I have a OS Surpass ii with pump and the engine runs well , good power and transitions well. I am using a 16x8 prop. I have set the high speed 300 rpm less than peak. Then I set the low speed needle. The problem is I can not get the engine to idle low enough so the plane isn't at a fast taxi. I can get it to about 2250 RPM and will idle there reliably for about 30 seconds maximum and is running rough. then quits. If I lean the idle mixture more it wont idle. If I richen up the idle mixture it will not idle as low. I have little experience with 4 strokes so any comments would be helpful.

I see other 4 strokes idle low enough what am I doing wrong?? What is the lowest reliable RPM I can expect at idle with this engine?

hi ,
i think th 2250 are a very good idle.dont try further. the engine is inverted?

Hi, It is mounted sideways. What I do not understand is that I see other people with four strokes at an idle and the plane doesn't move. My idle yields a very fast taxi.

Please make sure your FS-120 Surpass II engine is set correctly. Once you get a reliable idle, transition, and top-end, if your model still rolls when the engine is running slowly, then you'll have to either add brakes, use softer tires, snug wheel collars to stiffen the rolling of the wheels, or a flatter-pitch propeller. You may have too much engine for the airplane, too, since idle power is enough to make it roll away.

Most people get the high-speed needle set too rich. Here's how to set it:

Your O.S. Max engine with pump should be set up in a slightly different manner than a non-pumped engine. Most modelers tend to get them set with the mixture too rich.

One sign your engine's not adjusted correctly would be surging at full throttle. This almost always means it's too rich. Also, the idle may be too rich no matter what you do to the idle mixture. If the idle is leaned a lot, but it's still too rich, the high-speed needle's too rich and needs to be properly set.

To get a good setting, you need to use a tachometer. Once the engine's had enough running to accept being leaned to peak RPM, use the tachometer to lean the engine to its peak.

At full throttle, lean the engine until the RPM stops increasing. Continue to lean the engine to the first sign of RPM drop or detonation. When you get to that point, richen to the point just before you had the RPM drop or detonation and leave the needle there. DO NOT lean to peak and then richen your usual 1/4-1/2 turn.

With a good-quality fuel, the pump system will insure that the engine receives enough fuel. The regulator in the system will make sure that the mixture stays correct as you change the throttle positions. Fly the engine to see how the mixture may change as the engine unloads in the air. You may have to lean or richen slightly, depending upon how it acts. Once you've found the proper setting, you should note the change from the absolute maximum lean position. Now you have a repeatable setting for your engine.

Newer O.S. engines with pumps have a broader range for the needle setting, but you can use the same method for all of them.

Thank you for the reply. What would a reasonable idle speed range. I will lean according to your instructions. I will also try going to a lower pitch and softer tires if needed.

Any idle between 2,200-2,400 or lower, with good transition to high or from high, would be considered good.

Well switching to a 16x6 made the taxi speed / idle perfect. Engine runs great. Now however, there is a definite decrease in flying performance. Would you reccomend a 14 x10 0r 11 like the manual says for sport planes. This is a sig cap 231ex. It would be nice to taxi well and have good performance.

I have a surpass II that I put back into service after a 10+ year respite. Prior to the respite it ran fine, idles great. Three years ago I started to run it again and the main bearing went bad by the end of the summer. It ran fine on the new bearing for all of last year, but on the first flight of this year it had the bad bearing sound again. The front bearing was still good, but that back bearing had a definite ketch each time around. I replaced it but the bearing noise did not go away. During all this the pump quite and I replaced it with a Perry vp-20 which worked great, then the diaphragm in the carb.. so when I switched to the std goose neck and std carb. I lost a tone of power.

I readjusted the valve lash and flew twice this weekend and a lot of the power was back but the bearing noise was worse too. When I set the rocker arm gap I set it to less than 1 mil.. I normally push it till I’m getting feed back from the springs then back it off till it can feel the slop in the rocker arm as I force it back and forth on the valve and back to the pushrod. The case being aluminum should allow for plenty of favorable CTE mismatch. So that being the case when I did the check of the gaps before readjusting I had 10mils on the intake and just under 6 on the exhaust. This did not strike me at first because the engine had been torn down twice in recent history. But the more I thought about it, I was initially of the opinion I had a bent rod. The more I began to think what ever has changed had to be in the cam train because the gap should not have changed that much without the adjustment device loosening up completely, and I still have that bearing sound. So tonight I plan to remove the cam bearings (I’ve done 5x 4 cycle bearing changes without ever doing a cam bearing shange). Any words of wisdom on how to remove them? should I heat the case? Does it sound like I’m on the right path?

I have not tached the engine lately but would say the rpms are over 3k at idle. Idle is very rough, bouncing the engine all over, and it is hard mounted.

Any thoughts

Joe