SK 90-----WOW
 

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.

RE: SK 90-----WOW
 

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

RE: SK 90-----WOW
 

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.

RE: SK 90-----WOW
 

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.

RE: SK 90-----WOW
 

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.

RE: SK 90-----WOW
 

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.

RE: SK 90-----WOW
 

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

RE: SK 90-----WOW
 

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

RE: SK 90-----WOW
 

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).

RE: SK 90-----WOW
 

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.

RE: SK 90-----WOW
 

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

RE: SK 90-----WOW
 

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?

RE: SK 90-----WOW
 

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

RE: SK 90-----WOW
 

I feel sorrier for the SK engines.


Ed Cregger

RE: SK 90-----WOW
 

:D

RE: SK 90-----WOW
 

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

RE: SK 90-----WOW
 

Put a smaller prop on it.

RE: SK 90-----WOW
 

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.

RE: SK 90-----WOW
 

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.

RE: SK 90-----WOW
 

are u using a pitts muffler?

RE: SK 90-----WOW
 

Yes.

RE: SK 90-----WOW
 

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.

RE: SK 90-----WOW
 

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.

RE: SK 90-----WOW
 

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

RE: SK 90-----WOW
 

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

RE: SK 90-----WOW
 

Hi Ernie,

Yes, I checked the opening in the back is about 5 times the inlet. I really do not think the outlet is a problem at this time. I had an OS-61 in this model before and it was working fine. No problems with overheating.

Thanks for the input though.

Due to bad weather, I was not able to test the proposed changes today. The weather forecast says it will be clear skies by Wednesday. I shall see then.

Thanks to everyone providing their knowledge and sharing their experiences.

Pedro

RE: SK 90-----WOW
 

Finally, I was able to get some time to work on the engine at home. I fully opened the throtle and opened the LS needle until I saw a gap of about 1/64 in the needle. Then, I removed the plug I had on one of the pitts outlets. With the dremell, I made some cuts to the outlets to be able to close them and reduce their area about one half. I also removed some material from the cowl over the engine head. (sorry, I could not upload any pictures, don't know why it would not let me).

Temp @ 68-F, prop TF 15x6, fuel 5% Omega.

I put 5% Omega fuel, primmed the engine, put the igniter, and it started on one flip against compression. Rapidly I opened the throttle to get stable RPMs. Then, I opened full throttle and adjusted HS needle. I was able to go rich from 7K+ to 6K+ in one turn of the HSN. I also had big smoke at the exhaust. I then adjusted the RPMs to about 7000. I throttle up and down for a while. Checked the engine temp after five minutes of WOT and I measured 245-F. Let the 12-Oz tank go empty.

After 20-mins break, I put another tank and went for pick RPMs. I got a max of 8400 RPMs. Then, I back out 1/4 of turn of HSN and got 8100 RPM. I checked temp after five minutes of WOT and got 295-F. Put the plane at 90-degrees vertical and the RPMs increased to 8200 and consistent for about one minute. Then, I checked idle. I open throttle to get around 2400-2500 RPMs. Then, tested at 30-sec, one-minute, and two-minute idle transition to WOT. in 30-sec I got just a bit of load-up. At 2-mins, I got just a small hick-up. This time, the color of the oil at the exhaust gases is clear. No more gray oil like at the beginning.

From WOT throttle to idle, the engine goes to about 3000 RPM and slowly goes down to 2400 RPM. Is this a sign of being a bit rich?

So, I believe I am ready for flying again. I hope I can go to the field tomorrow afternoon.

What do you think about this runs?

Do you think that I still need to open LSN a bit more?

Thanks in advance for your input.

