Tuning problems
 

I have an old Magnum 40 - bought from a guy getting out of the hobby. I could not get the motor started the first time I tried, then I reset it to factory settings, and got her up an running. While it is running, it seems like it runs pretty rough. For a while it would not run well with out the glow starter attached to it, then after running a bit, and tuning it started to run with out the starter, again, very rough. I found it tough to keep the engine running for a longer period of time, nor could I really get it tuned in well.

I am wondering if I am just used to my OS 46 FX which runs about as well as any motor out there and tunes really well. Could it be I need a newer glow plug?

It seems like it wants to run well, but I am just not able to find the right settings. It could also be that it is still cool up here in the North (about 0 C today when I ran the engine).

Any thought woudl be welcome.

manks

RE: Tuning problems
 

Engines run well in those temps so that shouldn't be a problem.

Symptoms sound like tuning or a plug. Plug change is quick and cheap.

RE: Tuning problems
 

The plug is my first thought as well. I have a couple of spares so it will not cost me anything really. I am hoping that the motor will be reliable, as I would like to drop it into another plane I have built and am waiting to fly. I may put it into a GP Corsair or a Cub if I can get it running right. It did seem to improve after a ran it for a few minutes so I am hopeful with a new plug and a bit more tuning work it will really come to life.

RE: Tuning problems
 

Yup, you need to keep at the tuning.

Pay particular attention to performing the pinch tests at high and low throttle.

Also do all tuning with only 1/3 of a tank of fuel. This is rather important.

Finally don't forget the 60 second nose up test, and the 60 second nose down test.

Once you have all of these dialed in, the engine will be very reliable.

Like most non OS engines, the Magnums just need a bit more TLC to get the tuning right initially, but once set they run very well.

RE: Tuning problems
 

I spent some more time with it late yesterday, it did get much better, it seemed to improve as I ran some more fuel through it. I am still having some problems with tuning it at low throttle setting, but it seems fine at higher settings. I will keep on tinkering with it, but at this point it seems ok to fly with right now, I ran a full tank with no problems yesterday and will do the nose up and down testing later this week. I feel pretty good about the engine overall. I still like my OS motors better!

manks

RE: Tuning problems
 

What is a pinch test? And explain please why the 1/3 tank of fuel?

RE: Tuning problems
 

What is the pinch test? And please explain why tuning is done with 1/3 tank and why it's important. Thanks!

RE: Tuning problems
 

Pinch test:

It's discussed elsewhere, but let me try to restate it.

The pinch test permits you to see if the engine is running too rich or lean.

You are supposed to tune the engine as indicated then while running it at low throttle PINCH off the fuel line leading to the engine.

The engine should speed up and run for 2-3 seconds then die.

If it continues to run longer the engine is too rich.

If it dies quickly without speeding up just a bit, it is too lean.

The pinch test should also be done at high throttle.

---

1/3 tank rule.

Engines lean out as the tank empties.

So it is best to test with everything in a "worst case".

e.g. 1/3 of a tank (or less) and then do both the pinch test and the nose up/down test.

You want the plane dying on the ground with any problems so you can fix them, not in the air...

RE: Tuning problems
 

I hope your Magnum 40 works out better than my .46 did. I bought that thing 15 years ago to save $20 and never could get it to run properly. I exhausted my ingenuity then, came back 12 years later with 2 engineering degrees and still couldn't get it to run well. Frustrated every expert at the field one day with it.

I'm chalking my trouble up to a faulty/porous casting or a cracked something or another that I cannot see. I spent $114 on an OS 46 AX and have not looked back.

Best of luck, but sometimes they are just bad.

N

RE: Tuning problems
 

I got my engine with a package of other stuff (Trainer, radio, New OS 91 four stroke, field box, starter, 12 V, and a 60% built Norseman) for $200 CDN from a guy getting out of the hobby. I plan to use the trainer and Magnum engine as a backup incase I kill my trainer (which has an awesome OS .46 FX). The Magnum seemed to be running pretty well the last time I had it up and running, and based on the feed back from the guy I got it from, it was a pretty reliable motor for him. I think a new plug and some work tuning and it should be just fine for what I want it for. I may end up moving it into my trainer if I get the courage up to make my GP Corsair a flyer this season.

RE: Tuning problems
 

Sounds like a winner to me. I was willing to give my engine to someone who could make it run. No dice. I have a Perry carb one of the long-timers loaned me but just haven't got around to testing it.

N