YS-120FS Rich Idle
#1
YS-120FS Rich Idle
I picked up a box of bits that were the remains of one of these and figured I could do with a challenge over the stock 2 and 4-strokes I dealt with in the last 3 decades. Only question was which version. Have to admit was a bit lost on that one as there were a few different cranks available.
When I went to put it together found the threaded portion of the crank bent in a spiral, which would make straightening it a chore so posted a request for a match, with the new style piston a bonus if available.
To be honest I was surprised by both the short span before replies, and the number of suggestions and offers. Gotta love this hobby.
Anyway, I was able to locate what I needed to use most of the pieces from the original. In fact, I got a box full of goodies, cases, cranks, bits and pieces, to allow for a second engine to bolt together and still have lots of spares. Hoo Doggy! I think I will stay with the original dished pistons for now just to see how they run.
Was able to fire up both 120's on 15% nitro/ 19% synth and despite the tales of difficult tuning found the first relatively easy to set up. Started no problem and only required 1/4 turn in on the regulator to have it idling smoothly. Slight HS adjustment a bit rich of peak and it ran through the tank no problem.
That's the fun bit. It went dry at high throttle, (went through fuel far quicker than expected) and away flew the prop, lock washer and the Higleys nut I had on for starting. Seems similar to the Saitos. Found everything but the Higleys.
Had quite a lot of oil coming from the front that eventually stopped and I can only assume it was what was in the case when I prelubed during assembly. Also saw bubbles in the line to the carb at low throttle, but that did not seem to accumulate much, nor affect transition. Considering the tank is wire tied to the stand there may be some agitation. The tank holder will be padded and slightly higher to be in line with carbs on standard engines, so may make a difference.
Second engine was more problematic. Still fired up but idle was rich and no adjustment of the regulator had any effect. Still peaked out pretty well and would continue to idle despite this. Another little note was when I pulled the line to defuel the tank held no pressure. After hunting for the Higleys it was getting a bit dark so did not check for bubbles on the carb line.
So, all told they both perform strongly with no surging at any throttle setting, but have to state they are not at all miserly on fuel. Estimate the fuel burn at twice what the Saito 125 sucks up. And, considering what happens at full if the tank empties in flight I can expect to go looking for new bits.
I had the chance to deal with the regulator a few days later; there was no contamination I could see and the diaphragm appears fine. However, found the brass piston would not provide any pressure lift, even with the screw turned in a lot, (pulled it all apart and could find no signs of anything amiss). For some reason it worked fine with one from a spare reg body, even though the lengths seemed identical. I swapped the entire unit and ran it again.Still rich at idle with the regulator having no real effect. I oriented the tank forward as with the first engine, but found the gasket fit better one way than the other. Ports lined up much closer.
Second run had it idling perfectly in tune and it seemed to stay that way until I throttled up and returned. Back idling rich with nothing effective. Even with that it will idle through an entire tank with no hint of quitting.
Both engines are physically identical and do not have the secondary seal behind the front bearing, (both have OS "F" plugs, but wonder if some NIB "R" type I found in an estate sale would function here). You would expect them to tune the same, as well. On that note I pulled the regulator again and even though the diaphragm looks fine and the adjuster has what I expect is normal tension I replaced the diaphragm with a spare, (used but still extremely flexible)
Both engines are using the same check valve and filters and pressurize the tank fine. Had bubbles from the valve cover on the second engine and after sanding on a flat surface it seals much better.
NOTE: There was a rather rough side mount Pitts-style muffler in the first box and nothing at all in the box of spares so I went hunting. Seems the stock exhaust from my Saito 125a's is a direct fit.
Would appreciate the correct manual for these as it would tell me if I am setting these wrong, let me order the right parts and perhaps show if any mismatch from different versions. Everything fit, but perhaps different cranks would affect how they run.
When I went to put it together found the threaded portion of the crank bent in a spiral, which would make straightening it a chore so posted a request for a match, with the new style piston a bonus if available.
To be honest I was surprised by both the short span before replies, and the number of suggestions and offers. Gotta love this hobby.
Anyway, I was able to locate what I needed to use most of the pieces from the original. In fact, I got a box full of goodies, cases, cranks, bits and pieces, to allow for a second engine to bolt together and still have lots of spares. Hoo Doggy! I think I will stay with the original dished pistons for now just to see how they run.
