This is my first adventure with a YS engine and so far I'm liking it but I'm still in the dark on a few things. I've been able to find the instructions for the 120SC model and it helped some but my AC has a fitting at the top of the air box and one below on the backplate that look like they should be connected with fuel tubing right? Well, when i bench ran the engine I had them connected and it seemed that if I pulled the fuel line off at the airbox while idling, the engine went lean, but again, I only tried this at idle. What are these two fittings for at the back of the engine for anyway? Maybe I'm not using them correctly. I've got the whole one-way valve,pressure, fuel, and regulator thing figured out well enough that using WC 20/20 fuel and a Zinger 16x8 that i'm getting a steady top end of 8400rpm and the engine seems happy but I'm not one to go needle happy and try to find the last bit of rpm I can get. I feel the engine is running at normal temps and has good throttle response. My biggest problem, maybe, is just how much vibration this engine has at mid-range down to idle. The prop is balanced perfectly and it would seem that its just too rich but without a low-speed needle, I dont know how to fix it. I have plans of using this engine in an Ace 4-120 Bipe so it will see mid-range speeds most all the time. Maybe the engine wont make a good sport engine because it was designed to be at WOT most of the time in pattern ships and mid and low throttle vibration wasnt a concern. Thanks for any input you guys might have. Mike

Mike,
PM me your email address and I will send you a PDF on the 120AC.
Jimmy Skids

It's been a few years since I had 1.20AC but you are right about those two fittins being connected and there should be a check valve in that line between the airbox and the back plate as well. I'll look around for a diagram on which way the check valve should be insrted into that line.

As for a rich condition in the low to mid range that is taken care of by leaning the regulator.

Flow should be away from the Airchamber. Arrow points towards the Throttle body and fuel tank with regards to both check valves.
Jimmy Skids

read the manual here:

http://www.geistware.com/rcmodeling/files/fz120e.pdf

Wrong model..... he is looking for AC. Anyone that needs a copy PM me and I'll send it. I can't attach the PDF to RCU.
Jimmy Skids

http://www.probuild-uk.co.uk/factsheets/ys_engines.php

here are a few facts from here

Wait for it......wait for it....(BING!) Oh!..I see now! Thanks guys, and thanks for the link krayzc. I'll bet once I get the check valve in the line from the airbox to the backplate, the midrange and idle might lean up and run smooth. Darn thing is, I just received my order from Central Hobbies for the 75* header and only one check valve. Got to get another looks like. Thanks again fellas, Mike.

Mike,
Sent you the PDF this AM. If you need pictures of the 120AC and the plumbing let me know and I'll shoot some shots of my 120AC tonight.
Jim

Let us know how it works out for you. My old 1.20AC was a pretty nice engine once I got the regulator dialed in.

Jim, I received the PDF and thank you for your trouble. That helped answer my questions on the plumbing layout. I'm still trying to wrap my head around the operation of the engine however, and I wont presume to know more about engine design than YS, after all , this engine sold for about $550 in the late 90's so I have to reason it was well worth it, but why is the check valve between the airbox and the backplate there anyway? Looking at some of the other models with the airbox, like the 91 and I think i saw a 110 too, they didn't look to have the same setup as the 120. Is it some simple form of a wastgate so dropping to idle from full throttle doesn't load it up? Well, anyway i'm glad to finally own a YS, and I feel I stole it on ebay. I've been looking to get a 120 for the Bipe project and was looking at buying a good used Saito or O.S. but both in good use condition were selling for $250-$300 and a guy had a BIN on this YS way less than that so I figured there wouldn't be a better opportunity to give one a try. As the engine and I get to know one another, I'll drop by every now and again to ask a question and to let you know what I got figured out. Now, on this Ace 4-120 Bipe I'm starting, I'm looking for moderate speed but max pull on up lines. I most generally use 6* pitch on all my props no matter engine size, I just adjust the dia. to suit the rpm range the engine like to pull best in. It seems to be the best compromise between pulling power on the up lines, over all speed range I'm looking for and best braking on down lines. I'd like to use a MA 18x6 with this plane and engine combo. How well does this engine like to lug a big prop? I'll try a few different dia. in flight but I'm looking for min rpm numbers I should keep the engine above to use its torque most effectively. Right now, I figure no less than 8k but this engine might be happy down to the mid 7's for all I know at this point. Any of you pattern guys play with numbers this low?. Mike

