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Old 12-01-2020, 12:38 PM   #1 (permalink)
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Default OS 55HZ Hyper Special Edition

I am having trouble getting my black OS 55HZ Hyper Special Edition that comes with its own special muffler to start and run. The manual states to start with both needles open 2 turns. But that is way to rich as it floods instantly. I can get it to start with the main needle open about 3/4 turn but then it idles too fast and if I trim throttle for lower idle speed it dies instantly.
I have been flying nitros for 30 years and always easily got the engines started and well tuned, but this one has become a mystery.
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Old 12-01-2020, 01:59 PM   #2 (permalink)
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I expect that you already know that the needle settings in the manual only guarantee that the engine will be too rich so as not to burn up (due to being too lean) the first time you fire it.
There is basically no way any engine will fly with the settings listed in the manual. It seems a lot of people assume the initial settings are for flight and not a starting point.

It seems that all the 3-needle OS carb are still basically a 2 needle system - idle and highspeed. The "medium speed" needle simply trims out the transition from idle to high speed. But, if you left the mid-range needle at its initial setting (2 turns open), the engine would still idle and fly okay as long as the idle and highspeed needles set properly for flight.

The first thing is to set the idle.
Unless the carb is damaged in some way, idling should have nothing to do with the high speed needle.
I leave the idle needle (screw-head) alone and lower keep lowering or raising the throttle percentage to open or close the carb's barrel until the engine idles reliably at its slowest RPM (4k RPM or so). I can do that without problems when the mid-range and highspeed needles are at their initial settings.

Have you done any work to the carb?
Have you over-rotated the idle mixture screw? If you turned it past 90° CW or CCW it may have damaged the idle circuit (check page 19 & 20 of the 55HZ H Hyper manual)

The 40L carb does not have a regulator and relies on muffler pressure. Is there too much pressure coming from the muffler? If you disconnect the muffler pressure line and try to start it, does it make a difference?

From the description, I suspect that the main needle is allowing too much fuel into the carb or there is too much pressure in the tank.
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Old 12-01-2020, 06:51 PM   #3 (permalink)
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Originally Posted by ticedoff8 View Post
I expect that you already know that the needle settings in the manual only guarantee that the engine will be too rich so as not to burn up (due to being too lean) the first time you fire it.
There is basically no way any engine will fly with the settings listed in the manual. It seems a lot of people assume the initial settings are for flight and not a starting point.

It seems that all the 3-needle OS carb are still basically a 2 needle system - idle and highspeed. The "medium speed" needle simply trims out the transition from idle to high speed. But, if you left the mid-range needle at its initial setting (2 turns open), the engine would still idle and fly okay as long as the idle and highspeed needles set properly for flight.

The first thing is to set the idle.
Unless the carb is damaged in some way, idling should have nothing to do with the high speed needle.
I leave the idle needle (screw-head) alone and lower keep lowering or raising the throttle percentage to open or close the carb's barrel until the engine idles reliably at its slowest RPM (4k RPM or so). I can do that without problems when the mid-range and highspeed needles are at their initial settings.

Have you done any work to the carb?
Have you over-rotated the idle mixture screw? If you turned it past 90° CW or CCW it may have damaged the idle circuit (check page 19 & 20 of the 55HZ H Hyper manual)

The 40L carb does not have a regulator and relies on muffler pressure. Is there too much pressure coming from the muffler? If you disconnect the muffler pressure line and try to start it, does it make a difference?

From the description, I suspect that the main needle is allowing too much fuel into the carb or there is too much pressure in the tank.
Yes, I am aware of factory setting being for a very rich running. I had never seen a 2 turn setting on the main with any previous OS. And to start it at a main needle setting of around 3/4 seemed a little extreme.

I got this engine “like new” from someone in some forum a few years ago. On receiving it, I noticed it came with a spare rear bearing so I changed to it. This allowed me to inspect the innards. All looked good with little indication that it had ever been run.