Was able to fire up both 120's on 15% nitro/ 19% synth and despite the tales of difficult tuning found the first relatively easy to set up. Started no problem and only required 1/4 turn in on the regulator to have it idling smoothly. Slight HS adjustment a bit rich of peak and it ran through the tank no problem.
That's the fun bit. It went dry at high throttle, (went through fuel far quicker than expected) and away flew the prop, lock washer and the Higleys nut I had on for starting. Seems similar to the Saitos. Found everything but the Higleys.
Had quite a lot of oil coming from the front that eventually stopped and I can only assume it was what was in the case when I prelubed during assembly. Also saw bubbles in the line to the carb at low throttle, but that did not seem to accumulate much, nor affect transition. Considering the tank is wire tied to the stand there may be some agitation. The tank holder will be padded and slightly higher to be in line with carbs on standard engines, so may make a difference.
Second engine was more problematic. Still fired up but idle was rich and no adjustment of the regulator had any effect. Still peaked out pretty well and would continue to idle despite this. Another little note was when I pulled the line to defuel the tank held no pressure. After hunting for the Higleys it was getting a bit dark so did not check for bubbles on the carb line.
So, all told they both perform strongly with no surging at any throttle setting, but have to state they are not at all miserly on fuel. Estimate the fuel burn at twice what the Saito 125 sucks up. And, considering what happens at full if the tank empties in flight I can expect to go looking for new bits.
I had the chance to deal with the regulator a few days later; there was no contamination I could see and the diaphragm appears fine. However, found the brass piston would not provide any pressure lift, even with the screw turned in a lot, (pulled it all apart and could find no signs of anything amiss). For some reason it worked fine with one from a spare reg body, even though the lengths seemed identical. I swapped the entire unit and ran it again.Still rich at idle with the regulator having no real effect. I oriented the tank forward as with the first engine, but found the gasket fit better one way than the other. Ports lined up much closer.
Second run had it idling perfectly in tune and it seemed to stay that way until I throttled up and returned. Back idling rich with nothing effective. Even with that it will idle through an entire tank with no hint of quitting.
Both engines are physically identical and do not have the secondary seal behind the front bearing, (both have OS "F" plugs, but wonder if some NIB "R" type I found in an estate sale would function here). You would expect them to tune the same, as well. On that note I pulled the regulator again and even though the diaphragm looks fine and the adjuster has what I expect is normal tension I replaced the diaphragm with a spare, (used but still extremely flexible)
Both engines are using the same check valve and filters and pressurize the tank fine. Had bubbles from the valve cover on the second engine and after sanding on a flat surface it seals much better.
NOTE: There was a rather rough side mount Pitts-style muffler in the first box and nothing at all in the box of spares so I went hunting. Seems the stock exhaust from my Saito 125a's is a direct fit.
Would appreciate the correct manual for these as it would tell me if I am setting these wrong, let me order the right parts and perhaps show if any mismatch from different versions. Everything fit, but perhaps different cranks would affect how they run.
#3
I have the manuals now. Also finally received the deliveries of the parts. YS stated the USPS somehow knackered the first order and another was on the way to me. First order then showed up a day or two later.
I have new regulators, gaskets, some internal bits and will go through both the second problematic engine and a third I picked up at a swap meet. That one had a keeper broken and it ate the valve. Had enough in spares to fix it, but found it was the SC version and the internal seal ring was broken. That also came in the order, along with some crank seals and new front bearings. Hopefully that will solve the fuel leaks at the front drive washer.
Going to take my time and get to them next chance I have. In the middle or reorganizing the build room and getting ready for the Holidays, (grandson proofing the room for family visits comes first).
Will
I have new regulators, gaskets, some internal bits and will go through both the second problematic engine and a third I picked up at a swap meet. That one had a keeper broken and it ate the valve. Had enough in spares to fix it, but found it was the SC version and the internal seal ring was broken. That also came in the order, along with some crank seals and new front bearings. Hopefully that will solve the fuel leaks at the front drive washer.
Going to take my time and get to them next chance I have. In the middle or reorganizing the build room and getting ready for the Holidays, (grandson proofing the room for family visits comes first).