Pedro

edited for uploading pics. Didn't work.[:@]

RE: SK 90-----WOW
 

SK engines, even the ringed ones, have a tapered bore. All other ringed RC engines I know of have straight cylinders. Since the SKs are tapered, the Kangke techs told me to never, never run them rich. There is a break-in schedule in the instructions. As I recall, tank 1 is run at a rich 2-cycle, just after it breaks from 4-cycling. Tank 2 you open and close the needle valve from lean to rich every 10-15 seconds. Tank 3 you set at max rpm and back off 4 clicks, then you cycle the rpm from max to idle every 10-15 secs. Tank 4 is a full power run at max less 4 clicks. On tank 5 you set the idle, then run the rest of the tank out. They will also need a gallon or so of rich 2-cycle running in the air. Expect them to get better for 3 gallons. Sort of like a Saito. (At least mine) I have done 3 SK engines this way and all have run great.

I really like the SK carb. Before I go on, I never mess with the factory low end setting until after I run the break-in. Nearly every engine will run in a rich idle at the factory setting.

As I said, I like the SK 90 carb. I bought a Tower .75 and it had a very rich mid range. I could set the low end to idle for a long time, but the mid was terrible. I dropped on an SK 90 carb and the Tower ran perfectly. Tower did send me a new carb which works fine.

A buddy asked me to check his Evo .61 since the carb wouldn't adjust. I tried it on my bench and it must have an O-ring leak or something because it wouldn't hold a low end setting. Just for grins, I dropped the SK 90 carb on it. The throat diameters are the same. Ran perfectly. I am really impressed with the SK 90 carb.

SK 90s are designed for torque and not high rpm. A 14-6 will normally not run well. The transfer ports aren't large enough to pass the needed fuel for high rpm.

Yep, it's got anhedral!

RE: SK 90-----WOW
 

Hi Gonzalez,Yes, your LSN seems a little rich.Though I recommend you to decide what kind adjustments you need by flying repeatedly.It seems alittle overpropped to me.I also recommend you to try lesser props but again the best way is testing on air IMO.

RE: SK 90-----WOW
 

Ed,

The problem I had was the LSN was giving me a lean condition (previous post). When I ran the first tanks, I was not able to make the engine go rich at all even at four and five turns out of the HSN. But, I did followed the break-in procedure even with the weird needle setting. I did not want to touch the LSN and posted my problem. The recommendation was to open the LSN until the HSN was operational. That's what I did. I was able to go rich 2-stroke cycle and the HSN was operational. I never let the engine go into 4-stroking. And, I hope the engine is not damaged by the first lean runs. But, how can I tell?

Also, in the first two flights, I had overheating condition in the first five minutes of flying at 1/2 throttle. So, what I am trying to accomplish are two things: one, make a correct adjustment of the needles; and two, resolve the high temp condition in flight.

Turk1,

Do you think the Top Flight 15x6 is too much prop for it? I believe I am using one of the recommended prop for this engine, am I not? However, Ed indicates a 14x6 will not be a good prop for it. I can't go to an eight because this Giles is not designed for speed as indicated by GP.

Yes, I do have a concern, I think, I am getting low RPMs with this prop at WOT. I was expecting to be between 9K and 10K. But, could it be the fuel I am using is not good? I will be using a new can this afternoon and I will read the max RPMs.

Ed and Turk1, I really appreciate your advice and help you always provide in RCU and I want to thank you both for that on behalf of us being helped. I am happy to continue learning from you.

Pedro

edited for misspelling

RE: SK 90-----WOW
 

Welcome Gonzalez.It is the problem of LSN while testing in Kangke(I dont think they make tests in factory in China) adjusting to good run not for break in so it is not allowing to richen for 4 stroking.I dont use any SK 90 and Ed is doing great job on those engines so I cant say more about props but seemed your revs are low.Recommend you to tighten the head screws and backplate again(with care please).

RE: SK 90-----WOW
 

Turk,

Yesterday, I almost lost my plane. The SK is behaving weird and overheated again. When I realized the overheat, I set for landing but the engine was already very, very unstable and it deadstick at the wrong moment and the plane stalled at about two feet over the runway. Fixing the plane will take me about four hours total.

