Dave in UAE

I have a Magnum FS 120 on the front of my W of M 120 Ultimate ARF.

As this is my first 4-stroke I have been trying to read as much as possible from the net and follow the manufacturers guidelines. I have not been able to start this engine for the past two days. Today I re-routed all the fuel lines to by-pass the refueler valve to ensure an unrestricted flow to the carb (via a filter). The engine will fire on occasion (so I know the glow plug is working and juice from the battery is not a problem), then it does nothing. When it does manage to start it runs for no more than 5 seconds and dies.

There is plenty of fuel, I've adjusted the needle valve and attempted to start with the recommended 2 1/2 turns of the needle up to a full 3 turns and even at only 2 turns of the needle and nothing seems to work. I understand the larger 4-strokes need to be "wet" to start, but I have done that repeatedly, no hydrolock yet. I went and calmed down for a while and let everything drain and started over again but the results are the same. As a last resort I let everything settle down, applied power to the glow plug, grabbed the starter and tried to get it going, just like I do with my 2-strokes, it fired, ran for a whole 8 seconds and then died.

I reset the mixture to the factory settings and tried but to no avail.

I am going to buy a new baseball bat, hopefully I won't need to give it some Louisville encouragement!, any suggestions, please tell me I am doing something obviously wrong.

Cheers

Dave

MinnFlyer

My Feedback: (4)

Are you using a 4-stroke Glow Plug? (There are Glow Plugs specifically designed for 4-strokes and you MUST use one)

What fuel?

Are you running pressure?

Ram Jet

Thanks Minn, I was not aware that there were two cycle and four cycle glow plugs. Now, how the heck do I know what's in my used engines? I guess I'll have to buy a four stroke plug from the manufacturer to be sure.

Bill

Clay Walters

Dave,

I can imagine your frustration and don't know what the problem is. But I do know if I were there the first thing I'd do is install a brand new Fox Miracle or OS Type F glow plug.

Regards,

Clay

opjose

The Magnums have a fairly TIGHT tuning range.

I've found that on a new engine 3/4 turn takes you from full rich to full lean and anything outside of that results in no starts, just an occasional ignition stroke as youve described.

They really do need long four stroke plugs as stated...

Set the needles to slightly more open then recommended.


- Flip the engine over and make sure that fuel gets into the carb...

- Watch to see if the fuel siphons back into the tank ( it should not, or it should do so very slowly at worst ).

- Then try to start the engine.

- If after 2 to 3 attempts it does not start, lean the LS needle in by 1/4 turn and try again.

Rinse lather and repeat until the engine starts at high idle and then work on the HS needle.

Meesh

My Feedback: (135)

Make sure the low speed needle is open. It affects everything.

Dave in UAE

Thanks guys

I am using an OS F-type plug with Byron 10 % nitro fuel, in fact I went and bought 2 more plugs tonight so I"ll drop a new one in and try the tips you guys passed along.

Cheers

Dave

GhostRider32

Sometimes it's easier to put a new engine on a test stand and run it until you get it tuned.

Dave in UAE

Well I went back to basics (trial and error). Set the HS needle at 3 turns then kept adjusting the low speed needle until it finally started. Ran it very rich for the first 5 minute run and then shut her down, closed the needle a quarter turn for the second run and she ran fine, although rough and smoky but still very rich.

Was 2/3rds through the 3rd run when I completely miscalculated the fuel in the tank. After each run I would add fuel to the tank (keep in mind all my flying has been with .60 size engines and smaller tanks), I use a timed method which works well with my pump and smaller tanks, not so with the bigger tank and bigger engine (idiot!). So after running out of fuel I replenished the tank completely and tried again.

This time no such luck at all and I am back to square one. I primed the lines and actually watched the fuel going into the carb, swung the prop backwards for a turn to drain some of the fuel, applied power to the plug and nothing. SO, I will wait a few days and try again. At least I know it runs, now just have to tweak things a little more.....

I have two test stands, one for smaller engines (won't fit, tried already) and the other for my Clark Merlin which is way too big.

Cheers

Dave

GhostRider32

Glad to hear you got it running. How did it run? Rough, smooth?

LDM

My Feedback: (15)

I do one thing religiouly with magnum 4 strokes every time I fly and it works great . A buddy told me a long time ago that the original designer for OS went to design magnum years ago .While they are great engines , they are not as smooth internaly from the manufacturting process .
ANy way , he said before every start remove the glow plug and put a drop of after run oil in , I swear it works like majic , these engines love oil !!!