As for the carb, I never took it apart so have assumed it all should be well.

With the main ad mid needles at 2 turns open, and idle screw at factory setting of mid position, it will flood immediately.

I will try again with maybe the main at 1.5 and open the barrel more at idle as you suggest and see what happens.
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Old 12-02-2020, 12:39 AM   #4 (permalink)
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Quote:
With the main ad mid needles at 2 turns open, and idle screw at factory setting of mid position, it will flood immediately.
I'm not sure about "all" OS engines recommending 2 full turns out as the initial setting (starting point), but I know all the OS Engines 3-needle carbs I've used had that recommendation in the manual (91HZ-PSS, 91HZ-R and the 61G carb from the 105HZ-R).
And that's the recommendation for the 55HZ H Hyper in the manual.

So, if the thing instantly flooded with those settings. I would have to assume that something is wrong.
Quote:
I got this engine “like new” from someone in some forum a few years ago. ... ... All looked good with little indication that it had ever been run.
If this is the first time you've tried to use it since you got it, you may have found out the reason they sold it to you.
When you put in the new bearing, you may have taken the 40L carb off to make it easier to work with. Typically, you have to do that. But you may want to go one step further and pull out the needle seat for the highspeed and see if it is missing any part or mangled.

As I said, the highspeed needle should not effect starting the motor. If is it slobbering rich when the carb's barrel is almost fully closed, there must be a leak someplace or the pressure in the tank is too high.
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Old 12-29-2020, 05:17 AM   #5 (permalink)
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Im pretty sure I know whats going on.

Look at your carb on the needle side. In between the 2 big needles you will see a plate. The screw at the top is your idle adjustment and the bottom is the retaining screw. Take the retaining screw off (carfull, there is a washer between the plate and the carb body for spacing, dont lose it) and slide it out. There is a small plunger in there that needs to be pressed back into the carb body, its probly stuck to the plate side rt now. They come loose somtimes and when It does, it puts the carbs low throttle mix from idle circuit to main circuit. If you look you will see the plunger is keyed into the carb so it only goes in one way. Push the plunger back onto its seat and reassemble the carb. Set your needles to 2turns each and start tuning.

Summer time my os55 runs about 1.25 to 1.5 turn out on main needle. 50 degs and colder im at 2 turns, maybe add a click or two more but either way, im really close to book setting in the winter. The main needle has almost nothing to do with the idle mix screw. If its rich at idle adjust the idle mix screw. Just get it in the ball park, you will fine tune once up to temp and your main is closer.

Hope this helps.
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Old 12-30-2020, 08:11 PM   #6 (permalink)
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Quote:
Originally Posted by Deadpony View Post
Im pretty sure I know whats going on.

Look at your carb on the needle side. In between the 2 big needles you will see a plate. The screw at the top is your idle adjustment and the bottom is the retaining screw. Take the retaining screw off (carfull, there is a washer between the plate and the carb body for spacing, dont lose it) and slide it out. There is a small plunger in there that needs to be pressed back into the carb body, its probly stuck to the plate side rt now. They come loose somtimes and when It does, it puts the carbs low throttle mix from idle circuit to main circuit. If you look you will see the plunger is keyed into the carb so it only goes in one way. Push the plunger back onto its seat and reassemble the carb. Set your needles to 2turns each and start tuning.

Summer time my os55 runs about 1.25 to 1.5 turn out on main needle. 50 degs and colder im at 2 turns, maybe add a click or two more but either way, im really close to book setting in the winter. The main needle has almost nothing to do with the idle mix screw. If its rich at idle adjust the idle mix screw. Just get it in the ball park, you will fine tune once up to temp and your main is closer.

