the only way to ensure it will not happen, if you don't want to spend money on a time delayed glow igniter, I sugest you put a switch on your actual system and turn it on after the starter has been turning for a couple of seconds.

A friend of mine bent a valve on a backfired start, better safe than sorry.

Regards

Troy Newman

No closing the throttle barrel all the way and trying to start doesn't make it dry. It burns off the excess fuel only...

Its not dry at all. And will fire right up if you start it immediately after.

The excess or partially flooded situation is what causes it.
A just little too much fuel will cause the kick. By trying to start with the throttle fully close and no air or minimum air possible the excess will burn off.

then when you open the throttle to a normal idle position it will not be partially flooded.

By the way the 140L, 120SC, 120AC all did this too...its not just a DZ issue. All of the YS engines that are high compression and these engine listed above have the crankshaft ring on them giving a little stronger super charger effect.

The delay starter these guys are talking about means the engine can be more "flooded" before the kick happens. But if it gets to much of a excess load (more flooded) with fuel it will still kick.

Troy Newman
Team YS

Ryan Smith

My Feedback: (25)

I do similar to what Troy does, however I use hemostats, but the result is the same. I am still using a Radio South MKII glow driver that does not have a soft start, and I have not had any issues with backfiring, popping or anything. My motors always start within a few blades even on the first start of the day and the transition between the starter turning the motor over and the motor running itself is seamless. Unclip the hemostats and you're good to go.

riot3d

That's why you do not need to use a starter to prime the DZs, I just use my hand to turn the spinner both ways a few times just to activate the pump.

Adrian

Troy Newman

You are correct Adiran...

I don't prime the engines...Just start it.


The problem can come in sometimes when the model has been sitting in the sun. Pressure can build in the tank and the fuel will be pushed by that pressure.

Another reason it could get excess load of fuel (partially flooded)when you land the engine is hot. It can syphon fuel into the engine as it cools off.

Troy Newman
Team YS

MajorTomski

Just currious. Do you mean back fire or after fire? Back fire usually refers to flame coming out of the carb. Afterfire the flame is coming out of the exhaust.

Troy Newman

What the guys are talking about is more of a kickback.

When you try to start the engine...the starter will start to turn it over but the first time it hits compression it sires just a little early and never passes through top dead center It gets up to where it fires and kicks backward. Since out engines are mounted on rotation vibration dampening motor mounts the engine will rotate a large angle and sometimes hit the side of the model.

Its not really a backfire per se....its more of a kickback and the engine starts to run backward.

Another key to prevention of this is a strong starter motor. I'm actually running my starter now at about 18V, 4S lipo battery packs. It has huge muscle to turn things over.

The Kavan, Magnum and even the HD Hangar 9, and other HD starters from other manufacturers work very well on this voltage. How long the brushes on the electric motors will last at this voltage is another story. I have been doing it the 18V thing for about 8 months now.

The stronger the electric starter the less chance for kick back as well.

Troy Newman
Team YS

riot3d

In addition to Troy's aforementioned recommendation, if you run one of those heli fuel shut-off valve/ clamp on the outside of the fuselage, just clamp it shut right after your landing, that will prevent fuel from going back to the engine. I have also noticed most of the pilots will move the starter away as soon as their engine started, kickback usually happens at that time. If you leave your starter turning on the spinner for a few additional seconds, that will ensure the engine is indeed running, and will eliminate the kickback problem.

Adrian

tIANci

Troy I get what you mean ... Will do it when I fire up my YS160 the first time. One of my pal uses a switch and it works fine too but he will also use a pinch thingy that the helis use on the fuel line after flying to ensure there is no access fuel.

apereira

I use for starter a Kavan with a 14.8V LiPo, it actually moves a DA50 like a OS91, that much power, of course YS is very easy for this starter.
The reason for the kick back is compression as Troy said, but also due to preignition of the fuel mixture and the engine not having any inertia on the crankshaft (flyweel), once the engine is turning steady and glow power is applied a kick back will be very unussual, I only had back fires in the 160/170, never had one on the 120AC with starter.

Regards

mjfrederick

One thing to remember with the heli cut-off clips is that if the tank vent is not opened, pressure will build in the tank on a hot day. The way my setup is done instead of using something to pinch the line I disconnect the feed line to the engine where it comes outside the fuse, and the plug that line with the fuel dot that is on the vent/overflow line. This way the tank is not completely closed off and pressure can't build.

Nickolas

Hi there,

Thanks for the responses, first counter measure was already applied. I use the cut off clip by KS, it will be tested soon.

I have been using the Sullivan Dynatron starter, which provides significant torque but seems that I do not rotate the engine as much.

I will also try Troy's routine with the throttle barel fully closed.

Any other inputs are wellcome.

Nikos