Cambo

My Feedback: (2)

Today was the big day and i finally got to open the box for my sk 90. Spent the day getting it fit into my funtana x50, was a little tricky but got it in, and finally got to fire it up. All i can say is wow. It is running great right out of the box, beautiful idle and transition. I am running a zinger 15-6 as recomended and an os 8 plug. This thing throttles just like a 4-stroker and i am so excited. With only one tank through it and the needle set very rich, it has already passed the power of the fl 70 that was once in the plane. The engines appearance was beautiful out of the box and i noticed lots of high quality items on the engine. It even came with the option of either a remote or front hs needle valve. The only thing i found strange during break in was the manuel recomended 1-3/4 turns out to start wich was very lean.

Ernie Misner

Ed Moorman has mentioned that the SK has a very hard ring and requires following the directions on the breakin. Also, IF you do try to prop it for revs the transfer ports are fairly narrow and it will go lean and hot.

Great engines it sounds like!

Ernie

Ed_Moorman

My Feedback: (1)

Keep the 15-6 on it for a gallon or so. My 2 have run great. I am runing an OS #8, 10% Omega castor blend fuel. I have tried several 15-6 props, Zinger, APC, MA and MAS, but am using the 15-6 Master Airscrew Scimitar. Both of mine have been an old, rebuilt, trash can Ultra Stick 60 that weighs over 8 lbs. Great vertical climb, pulls like a tractor. The engine will keep getting stronger for about 3 gallons of fuel.

My first engine which I took out to air break-in the second, is going in a new Twist 3D 60.

By the way, both engines usually filp start with one back flip. I don't recall ever using a starter on either of them.

I did have a minor problem with both in that the carb started sticking. I took the barrel out and, under magnification and a bright light, I notoced the angled slot that cams the barrel out and in had the edges flared up on the ends. These flared up portions dug into the aluminum carb body, causing it to stick. I would think this is from using a dull cutting tool. I took a small file and touched up the rounded ends of the groove and the carb now works smooth as glass.

Cambo

My Feedback: (2)

Thanks Edd
I am using a zinger at the moment and everything seems to be going great. Can't wait to get her leaned out. Will put a few more tanks through tommarow and will probabley fly her on wensday. I fergot to add that the idle was beautiful for the first tank of gas. My plane should come out around 6.5-7 pounds.
I actually couldn't get them to fip start today and had to use a starter. The backflips would just not pop back for somereason.

Ed_Moorman

My Feedback: (1)

A back flip start requires knowing the technique, and I'll admit, it can seem like a ritual to some people. I open the throttle and choke 3 times either by holding my finger over the carb or by holding my finger over the exhaust. When you cover the exhaust, it may take more than 3 flips to get pressure into the tank and force fuel up to the carb, depending on the length of your fuel line. I then close the throttle and flip the prop 6-8 more times to get fuel up into the cylinder. Normally, you can hear a "squishy" or wet sound after a flip. Sort of a pop-squish. This means it is wet. At this point, never, never flip the prop through compression with the glow driver hooked up. The engine is on the edge of being loaded and it will try to KILL your finger. If you put the prop up against compression, then slap it backwards, bouncing it off compression, it normally starts up in one flip.

It takes a little practice and some engines require more or less chokes. If you have a spinner, you can just twirl the spinner backwards for a start. Besides not having to get out a starter and grind away on your engine, it does look pretty cool when you prime, flip a few times, hook up and snap the spinner once for a start.

The key is to get the engine wet. Then when you bounce off compression, it will fire, kick back and run forwards. The key it to never pull the prop through top dead center. I have used this technique on big Super Tigres and Mokis. I have owned many of these and never used a starter. I do use a heavy glove. Usually, I slap the prop backwards hard enough to be uncomfortable on a bare hand and nylon props can cut.

buzzingb

My Feedback: (2)

Ok lets talk performance what rpm with what prop??

14X6 rpm=

15X6 rpm=

16X4 rpm=

We need some performance figures to help figure this motor out.

AMB

Ed the back flip technique is at least 100 years old the old one lung bangers marine engines with make and break ignition were started
this way with a flip to the fywheel I understand they would also do this backwards to obtain reverse running no transnission\martin

Cambo

My Feedback: (2)

Thanks edd
You now what i wasn't doing was after i primed it, i didn't flip through a few more times to get the fuel into the cylinder. I will try again today.

Buzzingb
I havn't tried all of those props but after reading through the sk engines thread i can tell you something about them
The 14-6, at least from what i have heard, is not enough load on the engine, and in the air it leans out and quites. I believe you should be shooting for 10,000 or below on the ground and that prop exceeds that.
The 15-6 is supposed to turn between 9500 and 10000, i will get some tach numbers today
I can't tell you about the 16-4
I know these numbers sound low but but this engine is not meant to scream. It really throttles nicely and doesn't take along time to rev up like most 2 strokers

XJet

Since few of my models have spinners, I hand start most of them and (because I'm using APC props -- aka "razor blades") I always flick them backwards so that my fingers only contact the relatively blunt leading edge of the prop.

They usually start first flick -- and run the right way, even though I *am* flicking backwards through TDC.

As you point out though, getting the prime right is important.

And, even if they do start running backwards, careful manipulation of the throttle causes them to stop running backwards and suddenly start running forwards -- as if by magic (lots of folks are amazed by this).

Cambo

My Feedback: (2)

Edd I followed your prime method and it worked like a charm. Started up on the first flip. With 2 tanks through it we are seeing about 9000 extremely rich on the 15-6, not 4 cycle rich but a very rich 2 cycle. My idle is about 1800 and it is still at the factory setting. Transtion is beautiful and it transitions from idle to full throttle instantly. The only complaint i have so far is it shakes my little funtana like crazy at idle, but above idle the shaking goes away. I expect it to get better as i break it in. I am going to be flying the plane tommarow.

