I've been using a Magnum 70 fs for a couple years not. The carb on this engine is different that the other Magnum or OS four strokes I have. The idle jet screws out to a stop vs in to a stop. Getting the idle jet out of whack really screws up the top end. When things don't seem to be adjusting right, start from the begining.

First, buy a tach. You can't adjust a four stroke without one, at least until you have flown the engine for a few gallons and are fimiliar with it's settings. That knowledge doesn't transfer to another engine either. You really need a tach to set up the engine and to keep it set.

All of the four strokes I have, have a very narrow peak. IE lean the high for peak RPM and just one click or two leaner will result in the stalled engine. Adjustments on the highspeed needle should be made 1 click at a time and a count of five at a minimum between clicks. The low speed should be adjusted in icrements of 1/16th turn, and remove the screw driver after each turn. Again wait for a count of five at a minimum before the next adjustment.

To tune this engine, start with the instuctions in the manual for the starting needle settings. Don't adjust the idle from this point until you have made the inital high speed adjustment.

From the manual inital settings, using a tach, start the engine and let it warm up for a miute or so at mid throttle. Go to full throttle and check the RPM/s Start going lean, 1 click at a time and check the RPM's . When you have reached your maximum, go back to the rich side for a 500 RPM drop. ( after a couple gallons of fuel through this engine, this rich drop can be reduced to 300 RPM)

After you have found your high speed spot, the set the throttle for the slowest speed you can and still keep the engine running. Without changing this throttle setting, start leaning out the low speed 1/16 turn at a time for maximum RPM.

Go back and adjust the high speed again.

Go back to the idle and again set for the slowes RPM that you can get and keep running and again adjust the idle for max rpm again. At this point, the engine should idle between 2000 and 2200 and be able to hold this idle for a minute or longer without loading up.

Now, do the final tweek for transistion. Run the engine up to full RPM for a cound of 10 or so and then cut it back to full idle. Let it idle for a count of 10 or so and punch full throttle. Don't go up slowly, but as fast as you can move the stick. The engine should jump to life now without heasiation. If the engine sputters before gaining RPM the idle is to rich and you need to adjust 1 16th turn lean until it jumps with heasitation. If the engine dies as soon as you punch it, the idle is to lean. Go rich by 1/16th turn until it jumps.

Once you have the engine at this point, you will seldom need to adjust the needles. A change in temp and/or humidity may require one click. A change in fuel may require one or two clicks. Generaly speaking, you shouldn't need to make adjustments.

I'm not sure about the fuel you are using. I use the Omega 15%. It has a blend of castor and synthetic oils and a total oil of 17 or 18%. Your fuel should be the same mix. The magnums recomend a castor only or castor/synthectic oil mix around the 17% to 18% range.

As far as the oil on the side of your plane, while it will be a lot less than from a 2 stroke, you will still have the oil. You can route the exhause for a minimum of oil, but I've never seen a plane that didn't have some.

A four stroke swings a bigger prop than a two stroke. I run 12x6 zinger wood or 12 1/4 x 3 3/4 Wide APC composites on my Mag and OS 52 four strokes. They will both spin either of these props near 10,000 RPM. You 70 should spin a 13x6 or 14x4W near the same RPM. I wouldn't think of using a 11" unless it was around 9 pitch. Even the 14x4 is a bit under propped in my mind, but I love the way it pulls.

Make sure you are using and O.S type F plug.

Make sure your tank and lines are good. Any sign of air in the line will cause engine problems. ANY. Even the little fine ones. There should be no evidence of air, even the little bubble that stay at the carb nipple. It is getting fed from air further back. I've found it best when chasing down this problem to pull the tank and replace all of the tubing from the clunk forward with fresh tubing. Do it once and do it right and you won't have trouble for many gallons. On the fuel tank issue, if you have an ARF supplied tank, replace it with a Dubro or Sulivan tank. I've seen to many of the ARF tanks split at the seam.

Get a tach and adjust your engine and enjoy it. It is one of the best in the fleet.

Don