Idle problems! Magnum .91 4-stroke
 

Hi,

I traded for a Magnum .91 4-stroke recently at a swap meet. I finally got around to putting it on something. It runs great on the top end and midrange. But, when I try to get it to idle for very long it die's on me. I've tried different plugs. I've taken the carb apart to clean it. I've checked the valves to see that they were set properly. The best idle performance I can get is with a enya #3 plug. I've turned the idle needle to many positions. When you think you about have it, you turn it just a little more and that's too much! Does anybody else have suggestions?

Thanks for looking, Jeff

The Enya #3 plug is a good plug to use. What fuel are you using? Prop? What rpm are you trying to idle it at?

When it dies, and then when you restart it, is it loaded with fuel and needing to get revved up to clean it out?

How long to you try to let the engine idle at? One doesn't really need to have long engine idle times.
I have a couple of .61 four strokes that didn't work right until I used 15% to 20% nitromethane in the glow fuel. Then those engines ran good. Before with 5% nitro glow fuel they didn't idle well at all. usually I don't have problems with low nitro or no nitro glow fuel in my engines, but I have a few that want more nitro in the fuel.

That's what I've read about a lot of engines, but unless they're that grossly under compressed, 5-10% nitro should be more than enough. You'd likely have to increase the idle speed to ~3,000rpm or higher. Smaller props don't carry as much inertia as a bigger diameter props.

What rpms are you getting at low idle? If you are getting about 2000 I would be happy with that. Are you doing the pinch test at idle to check for lean?

many of the Magnum/ASP four strokes don't like to idle as low as a Saito or OS engine. I've only had one that would reliably idle at 2000. Most are greater than 2500 rpm for a consistent idle.

The Magnum 30 four stroke is lucky to idle below 3000.

I'm using Magnum 20% nitro 20% oil. The prop I'm using is a master airscrew 14-6. It will only idle for 5 to 15 seconds. When I restart it after it quits it seems to run fine. I'll rev it up to clear it out a little and go back to idle. If it's a little lean it stops after about 5 or 6 seconds. If it's a little rich it will idle a little longer then load up and die.

What is your idle rpm? It's probably too low. Like w8ye said - a lot of these engines won't idle as low as the higher quality/cost engines. If idle speed isn't the problem, try adding more nitro or a bigger prop.

Hi guys,

I thank you for your questions and suggestions! I haven't checked the rpm at idle. I've been trying to get it to idle to a point where it wouldn't roll away on it's own. If it will do that, it will slow down to land pretty good.

Thanks, Jeff

You should find out what that rpm is. I have a feeling you're gonna have to idle it faster and deal with a moving plane. There's no free lunch.
You could try an idle bar glow plug and more nitro too but I think your problem is still too low rpm at idle.

I have a magnum .91 four stroke, I added an onboard glow system and can switch it on when taking off and landing, this has helped lower my idle rpm

Hi!
Most four-strokes use the OS F plug, not the ENYA 3.
Suitable prop sizes are: 13x8,14x6,15x4.
Best props are: APC ,Graupner Sonic or RAM.

I once removed the idle needle and failed to note where it was at the time prior to removal. Hobby People told me to take the carb off, turn it up side down and see where the low speed needle was. It should be half way across the split where fuel comes out. I set it and it was spot on. Later I had some idle problems and found the gasket between the intake manifold and head was leaking/missing a piece. It amazed me that it ran at all but did so a high speed just fine, but would not idle. So check the gasket between the intake manifold and the head, also check the o-ring between the carb and the intake manifold and make sure it is in place and doing its job. I found the Maggies run just fine on 10% Nitro and I always juice up my fuel with Castor oil to the 20% oil range. They run like a champ.

I am tired of OS being shoved down everyone's throats. Enya 3 plugs perform significantly better in my Enya 4-strokes at HALF the cost. Oh yeah, Enya recommends Enya 3 or Enya 4 plugs in their 4-strokes depending on model. Generalizing "most 4-strokes use OS F plugs" is a bogus statement because they aren't the only plug on the market that works (well) in a 4-stroke. I dare you to try using a Fox idle bar plug in your 4-strokes.

OS anything is a ripoff. I don't like being ripped off so I use anything but OS. It's about time OS is taken off that solid gold pedestal.

I like Merlin plugs myself.

Fox Miracle plugs also work well in four strokes.

I grabbed one of those myself but had better results with the idle bar plug.... A Super Tigre .51 ate the miracle plug during a test run on a 13x4 prop. It was probably too soon for a big prop.

I have no experience with Magnum 4-strokes, but my Saito and Enya 4-strokes have taken a long time to break in and idle well - 2 or 3 gallons of fuel. As they gradually broke in I was able to gradually lean their low end needles for better idle and better transition.

On the other hand, Magnums have a reputation for air leaks and problematic carburetors. I gave up on my Magnum 46XLS 2-stroke. I never could get a reliable idle from it. Hopefully you have a good one.

My Magnum 52 FS needed a gallon before it would idle reliably.

Hi Guys,

Thanks for all your replies and comments! I guess I'm trying to get it to idle to low. I had another magnum .91 before and it would idle reliably. I guess I'm asking to much of this one. I've tried several different types of plugs and low speed needle settings, and I can't get the results I want. I'm using 20% nitro 20% oil which should be good enough. I'll just run my idle a little higher and fly it! Thanks again for all your comments and suggestions!

Jeff

Hi!
I run 5% nitro(15% -20% oil) in both my four-strokes and two strokes and I can assure you that OS F plug is the one to use if you run that low nitro content. Y&S works too.
No lenghty running in is needed in any four or two stroke . They all run reliably and throttle extremely well after just one or two tanks if you just adjust the low speed needle. Aim for around 2200-2500 rpm as idle speed for a most Engines.

You haven't broken in a new Saito, have you?

Ain't it the truth!

My Sanye .52 four-strokes ran much like the old OS .52 Surpass engines that I had. Which happened to be great. Granted, it took a bit of a break-in to get it there. You had to be patient.

My Magnum .30 four-strokes were lucky to stay running at 3,000 rpm, whereas my OS FS-20 four-stroke engine would idle reliably at 2k rpm on 5% nitro fuel.


Ed Cregger

I am and will agree to disagree with you on all points except the idle speed. 2,500-3,000rpm is what Enya recommends for a good idle rpm for their 4-strokes, and Enya #3 glow plugs. I own Enyas so I follow their recommendations.

I am able to get my Magnum 30 FS to idle at 2300 with a Merlin 2010 plug.