ABORH

The advice you are getting is great. I have just a couple of things to add. These engines take for ever to break in. I have .52, .70, and .80 FS Magnum engines and they get very nice after a gallon or two of fuel. In addition it is worthwhile to check the clearance between the rocker arm and the valve stem after about an hour of run time. Especially on a new engine, the clearance can widen as the engine breaks in, resulting in difficult starting and or loss of power. The correct gaps are listed in the instruction book. In the box, you might have even received the little feeler gauges necessary to check this.

w8ye

My Feedback: (16)

The clearance is .04 mm to .1 mm for both valves. That would be .002" to .004"

Dave in UAE

Have been on the road for a couple of days and will get at it tomorrow after a good night sleep tonight.

For GhostRider32

Yeah the engine ran very rough for both runs and most of the short 3rd run, until she started to lean out and "transition" as the fuel ran out, but for the brief second or so she ran quite smooth. Should have shut her down when she started to lean out but was too slow to get it through my thick skull she was out of fuel!

Truly do appreciate all the comments, my Clark Merlin was a piece of cake compared to this one.

Cheers

Dave

opjose

Yeah this is fairly typical.

The manufacturers recommend settings that are overly rich in the hopes that you do not ruin the engine while breaking it in.

The Magnums arrive fairly rich... and once you start leaning them out, things improve... just remember to take it slowly as you are still breaking the engine in.

w8ye

My Feedback: (16)

I have a ASP 120 which is the same engine. I think the main needle runs at 1 turn.

KB9STD

My Feedback: (1)

If it ran lean and quit(when the fuel tank ran empty),it may well have blown the glow plug.

Dave in UAE

Been on the road for a week so will get at it hopefully this week. Tried to get her going before I went away, no luck at all. Will start over with the needles and put a new plug in and see what happens.

Cheers

Dave

maukaonyx

Dave,

I hope this info helps. I was reading my Feb 09 issue of Model Aviation and came across this article in the monthly Engine Shop column...this is on page 92. Read the part that starts in bold letters "My recent mention of starting problems with a couple of Magnum four strokers..." Hope it helps you along. I have seen a couple guys at my club field with the 70 and 91 Magnum four strokers have no problems starting and running theirs. Maybe the 120 is a different animal. Really hope this article helps ya! GOOD LUCK and good flying. Jon

w8ye

My Feedback: (16)

I'll have you know that I own a Magnum 120 and it has always been the easiest to start and tune engine of the 30 or so that I have. It has always been that way right out of the box.

But that doesn't necessarily mean that his is that way.

kingair41

My Feedback: (13)

I have two Magnum 1.20's in my ov-10. Once broken in they are the cats meow. Brand new out of the box and to this day, I alwas start them with an electric starter and put my finger over the exhaust outlet forcing fuel from the tank into the carb. They like to start wet. With an OS f plug they are a very reliable and strong engine. I run all my engines from the Magnum line up, from 2 stroke .61's to .91's, and .91's to 1.80 in 4 strokes. It takes about 3-4 tanks to give them the required run in time so that they are a consistant performer.

w8ye

My Feedback: (16)

This has been my experience with Magnums

LDM

My Feedback: (15)

remember when you remove the glow plug add the after run oil !!!!! I can not stress this enought !!!!!!! they need help , and the help is easy and comes in the form of the aftre run oil , these engines are great with a little tlc

GhostRider32

To each his own but I have never once added after run oil to any Magnum I have, 2 or 4 stroke. I do use fuel with castor in it and remove the fuel line at idle to purge all the methanol from the engine. All of my Magnums run as well as any OS I've ever owned and I've never had a single problem with any of my Magnums.

kingair41

My Feedback: (13)

Early on when I started flying, I used to use auto transmission oil for after run. But in the last 15 or so years I've been building and flying scale to the point that the engine is fully cowled in and access to the engine fuel line is not feasable. So needless to say no after run in these engines. I needed to pull the head, valve cover, and the push rod tubes to fit a new cowl around the engine head, and I was surprised that there was no evidence of rust anywhere. That prompted me to pull the rear cover off and found it to be free of rust also. Just oily residue. I guess I'm just lucky, but if you're able deffinately use the A/R oil for preventive measures.