Hope this helps.
Thank you dead pony. I will check that out and give it another try when the weather allows. I had replaced that carb with one from one of my OS 50 Hypers with the Hypers muffler and it worked for a brief test hover in the back yard.
But I really would like to get it working with the original carb and muffler.
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Old 01-06-2021, 02:47 PM   #7 (permalink)
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I'm having exactly the same problem with my .55hz. The plunger Deadpony is describing has stuck on the wrong side and isn't seated where it's supposed to be. However when I assemble everything correctly it keeps coming unseated. I think it's because the little rubber o-ring doesn't fit snugly. Going to soak it in fuel to see if that solves the problem. If not I'll get a new o-ring. Anyone know what size it is?
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Old 01-16-2021, 12:12 AM   #8 (permalink)
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Quote:
Originally Posted by Deadpony View Post
Im pretty sure I know whats going on.

Look at your carb on the needle side. In between the 2 big needles you will see a plate. The screw at the top is your idle adjustment and the bottom is the retaining screw. Take the retaining screw off (carfull, there is a washer between the plate and the carb body for spacing, dont lose it) and slide it out. There is a small plunger in there that needs to be pressed back into the carb body, its probly stuck to the plate side rt now. They come loose somtimes and when It does, it puts the carbs low throttle mix from idle circuit to main circuit. If you look you will see the plunger is keyed into the carb so it only goes in one way. Push the plunger back onto its seat and reassemble the carb. Set your needles to 2turns each and start tuning.

Summer time my os55 runs about 1.25 to 1.5 turn out on main needle. 50 degs and colder im at 2 turns, maybe add a click or two more but either way, im really close to book setting in the winter. The main needle has almost nothing to do with the idle mix screw. If its rich at idle adjust the idle mix screw. Just get it in the ball park, you will fine tune once up to temp and your main is closer.

Hope this helps.
Thank you indeed. I was finally able to do as you suggested and mounted the engine on a test stand. It started right up and after tweaking the main needle for max RPM, and backing off a bit, it ran great and idled down to 1500. Thank you. It will be put back in the heli shortly and tested next when the weather permits.
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Old 01-16-2021, 04:00 AM   #9 (permalink)
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Quote:
Originally Posted by MotorRotor View Post
Thank you indeed. I was finally able to do as you suggested and mounted the engine on a test stand. It started right up and after tweaking the main needle for max RPM, and backing off a bit, it ran great and idled down to 1500. Thank you. It will be put back in the heli shortly and tested next when the weather permits.
Glad I could help.
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Old 02-18-2021, 01:37 PM   #10 (permalink)
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So soaking the o-ring in fuel did work but only for one flight and then the plunger came loose again. I've been searching for the o-ring (os part #27881820) but am coming up empty on my searches. Any one know where to find this tiny little part? Or is the only way to get it is by ordering the carb barrel?
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Old 02-20-2021, 03:37 PM   #11 (permalink)
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Originally Posted by jiminator View Post
So soaking the o-ring in fuel did work but only for one flight and then the plunger came loose again. I've been searching for the o-ring (os part #27881820) but am coming up empty on my searches. Any one know where to find this tiny little part? Or is the only way to get it is by ordering the carb barrel?
As stated earlier. I thought I had fixed mine. But the next time out, it started flooding again. I have now sent it back to OS in Japan. Looking forward to seeing what they come up with.
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Old 02-20-2021, 04:00 PM   #12 (permalink)
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Sorry you guys are having problems. All I can say is its a bit tricky to get that needle to seat. If I didnt get it, the next flight it would flood. Push the needle in and rotate till it drops all the way in. If you can spin it, its not seated all the way.

Hope this helps
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Old 02-25-2021, 01:04 PM   #13 (permalink)
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Yes, I would suggest that you replace that o-ring 4-3, (27881820).
https://www.towerhobbies.com/on/dema...-Manual-EN.pdf
You can get it at Tower, Amain, Ebay, etc..........
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Old 02-28-2021, 12:42 PM   #14 (permalink)
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Funny, I had searched using the part number at both Amain and Tower and could not find the part listed. Checked again at Amain and was able to find it. No matter, it's been ordered and hopefully I'll have it this next week if the mail cooperates.