Mike,
I'm a Warbird guy and usually run my AC in the 9's. I did at one time have it down in the 8's with a larger diameter prop and seem to remember that it did not like it for me. If you wind it up with a little less prop I would think that the transition would improve. From what I can remember the 120AC was a limited production motor that was built for high performance. It and the later 120sc were the only two 120's (I believe) that came with the ringed crank. I'm still a newbie with regards to working on the motors, but I have gotten pretty good a tuning one and keeping it running. I've found that they like cool power 100% synthetic fuel. I've run everything from 20/20 to 65/20 with no problems. Due to cost and wear and tear for sport I would think that this motor would run best for you on a 30/20 blend with an OS F or YS 4 plug. Play with props to get the top end just around 9-9.2K with 30% and you should be able to get yours in line..... below are some instructions that should help...........Use the larger props for the 110 for your 120.

APPLIES TO ALL YS 4 STROKE ENGINES EXCEPT 140DZ


FUEL RECOMMENDATION:

YS 20/20. This fuel is made by several different fuel manufacturers. All are suitable. 30% heli fuel also works well for those desiring more power.

GLOW PLUG:

YS #4 or OS Type F.

PROP SIZE RECOMMENDATIONS:

YS 63 11 x 7, 11 x 8, 12 x 6, 12 x 7, 13 x 5, 14 x 4.
YS 91/110 13 x 12, 14 x 10, 14 x 12, 15 x 8, 16 x 6.
YS 140 Sport - 15 x 13, 16 x 12, 17 x 8, 17 x 10.
YS 140DZ 16 x 14, 17 x 12, 18 x 8.
Other prop sizes may be used as long as the engines run in the recommended RPM ranges. In hot weather and break-in of new engines, use the smaller prop sizes to lessen the load on the engine to help it run cooler.

RECOMMENDED RPM RANGES:

YS 63 10,500 to 11,500
YS 91/110 8,800 to 9,800
YS 140 Sport 8,000 to 9,000
YS 140DZ 8,000 to 8,500

WHEN READYING ANY YS 4-STROKE ENGINE (EXCEPT DZ) FOR RUNNING, FOLLOW THESE PROCEDURES:

1. Be sure that the engines has fuel lines connected per the instruction sheet supplied with the engine.

2. Open high-speed needle valve 2 turns.

3. With fuel tank filled completely and the fuel lines connect properly, prime the engine by running it at full throttle with the starter for 5 - 10 seconds. DO NOT CONNECT THE STARTING BATTERY WHILE DOING THIS.

4. Set throttle at 1/4 open. Have a helper hold the airplane if so mounted.

5. Connect starting battery and apply starter. Engine should start immediately. If it does not, check for fuel delivery and make sure the glow plug is operating properly.

6. Upon starting, allow the engine to run at 1/4 throttle for at least 30 seconds.

7. Advance throttle to full and adjust the high-speed needle to a slightly rich full power setting. When set, slowly reduce throttle to a fast idle.

8. Allow the fast idle to continue for a few seconds, then advance the throttle to full. If the transition from low to high is rich, the regulator screw should be turned clockwise. If the transition is lean, turn the screw counter-clockwise to richen. Adjustment should be made 1/4 turn at a time until you are very close then 1/8 turn for fine adjustment. DO THIS ADJUSTMENT WITH THE ENGINE STOPPED FOR SAFETY.

IGNORE THIS STEP SINCE YOU DO NOT HAVE A IDLE ADJUSTMENT.... ALL ADJUSTMENT WILL BE DONE VIA THE REGULATOR.
9. When the transition is set correctly, then reduce the throttle to full idle. If the idle speed slowly rises, screw the idle screw clockwise to richen. If the idle speed slowly drops, open the idle screw to lean. Work 1/8 turn at a time with the idle screw adjustment. Correct idle speed is 2200 to 2400 RPM. At this point the engine should be set correctly. FURTHER ADJUSTMENTS WILL BE REQUIRED AS THE ENGINE BREAKS IN.

