Ever since I switched props I can't get it tuned. It will transition great on the ground and in the air it will transition from idle to full throttle quickly with no hesitation. BUT, like maybe 1/2-3/4 throttle,if I leave it there, the engine goes "blum, blum, blumblum, blum". (sorry it it seems stupid but trying to describe the sound). Now when it idles in the air it idles smooth and at full throttle it sounds good. Trail of smoke and oil is reddish-clear. It's just at that certain point it it seems like it's not running at a steady RPM. High,low,high,low real quick. Should it at any point in the throttle be running smooth with no change at all in RPM?

Also, if you run your low idle too low will it damage the engine or will it just die when going verticle? I know if you run the high speed to lean the engine could be damaged, but does the low speed setting have as much of an impact on engine damage?

I'm kinda of a pefectionist so I try to get things dead on all the time. So when it does this and I have no idea what it means it bothers me. AND I'm real paranoid about damaging my engine. I have spent the last two days just screwing around with the low idle screw and it still not right. But like I said, hasn't died in the air, and transitions fine even when going from idle to full real quick. Just makes a noise like it can't decide if it wants to run high or low at that point.

Can't complain though, on my 4th gallon of fuel and my first 2 flights were on the buddy box and after that I have been on my own with no incidents (besides 2 deadsticks). Even if it's windy I have no problem, totally comfortable with it.

I JUST DON"T WANT TO DAMAGE MY ENGINE!!

Ronald,

The OS.46FX is known to be particularly rich in the mid-range.

Even after adjusting the idle needle for spot-on transition from idle, it will be too fat at part throttle settings, will run at a four-cycle there and if you go quickly from a prolonged 1/4-1/2 throttle, down to idle, or to full power, the engine will stutter and often, will die and give you a dead-stick landing opportunity.

It is not rich enough to die at part throttle, but when going anywhere from that setting, do it gradually, not at once.

Your engine will not be damaged, except by too lean a mixture setting.

Take notice; there are two controls to idle, the idle stop screw, which should be screwed out far enough, so the throttle could be closed by the trim lever (or the radio's cut-off switch), but in enough so the throttle drum cannot fall out.

The idle mixture is the small screw inside the middle of the throttle barrel/arm. It controls the fuel curve at idle and mid-range settings.

If the idle mixture is adjusted perfectly in level flight attitude, it will become too lean and will often die, if the plane is lifted nose-up, at idle. In the air it will not happen, since the plane is slowing down, thus reducing the effort to suck fuel.

Would a high tank position exacerbate the problem?

if you can, disconnect or pinch off the fuel line while the engine is at idle until it quits. If the rpm increases before the engine quits, low end is too rich. If rpms go down and quits-too lean. This is a proven method in some of the manuals which I use all the time. Then adjust the low end needle as necessary. I go for a very slight increase myself.

I've got a .46FX that dies like DarZeelon says. I have to go to idle a long ways out to get the plane to slow down for landing, so go-arounds are usually a 50-50 chance of a deadstick. I think I'll run the low needle valve a little leaner and see if that helps. A lot of people have adjusted this engine and it still does about the same thing most of the time.

Mine does the same thing when trying to land. Takes forever to slow down. I usually cut throttle just at my first turn into the runway. Then by the time I make my final turn into the runway it slow enough to put it in. BUT, windy conditions it kinda helps. If I throttle back too early, It is at a crawl by the time it hits the runway and makes it soI have to give it 3 clicks to get it in.

Everybody is describing the exact same problems I'm having to a tee. Glad I at least know my engine is running as it's supposed to. The only thing is I should have left it where it was because it was running strong and reliable. Just did not know if it was normal. I'll have to tweak it again next time I'm down there at the field.

And yes lean it out a little more. Had the same problem but after leaning it out I could throttle up with no problem from idle.,mm

Is there this many problems with 4 strokes or are they easier to dial in?

I will try the pinching to death thing on my OS 46 FX but here are the signs I have been using to tune it - hopefully someone can confirm if these are right:

low end needle - transition up to full rpm quickly. If engine dies 'cleanly' - i.e. rpms just go down and it stops, low end is to lean. If engine splutters and catches as it tries to raise rpms it is too rich. Also, when transitioning back down to idle if the engine takes ages to get to idle rpm's and seems to be idling at high rpm the low end is too rich.

high end needle - I make it as lean as possible while still being able to pass the nose up test. I.e. when you hold the plane vertically up at full throttle it does not die (if anything it slightly increases in rpm).

photoniq

Remember the low-high transition speed is just another guide. It still could be too lean. A rich transistion is obvious with all the hesitation and sputtering.

In your original post you mentioned "since I changed the prop"...what prop are you using?

I was using the original Nexstar prop. But I nicked it and put on a master airscrew. Both are 11x5.

I have to cut the throttle back to idle around the turn from downwind to base, so the planes floats at idle for a long time in order to slow down enough for landings. It stays hot until about halfway down on final before it begins to slow down and float.

When tuning the low end, I wait 20-25 seconds at idle before giving full throttle to check tuning. In the end, before the flutter and crash in a pond, I turned the screw full clockwise and then backed out a turn or turn and a half. I started trying to set the low end from that point and thought I had it dead on, but I had another deadstick on the 3rd or 4th tank of fuel. I see now where I should have leaned it just a little bit more.

My engine does what DarZeelon says when going from half throttle. It would quit then too. I was doing a lot of half throttle flybys when the flutter problem was first noticed, and slow flight was one of the places it happened, so we fixed some things and I was doing a lot of low passes at half throttle before throttling up to fly off.

The Fantasy will fly again. 95% of the damage was to the wing and that will be rebuilt next week.