Halogen

I have an OS 1.20 surpass III pumped and I just cant get her to idle properly.

I tried leaning the idle mixture screw but if i lean too much it doesnt pick up when increasing the throttle. Then if I slightly richen it to get a proper pick up, the engine is too rich and dies after a few seconds. If I leave the glow on it doesnt die.

I have tried the above by using REALLY TINYmovements of the idle mixture screw and this is not my first time I have set up a four stroke or any other engine for that matter. I have also finely tuned themain idle mixture screw to a point where its nearly lean and I dont get any more increase in revs

Its like the pump is pushing too much fuel in. Could it bethat peace in the carb rotor, into which the idle mixture needle goes into, is damaged or widened ?

Any one had this problem with such an engine ?

PS carb body and regulator are brand new.

Cheers

Halogen

After reading and reading these forums and taking Bax s advice on how to properly tune these engines , this morning Itried again but I still cant set the idle properly

Its like this:

1. High end needle is exact , a little more anti clockwise revs drop a lot at full throttle and nearly dies.

2. Idle needle a little more anit-clockwise pick-up hesitates

If I leave glow plug on it will idle for ever at really low rpms on these settings, and to me it just shows idle is still too rich.

Help somebody pleaese !!

JRO

Did you try a new plug? I found if I have to leave my glow drive on to keep my engine running that a new plug helps. My OS Surpass 120 111 does best with the OS F plug. Even though the plug looks good it can be deceiving

Halogen

yes I have tried a brand new Fplug. When I did put in a brand new plug it ran perfect for a few minutes and then same symptoms of a rich engine again. I have also tried new fuel whichis 10% nitro and is Model Techniques contest 10.

Im tempted to use an onbaord glow driver but at the same time I dont think I should with an OS engine. The carb casing is new and hence so is the regulator. But the carb rotor which has the "female " bit ,into which the idle mixture assemly goes into, is not and I got a feeling its this that is causing the mixture to remain rich.

I wastold that the carb rotor is discontinued and sothe other option would be to buy a complete carb which is arround 89 dollars .

Realy dont know what else Icould do.

Bax

My Feedback: (11)

First off, the idle adjustment must be too rich. Then start the engine at part throttle. Advance to full and get it leaned properly. You lean a pumped engine as much as possible without detonation or RPMdrop. Then, you can reduce the throttle to find the idle. You wouldthen work on finding the idle mixture and RPM level that work. If theengine just cannot become lean enough to idle, you likely have aproblem with the regulator that's part of the carburetor body. See your service center for assistance with that. The regulator is notable to be serviced in the field.

You may wish to work with your engine on a test fixture, mounted upright. If it will work properly there, then there's nothing wrong with the engine. The difficulty will be in the engine/airframe/fuel system combination.

Halogen

Thanks Bax for the reply but I have done all that exactly how you have described above and I have also read your other post on the subject.

Top end is leaned to the extent that if i contue revs drop. Then lower end needle is turned anti clockwise to the extent that engine cuts if throttle is increased.

Also regulator is brand new, I have just changed carb body including reg few days ago in hope to solve this issue.

Halogen

I had given up on this engine and here I am again after more than 8 months trying to see why I can t get this engine to idle properly.

Bax I have done exactly what you said about the settings. BUT Its STILL running so rich on idle.!!! If I close idle mixture more, engine heistates when increasing throttle. Top end is leaned so much that rpms are lower than what it should be at full throttle i.e it is lean at top end ( regulator is brand new after replacing carb casing)

This engine has been a mystery every since I brought it. I m not sure if its yet been run it completly or not. All looks brand new including the mufler. But not sure about compression here...... there seems to me hardly any ! I can easily turn the prop with only a tiny bit of resistance....my saitos have so much more compression . Is this the way it should be ? or have the rings gone after the previous owner had it for years lying in a box ?

Bax

My Feedback: (11)

If you have little or no compression when cold, then your engine may not have enough compression once it's warmed up...you can only get so much improvement when the engine's running. You should be able to have good compression when you briskly flip the engine through the normal compression stroke. If not, then you would start there.

If an engine has been sitting for a long time without use, compression can be lost due to corroded rings, a ring taking a "set" from never being used...it will lose its "spring" and not make a good seal, or bad valves. Valves can also corrode and not seal.

The sources can be quite a few, and all need to be inspected. A good tear-down and cleaning would be one place to start. We'd also suggest that the piston ring be replaced, at the minimum.