Cambo

My Feedback: (2)

X-jet, thats i good laugh, APC props are like razor blades. I have about 5 cuts on my hand from them.[:@]

MGREENBERG

iIhave 2 sk engines, a sk 50 and an sk80.
Bith were sebt out today for repair or checkout.
My sk 80 has only given me one complete flight out of 10.I had it VERY rich that flight!!
It always ran hot and with a pitts muffler it didn't provide enough pressure to draw fuel until I blocked one exhaust stack.Used a 13x6 mostly.
Had to dead stick it every flight.and the motor never seemed to power my 60 size Extra with authority.
The sk 50 never ran right until I replaced the stock muffler,which separated inflight,with a Max muffler.Then it ran great for maybe 30 or 40 flights.
Now I have either or bearing or the crank bad in it.The prop is hard to turn.Used an 11x4 and 11x6.Ran weel with the Max and used very little fuel.I could get 20 minutes out of an 8 oz tank,easy.with mostly high trottle settings.
Anyone had these problems?

Cambo

My Feedback: (2)

MGREENBERG, sorry to hear about your bad luck with the sk 80
I would read through the sk engines thread, it has alot of info on it. A lot off people had problems with the engine leaning out in flight and it turned out that they were underproping it. If your engine is exceeding 10,000 on the ground than that might be the problem. Try maybe a 14-6 or a 14-8. Remeber, these engines are ported for big props, not speed.
Good Luck

NM2K

My Feedback: (14)

I feel sorrier for the SK engines.


Ed Cregger

RCVFR

My Feedback: (7)

prgonzalez

I need some help in here. I started my SK 90 today for first time. I am using a TF 15x6 wood prop. 15% Nitro 20% oil (syn + castor blend) power master fuel. Kangke pitts muffler for SK-90. Ambient temp 80-F and humidity around 85%. Center of tank is aligned with engine carb. Engine is at 90-degree. (Horizontal).

First fire up. The engine had problems going beyond half throttle. Seemed to run okay below half throttle. I also saw the oil was coming out too dark (black - I know, metal to metal). So, I plugged one out of the muffler and then the engine was able to go full throttle.

I did the break-in as recommended. However, I had trouble to get it rich. The HS needle was not causing any RPM drop as expected. I went more than four turns out and no drop in RPMs. I was consistently getting only 7700-RPM. I tried closing and opening many turns and the variation was only 100 RPM.

The pinch test...

Pinching the line did not cause a raise or drop of RPM in short time. The engine continue running at same speed for about five seconds and then started to die. It did not die as soon as I pinched the line. So, I assumed it was a bit rich. But, transition from idle to full was okay. Idle is about 2300 RPM.

After about five tanks dealing with the engine, I flew the plane. The engine seemed to be rich at ground, again 7700-RPM. But, after five minutes of flight, I had to land because I heard the engine coughing. It did not dead stick, but it was coughing. When I grabbed the plane, I felt the engine too hot. So, I opened a bigger hole in the cowl in front of the cylinder. The hole now provides air to the whole cylinder. Before, it provided air in about 75%. The hole in the back of the cowl is approx. 8 sq-in. I think is big enough.

So, second flight...I took off and flew at half throttle in circles paying close attention to the engine sound and performance. No aerobatics. After five mins. the engine was coughing again and I landed. The engine was again very very hot. I am able to see the top of the cilinder was cooking castor oil and has some dark stains now. The exhaust oil was also dark, not good. The muffler is still plugged in one leg.

I am not sure if I read about bad tappered needles that were causing adjusting issues on this engine, or perhaps I am mistaking this issue with another brand.

Okay, any ideas?

Pedro

edited for typos

Kweasel

My Feedback: (29)

Put a smaller prop on it.

Turk1

Hi Pedro,did you ever play with low speed needle from factory settings?I thinkyou need to open a little on LSN to allow HSN to make your engine richer.I have heard some people ,their SK s need some more LSN settings than factory for proper running.

RCVFR

My Feedback: (7)

The symptoms you describe can be the result of too high nitro. My ST 2300 runs great on 5% and runs as you are describing on 15%. My SK 50 likes 5% much better than 15%, as well. The higher nitro requires a much greater fuel flow than lower nitro.

Cambo

My Feedback: (2)

are u using a pitts muffler?

RCVFR

My Feedback: (7)

Yes.

Cambo

My Feedback: (2)

very well mite be your problem. Mine did that too with the pitts muffler. Lack of back pressure prevented me from leaning the engine out on the ground. No matter what way i turned the needle it wouldn't change. In the air it would lean out. The slimeline 91fx pitts muffler worked better but i still had problems. The fixes are clogging one of the exhaust outlets or running a pump.

Ed_Moorman

My Feedback: (1)

With a Pitts muffler, the exhaust outlet area is too big so you don't built up enough back pressure to adequately pressurize the tank. You want the total exhaust area to be the same as the stock muffler. You need to either plug up one side or take pliers and squeeze both sides down to reduce the area.

In addition, you might try to stick to a max of 10% nitro fuel.

prgonzalez

Thanks all of you for your input.

1. I already plugged one leg of the pitss miffler.
2. I will do as Turk1 suggested. I will open the LSN so I can see the HSN operational. I was really concerned as playing too much with the LSN because transition from idle to full throttle was okay.
3. I will follow Jim's advice and use 5% nitro.

I will report progress soon...

Pedro

Ernie Misner

Also, the opening in the cowl that the air EXITS needs to be twice as big as where it enters.... or you will overheat!

Ernie