By the way, I have sent an e-mail to the new service rep for Kangke. After setting HSN for max RPM minus 4-clicks, I set the low speed for good idle and transition, and again at that point, the high speed needle was not operational. I removed the head and inspected the sleeve and piston top. The piston did not have any carbon built up, but the sleeve is not shiny anymore. It has a dark gray mate color in all piston run. The engine still has good compression though.

At this point, I will wait for the answer of Kangke support and I might do one bench run with a TP 14-6 wood prop and whatch for the behavior. At this point I agree with you that the engine might be a little overproped. Maybe is the prop brand design compared to other 15-6 props that have proven to be perfect combination for this engine.

I don't want this engine to become my second nightmare. My first one was one of those XLS-52A which I need to re-tapper the LSN as the cure indicated in another thread. Or, I might try it with the SK-50 carb if it fits.

I will start the break-in of my SK-50. This time, I will use an APC 12-5 prop as everyone else. I am sure I will have good success with this one.

Thanks
Pedro

RE: SK 90-----WOW
 

Once again, it becomes hard to ignore the issues associated with the quality control of low-cost Chinese engines.

My SK90 is a beautiful little engine and runs like a Swiss watch. It was very easy to set up, starts virtually first-flick every time, pulls good revs on large props and is nicely economical on fuel. It's never dead-sticked, never overheated and never given a moment's grief.

Others seem to have not been quite so lucky -- yet they bought the same engine.

Then we have my SK50 which came with a virtually untapped glow-plug hole, swarf in the combustion chamber, a pinch that really was *too* tight (and I've broken in some *very* tight engines before -- including the Norvel 061 Big MIG) and has decidedly lackluster performance, regardless of prop-size.

Others seem to have been far more lucky however, and more than a few SK50 owners rave about their engines.

Ya pays ya money and takes ya chances I guess.

RE: SK 90-----WOW
 

That is a five minute fix, hardly a nightmare;) Just put the needle in your cordless drill and hold a knife sharpener to the end of the needle while spinning it around until you have a taper that seems ok.

Strange as we have never had to do anything to the carb on several XLS 52`s around here

RE: SK 90-----WOW
 

Certainly, it sucks to be another count in the statistic of bad units. But, when we have a good unit, we rejoice.

RE: SK 90-----WOW
 

Have A tiger shark 90 ringed which I believe is the same engine Got from Kange after a couple of tanks of 10% nitro dropped on a diesel head made by A.J. Coholic 15x6 purrs at 9500 good transition
martin

RE: SK 90-----WOW
 

Hi Gonzalez,I want you to check a possible problem which I met once.I have found that whenever I (or servo) play with throttle,LSN was turn slowly by spraybar and after several play LSN would fully block the spray bar.I solved problem by using tghter o rings on LSN.Maybe you have such a problem too.Play throttle manually some time and check the new LSN position which marked before.

RE: SK 90-----WOW
 

Hi Turk,

I called SK engine support and they told me to send it back for inspection/repair. I will keep you posted on their answer in about 2 weeks.

Pedro

RE: SK 90-----WOW
 

Very Nice plane Ed...it has the colors of our National Flag!! Viva Colombia ;)

RE: SK 90-----WOW
 

I and several others had the same problem. Check this out. Remove the carb and look into the throat at wide open. You should be able to see a gap between the fuel tube and the end of the low speed needle. What was happening was, when the low speed needle was screwed in far enough to control the low speed, it did not back out of the feed tube enough causing a restriction at high speed. the cure is simple, Remove the throttle barrel from the carb. Screw the low speed needle out of the barrel - it has to be screwed right into and thru the throttle body. Grind off approx. 1/16 off the end of the needle. Reassemble,
Start the engine and follow the normal needle adjustment procedures. When all set close to right , again check for clearance between the fuel tube and the LS needle. If a gap is not visible, cut a little more off the LS needle Do this until there is a small gap just visible. You will then find that the HS needle will richen properly. The removal of the end of the LS needle will not degrade the LS adjustment as the tip of the needle is not doing anything when the throttle is closed to idle. It is well into the fuel tube.