Halogen

Thanks Bax for your reply. I have inspected the valves and they do seat properly. Tried pouring alcohol on combustion chamber and there are no leaks. valve clearance are perfect too.All internal parts look absolutely mint condition.

Combustion when prop is turned does not hold at all so I will try changing ring and see from there. Just engines said they need to order it directly from OS and that can take weeks if not months .

Do you sell them Bax ?

Halogen

I have just re inspected the engine. Turning the prop clockwise compression does not hold, but turning prop anti clockwise there is compression and it does hold ! I suppose this is due to the valve timing and is normal .

Very silly of me not to notice this !

Bax

My Feedback: (11)

Turning an engine counter-clockwise will give you more of a compression feel because the parts are lining up in the same direction as when the engine is running. However, if you cannot get sufficient compression when flipping in the normal direction, it may indicate a problem.

If you can prime the engine with moel fuel, you may be able to get it running at a higher throttle setting than idle. Try starting at 1/4-1/2 throttle to if you can get it going. Perhaps the use of a starter will help. If all else fails, you can try starting at full throttle...that's done with control-line engines, and won't hurt your engine one bit, as long as the mixture's on the rich side.

Halogen

I do not have any problems starting the engine. One of my concerns was that the engines' poor idling was associated to low compression, but I now know that this engines compression is normal i.e. low compression clockwise and good compression counter-clockwise.

I just cant find out why this damn engine cant idle properly ! its too too too rich at idle , no matter what you do ! If you lean it further it will die on acceleration. Top end needle is leaned that its just below max rpm.

The only thing that I found, is that it had a 91surpass carb. I have changed the housing to a 1.20 carb but internals are still that of the 91.

. valve clearance perfect (valves tested to check if they seat properly )
. compression good
. engine in and out is perfectly clean so , no sign of abbuse
. needles set according to your advice Bax
. new F plugs used
. new carb body hence new regulator

maybe ............. needs running in ? ( I bought engine 2nd hand so dont know how much it has had )
..........................change fuel ? ( I tried new batch of same fuel 10% nitro , maybe different brand? )


never ever in 25 years have I had such an engine which has given me soooooooooooo much grief ! HAIL SAITO !!!!

RC4LIFE

I too have an OS 1.20 Surpass III.... I can never seem to get it run correctly, even following the OS tuning instructions for a Pumped engine...

RC4LIFE

Question: Of those folks who have had success with this engine (OS 1.20 Surpass III).... where do you have your High Speed and Low Speed needles set? Perhaps I should start at that point and tweak as necessary. PS. My OS is in a Sig 1/4 cub... inverted. Thanks in advance

Halogen

My High end needle was set to approx 1 1/4 but cant remember low end. I have given up on this engine and I had to use an onboard glow to keep idle.

Believe me I have tried and tried. I have had many many engines in my life so its not as if I have never set an engine before.

Its so silly that I had to adopt an onboard glow to obtain a decent idle. Dont expect to get this grief from an engine which costs an arm and a leg !

Run my Saito 125 yesterday and its so sweet !!! Never again will I buy an OS in my life again !

Bax

My Feedback: (11)

If the engine won't run right, then something's wrong somewhere. Of course, the most common difficulty is that the modeler just doesn't get it set correctly or they're using contaminated fuel.

In your case, since it's a second-hand engine, it may have something else going on. It's very possible that it needs a new piston ring. If the compression is low to non-existent when you flip the propeller in the normal direction, then we'd suspect that a lot. You do need to have good compression, even in the forward direction. The main clue is that the engine will run at full throttle, but have a bad idle.

For Halogen: Inverted running will cause difficulties with idle and acceleration for many engines. The key is to have the engine well broken-in when upright, and then put it into the inverted installation after it's been thoroughly-broken in and trusted. New engines need the upright running first. That's only because you can easily get the engine properly adjusted. Start out with the factory's suggested settings and go from there.

ckn

I want to report one of my experience. Two years ago I had an OS FS 91S II P which I overhauled and replaced bearings. After re-assembling I found the engine has serious lack of power and will not improve by tuning the needles. I also found a very strange feeling of compression unlike before. That is, the engine seems to have better compression by turning the wrong way (clockwise). The compression was poor when turning the right way (anticlockwise). After reopening the engine I finally noticed that the cam was misalign by one tooth. After realignment the engine became normal. Halogen you might try checking the cam alignment in case the engine had been opened before.

CKN