Symptoms:
Engine idles fine with glow starter on, advances fine to mid throttle, remove glow starter and it still runs fine. Tune for high speed, and get a nice rpm. I retard the throttle to look for an idle, and just before the stick is full back, it loads up. As soon as I advance the throttle, it cleans up. You'd think...low speed adjustment. I've gone from 1 turn out to 2 1/2 at quarter turn intervals, and it still loads no matter what. I didn't want to go less than one turn in fear of seizing it. It's mounted inverted in a Model Tech P-51, and the tank level (at the output tubes) is level with the carb, putting the klunk about an inch below that.

Sorry if this is an old repeat question, but I couldn't find exactly what I was looking for in a query of the forums.

Components:
Magnum XL 61RFS
20/20 YS Powermaster fuel
Thundercat plug

Are you using an idle bar plug ? If you are....try a Fox Miracle
plug or an OS type F plug. Keeping the glow starter on is
the clue....it needs more heat....

Dave.

When you start the engine, how does it idle without the glow voltage on? After the engine warms up, of course.

Also, what prop are you using?

Enjoy,

Jim

It idles great with the plug on. I'm using a 13X6 prop. A few guys have already told me that I might try a better plug that burns a little hotter/better. Probably the solution. I hope.

Thanks!
brushfire2000

A 12-6 is more like the prop to use. With a 13-6 on a hot day, the HS needle will typically be hard to set. Also, you will not get much throttle response above 3/4 open. It should run somewhere between 9600 and 10,400 with a APC 12-6 depending on the engine, fuel, and density altitude.

Enjoy,

Jim

How does it idle WITHOUT the glow plug battery connected, is what I was trying to ask.

I have 5 magnum 4-strokes and all mounted inverted...Am using an OS "F" plug...no idling problems yet..try one of them

Sounds like you are to rich on the low end. When it loads up, you should be turning the needle in, not backing it out. I believe my larger one is 3/4 of a turn. Just as comparison. Lean it until you can idle, then check the transition. Don't be afraid of getting to lean on the low end, your engine will lose speed without loading up, then die, and you will know right away.

brushfire2001,

w8ye is right. Probably has nothing to do with the loading up at idle problem, but with a 13X6 the engine is over propped! You can get away with an APC 12X7 if you have a really clean and fairly light plane, otherwise an APC 12X6 is the right prop.

OS "F" is the best plug I've used on all my Mag 4 strokes.

Gary

I have the same problem with my magnum 80 four stroke runs great right side up, but wont idle well or not at all inverted. Some have suggested putting an on board glow to help remedy the problem. It does idle well if the glow ignitor is on.

Jeff

Sounds like over-rich idle

Brushfire, just to eleminate one of the variables, could you turn the plane over on it's back and see if you can get the engine adjusted to where the idle is right?

Another thing but this is a long shot is that you should start to make your idle evaluation the moment you put the engine at idle. For example, full throttle then bang to idle.

The engine may slow down from that point and maybe quit? too rich

It may speed back up and maybe quit? too lean


Also, has the engine ever idled correctly? There may be something wrong with the idle needle? It maybe too short? it may not even be sgrewing in and out but just turning?

Good luck,

Jim

Is the carb mounted high up on the back of the engines on the
.80's ? It's starting to sound like a fuel problem to me.

If the carb is way below the tank in the inverted position, that
darned "gravity" might be causing the rich condition....

Most four strokes have the carb mounted directly behind the
crankcase.....and which way you mount the engine doesn't
seem to matter....

I have been running an Enya 60-4C with a 13x6 Master Airscrew for nearly twenty years with nary a problem. It runs just fine and is my preferred prop for most models in which I use a four-stroke .60 engine, such as a Goldberg Cub.

A 12x6 or 12x7 is an excellent prop for a .48 - .52 four-stroke. Using them on a .61 is underpropping the .61, although I doubt it will hurt a thing.