Hello I put an OS 61 four stroke on my second airplane which is a Sig Four-Star 60 The engine starts easy and and runs great the problem I am having is when on the ground I set the idle so the airplane doesnt move until i throttle up. Then after 10 or 15 min. in the air when I come in for a landing the idle is way to high so I have to kill the engine and land dead stick in order to land it. I have checked the linkage and it is tight this happens ever time I take off any ideas what is going on?

Set your idle after a significant warm-up period, including some time at full throttle.

the valves could be out of adjustment, there could be an air leak in or around the engine/needles that start sucking air after it gets good and warm.

Does it seem to lose power after it's in the air for a few minutes?

Possibly the engine is not up to running temp before take off or may be a little hot (too lean) and this will cause it to idle higher.
Try getting the engine up to a good operating temp and then set the idle again before take off.
EXCAP232

Ok Slightly OT but not quite..

How does the 4* fly with the OS 61 Four Stroke?

I have one that is currently homeless.. I was thinking of building a 4* 40 but if it'll fly on my 61 ok I'll go bigger.

Hello the engine runs great in the air but after a loop it does cut out for a second then runs good it has never dead sticked on its own I will try the warm up thing and give it a try. And as far as the OS 61 powering the four-star 60 it has more then enough power not a fast plane but lots of power for a newbie like my self rolls and loops great and can climb great im running a 11x7 prop but going to try an 12x6 next time I go out

If it's trying to cut out during or after a loop then it is too lean and if you leqve it like that you will ruin it. To properly tune a four stroke you need a tachometer since you cannot hear the engine change rpm

BUT, I just realized something, I was not aware that OS made a 61 sized four stroke. Currently they make a 30, 40, 52, 70, 91 and a 120

Are you sure it's not a two stroke OS61 which they do make

It's easy to tell, there will be a black valve cover on top of the head, it's almost exactly square in shape and is locate right in front of the glow plug. Pictures would really be nice or tell us any marking you see on the engine

If it is indeed a two stroke, then that makes sense--two strokes take a lot longer to spool down than four strokes. You have to back off the throttle much sooner when landing a plane with a two stroke as compared to a four stroke!

2slow,

I do have to disagree ever so slightly with you

I have had multiple OS46AX's in several different planes and they all responded to power up and power down instantly. I currently have an OS108 in my now wrecked Showtime and once I leaned both the low end and high end it spools right down as does my OS160.

The only time I have seen an OS take a while to spool down is it's either really rich on the high end and it needs to burn off the fuel coming back to idle and if the low end it really lean. Just the opposite can also cause this. Lean high end coming into a rich low end, which I am pretty sure is his problem

Also, if he is running an 11X7 prop it's likely he is overrevving it. I know guys that fly that prop on a 46AX and it turns 10,000.

In either case, two or four stroke, he needs to get the engine tuned correctly. It's obviously lean on the high end since it want to shut off on the other side of a loop.


If it's a 61FX 2 stroke OS lists the props as

11x8-10,
12x7-11,
12.5x6-7

On a 4*60, I would be using a 13X6 with an OS61FX

Once he comes back to tell us about the markings on the engine, then we will know for sure and can steer him in the right direction

Hello yes I'm 100% sure it is a OS 61 4 stroke engine

No problem,,
I'm just going on my experience. I have two os 40 LA's and an evolution .46, and five four stroke engines, and all five of my fourstrokes will spool up and down MUCH FASTER than my two strokes, just my experience....

Ok yep it's a 4 stroke and I found it on OS's web site but the manual was not available so I cannot recommend a prop.

I would start by tuning it. You will need a tach.

Start it then take it to full throttle and richen it until it starts to run rough. Now start to slowly lean it out, using the tach, until you get max rpm and turning the needle no longer changes the rpm (do not go past this as you can cause it to detonate and throw the prop so do this from behind the engine). Once you get max rpm, then richen it until you lose roughly 300 -400 rpm and leave it there.

Now bring the engine to idle and let it sit for at least 1 minute, 2 minutes would be better. Then quickly bip the throttle to half way. If the engine stumbles and spits allot of smoke the the low end is too rich. If the engine stumbles and tries to die or starts to detonate without allot of smoke then the low end is too lean and quickly return the throttle to idle. If the engine instantly transition to half throttle then leave the low end alone.

If you have done all of this and still get the same problem then start looking for air leaks from inside the tank out to the carb, including the "O" rings on the needle valves.

Oh yea, also check the valve clearances, they may be in need of adjustment.

If you need the manual, click the link below and follow the directions

http://www.rcuniverse.com/forum/m_2037866/tm.htm

That link also gets you to the OS engine forum, ask Dave if he can recommend a decent prop for that engine, he's pretty good

I used to run the OS .61 four stroke on my 40 Telemaster with a 12x6 prop around 9,600 rpm
Thats about as small as I'd go.. I'm going to try a 13x6 with it on the test bench soon.

My 4-strokers did the same thing. They started out spot-on, then got lean (especially on the idle) after about 10 minutes and would often quit, making a dead-stick landing the norm. I finally figured out that these engines just didn't have the "suck" power to get the fuel into the carb at the same rate after the tank level decreased an inch or two. To compensate, I adjusted the engine to be slightly over-rich with a full tank. It then leaned out and ran perfectly after the tank level dropped. I don't think you get into this problem with a pumped engine. HTH![8D]

I have a question for you guys
I have just bought a brand new os max FS81 alpha , itĀ“s my first four stroke engine, las week I just took it apart, because I am quite curious , and now I canĀ“t get the right timing , how do I have to do it? , does someone have a tip on how to do it? , thereĀ“s no info on the manual regarding this issue, thereĀ“s not even enough info on how to calibrate the valves , I have looked around , but with no success.

Thanks for your help

Peter