I pulled another .55 carb apart and the plunger stays in place so I believe the oring ought to solve the problem. When I put the plunger back in I do make sure it clicks into place
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Old 03-10-2021, 12:29 PM   #15 (permalink)
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Received my new part from Amain and re-assembled the carb. Pulled it all apart several times and the plunger would still come unseated. So I took the carb barrel out as well as the plate from the idle side and just tried putting them together and taking them apart. There was some friction between the parts which didn't seem to be normal kind of like a burr. I took a really fine stone and just rolled the plunger on it a bit at a time until things smoothed up. Then re-assembled them into the carb. Now I can pull out the plate without the plunger coming out with it.

Can't test the heli yet as the winter winds have hit the desert for the last 3 days. Don't know why I was able to fly this heli for so long until having this issue. Hopefully this will solve the problem. Will update when the weather cooperates.
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Old 03-10-2021, 01:38 PM   #16 (permalink)
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pretty odd but glad you got it figured out.
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Old 03-10-2021, 05:41 PM   #17 (permalink)
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jiminator
You just did what I was going to suggest next if the new o-ring did not fix your problem.
I use a small piece of 2000 grit wet or dry sandpaper wetted with a light oil. You are best to remove both sides of the carb. The air valve rotor on the throttle side and the fuel mixture valve ("plate") on the needle side. What you and Dead Pony call a ("plunger") I call a fuel valve rotor. It rotates not plunge in operation. It is the second part of the fuel mixture valve. It contains the "Cat eye" which rotates past the rectangle window in the other part of the fuel valve ("plate"). This controls the proper amount of fuel going into air valve rotor and then the engine. This is why it is "keyed" with the pin to the air valve rotor. When dislodged from the pin it can not rotate properly and feed the proper amount of fuel and most times flood the engine with too much fuel. Any drag between the two parts of the fuel valve, "plate" and "fuel rotor" will cause the fuel rotor to "unkey" from the air rotor. It is not because it is trying to "stick" to the "plate".
While both parts of the fuel mixture valve are out of the carb, test how smoothly the two parts rotate together. Remove any burrs, dirt, or dried oil residue by polishing with the oiled fine wet or dry sandpaper.
Reassemble the carb by placing the "plate" back into it's location on the needle side of the carb. Then place the ("plunger") fuel rotor in the air valve rotor, making sure they are properly "keyed" together, then into the carb body. Do not try to replace the fuel rotor ("plunger") from the needle side of the carb. Why? Because you may not get it properly "keyed" into the air rotor and you may make a burr on it trying. Then you would have to start all over.
I found this normally solve the problem if a new o-ring does not and sometimes a new o-ring is not needed.
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Last edited by balsabasher; 03-10-2021 at 05:52 PM..
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Old 03-11-2021, 02:06 PM   #18 (permalink)
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Thanks for a great explanation balsabasher! Thanks also Deadpony for helping isolate the problem. I pulled the engine out when fixing this due to it being way easier to pull and disassemble the carb with the engine out. Looking forward to the first non windy day to try it out. Jim
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Old 03-14-2021, 02:19 PM   #19 (permalink)
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Success Had a nice wind-less day today so I took the lull in weather to try out the fix. Other than having to readjust my needles (had set them to default settings) everything went great. This engine always fires right up so no problems there. It was definitely running rich so I took about 1/2 a turn out of the midrange because it wouldn't transition to the high needle very well. That helped alot. Still have some fine tuning to go but for today got in two nice flights. Think I'm going to pull apart my 1.05 and check it out now that I know what to look for as it is exhibiting some of the same issues as the .55.

All in all a very simple fix once you know what to look for. Thanks to all who have helped in this thread.
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Old 03-15-2021, 01:26 PM   #20 (permalink)
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Great! Happy to help!
I was having the same problems on a Hyper 50 which caused me to look closer and figure it out. So I learned more too!
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