Hello everyone,

I have a OS 52 4 stroke and I am having a problem, maybe someone can help me out with it.

here is what it is doing .....

it is cutting out at half throttle. I can run it at full open but it seems like it is not running at full power. Then when I start to throttle down it is
acting like it is at idle when I am only at half throttle then dies.
here is what I have done so far ...I closed the needle valve then opened it 2 1/2 turns and I also reset the low end per instructions and still it is doing the same thing. I am at a loss what to do next.

thanks in advance,
blindguarden

First, look in the throat and make sure you are getting full throttle and full idle. The throttle arm should just about touch the back of the fins when closed. It is adjustable to the barrel thogh, so make sure that adjustment hasn't slipped. The way I set mine up is to loosen the adjustment so I can just run the throttle to idle and the push the arm a little further, then open and push a little futher then back to idle and this time push the arm to where you want it to end and lock it down.

Once you have the arm and barrel moving correct, fire the enging up and let it warm a bit, the start leaning it out, Very slow adjustments as the 4 stroke takes a bit to catch up to the mix adjustment. Depending on the prop, you should get it to top out at around 10,000 rpm. You need a tach to make the adjustments because you don't want to run it to lean and you will not be able to tell by ear when you have reached maximum. OK you have adjusted the mix for maximum RPM. Now richen it by about three clicks. You should be running at around 9500 RPM. Now you can adjust the idle. Close the throttle to the point where it will just keep running. At this throttle setting, lean the idle screw for maximum RPM. Lower the throttle a little more and tweek the idle screw a bit more. You should end up around 2200 rpm for the low idle for a fairly new motor. Once it is fully broken in, two gallons some say, then you should get down to 2000r rpm idle with good response when you punch it and no stalling when you slam in down.

After each idle adjustment, go back and re-adjust the high speed. The two interact. You want the engine to jump when you hit the throttle. If it blubbers up to speed when you punch it, your idle it to rich, lean it by 1/16th turn and try again. All idle adjustment should be at 1/16 turn at a time.

If you just can't get it right, you may have air leaks on the needle valves and/or on the carb to manifold O ring. This is a problem with the Magnum 52, at least mine. I've seen smearing vasilene on the needle valves and on the carb to manifold joint recomended as a method to find the air leak. I havent tried it, but it sound reasonable. Also, a new set of carb O-rings is a good investment. If this is a fairly new engine, check with HobbyPeople service, they did a warranty tune on mine when I was having problems. They are good people to work with.

Try what I suggested and let us know how you made out.

Don

thanks Don I will give it a try and see what happens ....I do know that the linkage is set right and the carb is opening and closing like it should.
I will let you know how it turns out tomorrow when I give it a try.


thanks,
Blindguarden

The needle valve settings in the manual are just starting points. You can usually get the engine running using them, but it is far from where you want to end up.

By the way, how old/new is this engine?

I've got the 52, 70 and 91 Mag four strokes with a second 91 on the way. My 52 was quarlsome, but the other two are really sweet, right out of the box. I did have to adjust the needle valves on them though. Other than that, they went into duty. The 70 had about three tanks through before I flew it, but the 91 only had one and on it's first flight it ran near perfect. I'm sure I have an air leak on the 52, but while I was chasing it, I stumbled across a almost new, two tanks, O.S. 52 and bought it. That is a sweet running motor also. I would have to think hard now though as to whether to buy another Mag 52 or O.S. 52. I'm not sure the O.S. is worth the difference, but it is a great engine straight out of the box.

Don

Sounds like a bad plug to me. Put an OS F plug in her to rule that out.

Low@slow ....it does have a new OS F plug in it thanks for the suggestion tho.

campgems,

I have done what you had suggested and now I have things running alot better. It now will run at full throttle and will run at idle with out quitting. I set the rpms at 9800 for the high end and set the low end about 2300 rpms.

it is still running a little sluggish when going threw the the transition from low to high. So does that mean that I need to adjust the low end a
little more?

thanks,
Blindguarden

I agree that the best plug is the OS F, but that was eliminated befor the carb was replaced and then later when I sent the engine in for the "pros" to have a look. I also used four different fuels. Some worked better and some not. None solved the problem. One thing it did though, I have enough fuel now for the next two seasons.

Don

Should smooth out with more run time.