Will
#5
I found all mine came out no problem. It may take more heat if locked in place. Again, congealed lube would be my first suspect.
If you intend to discard the liner may opt to use a pair of Channelocks on the top lip and try and turn it while heating the outside of just the cylinder area. I would also strongly recommend only using a heat gun. A torch tends to be too localized and alloy will not really indicate it is reaching the melting point till it starts to sag. Lots of chances to wreck the case.
I find it takes more time than expected to heat these even for bearing removal so be patient.
If you intend to discard the liner may opt to use a pair of Channelocks on the top lip and try and turn it while heating the outside of just the cylinder area. I would also strongly recommend only using a heat gun. A torch tends to be too localized and alloy will not really indicate it is reaching the melting point till it starts to sag. Lots of chances to wreck the case.
I find it takes more time than expected to heat these even for bearing removal so be patient.
#6
Join Date: Dec 2008
Location: , QC, CANADA
Posts: 6
Likes: 0
Received 0 Likes
on
0 Posts
The liner is scored on two sides of cylinder if removed and discarded; will have to buy new one as well as piston and ring Central Hobbies charges 34$ US for shipping kinda of expensive for 3 small itms
#7
You may be able to grip the sleeve enough to turn it without damage. I have done this before. You just need enough force to try and break it free while heating.
If the scoring is too deep replacement may be your only option regardless. However, if the piston shows no damage it should be reusable. Not sure on the ring as they are free to rotate and may not lock in place to wear one particular location.
Can you post a pic of the bore?
If the scoring is too deep replacement may be your only option regardless. However, if the piston shows no damage it should be reusable. Not sure on the ring as they are free to rotate and may not lock in place to wear one particular location.
Can you post a pic of the bore?
#8
My Feedback: (3)
I use a 1/4 thick steel plate and place it in the BBQ with the engine on the plate. Start out at 250 degrees and let everything come up to temp. Welding gloves work really well for handling the engine when its hot. Increase the temp 50 degrees at a time until the sleeve breaks free.
Dennis
Dennis
#10
Senior Member
I bought a bunch of stuff recently and the shipping cost was about 18.50$ to NJ. Don't know what it would be to Canada but you should get the amount at the end of your order, in yen of course. Just ask SiRi to convert for you.
#11
My Feedback: (3)
I have the original SF 1.20 and I have lost track of the number of flights. I have so many flights I have rebuilt it 3 times including piston/ring and liner as well as a newer updated Cylinder Head with the holes in it for pressurizing the intake charge. In fact when parts were no longer available for the SF I used parts from the newer engines so I don't know what you would call it. I also have a newer F1.20 sitting on the shelf and between the two I think I have enough to last me.
I agonized over what I thought was the extremely rich idle/low end but you know what? It never quit or loaded up and always accelerated without hesitation so I just ignore it and it’s worked this way for many years.
Another thing was all the pattern boys were running these things in Hyde Mounts on 20/20 YS fuel and swore any less and the engines would self-destruct. Well mine has been in a simple Dave Brown fiberglass mount all this time. I run mine on 10 and 15 % nitro with 18% oil with no ill effects.
The old 1.20 SF still hauls the old Lazy Ace about the sky with authority and can be seen dragging gliders and the club skydiver up to altitude.
Due to the nature of some of my other engines I have started to buy one fuel only and that is 15% Wildcat at 18% pure synthetic. It fills the bill for all my engines.
Dennis
I agonized over what I thought was the extremely rich idle/low end but you know what? It never quit or loaded up and always accelerated without hesitation so I just ignore it and it’s worked this way for many years.
Another thing was all the pattern boys were running these things in Hyde Mounts on 20/20 YS fuel and swore any less and the engines would self-destruct. Well mine has been in a simple Dave Brown fiberglass mount all this time. I run mine on 10 and 15 % nitro with 18% oil with no ill effects.
The old 1.20 SF still hauls the old Lazy Ace about the sky with authority and can be seen dragging gliders and the club skydiver up to altitude.
Due to the nature of some of my other engines I have started to buy one fuel only and that is 15% Wildcat at 18% pure synthetic. It fills the bill for all my engines.
Dennis