Looks like I've got it figured out now. I dug around in my junk box and I found one of those Formost blue and white check valves and installed it between the airbox and backplate with the flow moving to the backplate. It didn't smooth out the midrange or idle but then I discovered that the regulator was screwed in pretty deep into the housing. I opened it up till it was flush with the shoulder of the housing and that help a lot. It was too lean all this time. much of the vibration is gone and I've got a bit of tweaking yet to do but I'm off to work so It will wait till tomorrow, but for now I know I'm going the right way and its running very good as is. Thanks. Mike

Mike,
Get a YS check valve for it. Others cause problems.
Jimmy Skids

roger...

Hot Dog! This motor is great now that I've got it figured out. I decided to knuckle down this weekend and spend some real time working with this engine to figure it out instead of taking 15-30 min stabs at it, like during the week. While the motor was showing some improvement, It still had way more shaking at mid throttle and idle than I was willing to live with, also I could only get a reliable idle at about 2800rpm. I'm using a new OS F plug so I knew I was in the ball park there. After a few mins I realized I hadn't checked the valve to rocker arm gap, it was waaay out...while I was at it I pulled the regulator apart and found plenty of junk. Nothing gritty but what looked to be brownish dried oil that was flaky and floating around in the fresh fuel of the regulator and around the lip seal of the diaphragm. So after cleaning the reg and adjusting the rocker arms, I put the engine back on the stand and it ran even better, but I couldn't get the idle any lower than 2400-2500 and I've read that the idle should be set at 2000. Up to this point I've been using the wood Zinger 16x8 and it pretty light so I thought I give the heavier Master Airscrew Classic 18x6 a try. Man , did the engine ever like this! Top end was 8100 and the idle was 2100, I could get to 2000 with glow heat but not without. The engine was much smoother across the whole rpm range, maybe the effect that the heavy prop has at absorbing the strong power pulses of the engine. The pull the YS has with the 18x6 is incredible! The only thing I need to do now is find either a hotter plug or add auto glow heat once the engine is on the model. Other than a Saito, what other plug is there to try? Mike.

You want to use an OS F or a YS 4 plug, trust me on this. I had inadvertently put a McCoy into one of my 1.40L engines and wound up sending it in for service because it would not tune and I figured the bearings or ring were shot....Richard changed the plug and sent it back to me...problems fixed.

If you want to add a little more prop weight put an APC on the engine. 2100 RPM is still acceptable for idle and you are only using 20% nitro fuel, it would be easier to get reliable lower idle with more nitro.

Another tip on the plug would be to use an exacto blade and gently pull the element down a "tad".

Over all I'm glad to see that the motor is headed in the right direction..... the idle will probably get better with some run time as well. If the motor is still breaking in I would suggest putting it on the plane and "flying" the motor for break in now that you have it close. These motors like to be flown.

Skids

Thanks for the tip guys. Now where can I find a metal engine mount for this engine? OS has theirs and so does Saito. I've still got the metal T mounts from my old H9 Super Cub that I could use if no custom mount is available. My guess would be that a standard nylon mount is not going to cut it hear.

Mike,
I use the GP120 mount with decent success..... I would love to find a hard mount metal one if anyone has a source.
Jimmy Skids

http://www3.towerhobbies.com/cgi-bin...&I=LXATG7&P=ML

Why do you want a metal mount?

The stiffer the mount the better the transfer for speed.
Skids

That would explain the radial mounts on my Jetts and Nelson then. I don't race so good to know that if I decide to down the road.

Here is my Hanger 9 mounts. After looking over Horizon's website I've found them.....http://www.horizonhobby.com/Products...ProdID=HAN2033

Hi guys,
              I have just purchased a  fully <span id="v4-1"><span>rebuilt YS 120 AC 4 Stroke Engine and i am going to fit it in my CMPro Spitfire. I don't have any paperwork  to help on the fuel system, prop size etc so any info that you can send my way would be greatly appreciated. I am also building an exhaust system in the cowl which will have all 12 exhaust ports used. Its a complex job interconnecting it all together and ensuring i don't upset the back pressure. It will be good to see the all the exhaust stacks working. If it works. The model is a 120 size and i have a new OS 120surpass f/s that i was going to use but i feel it would be a little under powered hence the YS120. 
         
             Thanks for any help you can send my way. I am in Far North Queensland Australia.

regards

The gimp  (paul)





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