Did you read the part where I said that it ran better with the low end screw on the ground?

It doesn't sound like any Swiss Clock I've ever seen.

The idle was very poor, but is now fixed.

I'm running an APC 10x3 prop. I don't recall the plug type, and it may be very well the A3 or #8 that it came with. The fuel I now have is a mix of left over fuel from last year. I'd guess it's about 13% nitro. It's about 60% Wildcat 20% nitro and maybe 40% Cool Power 10% nitro. The lube is probably about 18% Klotz. The plane is a 2 pound 2 ounce 3D plane (Extreme Flight RC Mini 3D). The tank is 4 ounces, I think, and mounted quite poorly. The plane uses a power pod with the tank, throttle servo, and engine all on one tray. The tank is held in with a bead of silicon, and never actually touches the tray, only the silicon does. The tank stopper is perhaps 1.5 to 2 inches from the engine backplate. The fuel line is about 6 inches long (with a small loop to aid in fueling) and the pressure line is about 4 inches long. The tray then hard mounts to the plane. I get some vibration at full power and the occasional bubbles in the fuel line. No bubbles except at full power.


With the drill, I now have the screw visable in the airbleed hole and a fair idle. Before, like I said, I backed out the screw so much that vibration made it fall out. It ran better that way, and then I was prompted to go ahead and drill out the hole pretty big.

It starts good, runs hard, and idles OK, but it's no Swiss Clock. Maybe I just got a bad one...

Frank:

There are many places that Jan and I disagree. Two examples; He doesn't like MAS props, and I don't like running pure synthetic lube. 'Specially in a plain bearing engine like your LA - the synthetic does not have the film strength needed for the crankshaft bearing, it wears out a lot faster using all synthetic oil.

But we agree on your idle, as far as the rpm is concerned. The LA 25 should be able to idle a lot lower, maybe not down to 2K rpm but surely you should be able to get down to 2500, and probably when it is all correct, 2200 rpm.

Since you have bored the barrel out yu may have gone too far, and there's not enough "Land" beside the bore to close the carb when brought to idle. The absolute limit, of course, is having the bore 1/2 of the barrel's circumference, if the hole is bigger... Take the carb off and see if the throat shuts fully. Give it a little thought, you'll see the problem. Might be why your idle wont come down.

And welcome to the world of the cheap hop-up. How big is the bore now? Are you up to 0.2" yet? Ready to try yhr Perry at 0.219? You are now a believer, aren't you?

Bill.

"Since you have bored the barrel out yu may have gone too far, and there's not enough "Land" beside the bore to close the carb when brought to idle. The absolute limit, of course, is having the bore 1/2 of the barrel's circumference, if the hole is bigger... Take the carb off and see if the throat shuts fully. Give it a little thought, you'll see the problem. Might be why your idle wont come down. "

I guess I don't really understand this part. My Carb will close 100% shut as viewed through the top of the carb. Are you saying look at it from the bottom? The idle can go down, it just wants to sputter more than I'm happy with. I can, click at a time, lower it until it shuts off the engine. Tomorrow, I'll force the idle down to the mid to low 2000s and see if I can set the mixture there. All I know about little engines tells me that they sometimes like a little higher idle. My 91s and my 72 I shoot for 2000 even. For my 51, I like anywhere in the mid 2000s. I just figured (assumed) a 25 would be a tad higher.

For sure, my particular 25LA isn't up to par with the way Jan describes them. I never saw a Swiss watch run better with parts on the ground.

My 46LA was really good, but the screw was far enough out to force me to pull the spring oversize. After that, I don't think I messed with it at all.

The only engine that I'd really brag about the consistency of is my YS 91 FZ. Now that's a Swiss watch. Everything else I'm flying gives me the occasional headache, but not my YS.

I hope the LA get's to where it needs to be. This little plane is a blast, but kinda tough to see at three mistakes (or one hovering deadstick) high. I need to trust the engine down on the deck to really appreciate this plane.

OK, I got the 25LA running this morning, and clicked down the trim tab until I was flipping back and forth between 2400 and 2600 rpm. I set the needle to hold as steady as possible. After achieving the sound of a good tune, the engine would transition, again, 100% of the time. The only "problem" was that after more than a minute or so, the engine would start to sound like it was loading up. It was smooth as silk until then. A little jiggle of the left stick, and it always came back, but no jiggle=a "sputtering" flameout. I can't imagine that it's lean, as the pinch test resulted in a slow increase in rpm of about 500 consistently then a sag.

So, now I'm thinking that something else may also be missing. The airbleed hole is slightly larger in height (at about 1/16 inch), and double wide. I drilled it all the way into the carb, being cautious not to touch the needle seat. My carb barrel does seem to close the bore completely, and I can idle down to 2400 or 2600 or completely stop the engine with the trim tab. When the loading up starts (after a minute or so), I see rpm as low as 1900, before I jiggle and recover (or not). The airbleed screw threads are no longer visable in the airbleed hole.

Maybe it just needs some more run time, or maybe this old fuel is farther gone than I would have thought. With the fact that it does transition (2600rpm to 12,800rpm) and that it can be jiggled back from as low as 1900 rpm, I think I'm OK as far as the plug goes.

Unless this brings up some new (or different) thoughts, I think I'll just live with it, and be cautious of an idle below 3,000rpm. At 3,000 I doubt it will roll in our grass anyway. I'll just have to click down the throttle trim when I start to flare and settle in.

Bill, as for your Perry carb, I'm still not sure I can do the turning down. I might be better off trying to open the throat of the crankcase and just use some Permatex to guarantee a seal. Any chance that will work? Also, does the Perry mount the same (a screw from each side) as the LA carb, or will I need to create something?

Thanks again to Bill and Jan for the advice.

Frank:

Pardon the delay in this reploy - I was down with a virus. Had an email come from a known correspondent, but it wasn't really him. THe virus was PE_BAGLE.N and I'm finally up again. Have you ever attempted data recovery from a 150 gigabyte system? Or worse, had to pay for it? Ouch!

The bit on overbore of the carb is when the hole is bigger than the remaining land on the barrel, there's not enough barrel left to close the throttle all the way. If you can shut off with the trim, you aren't there so don't worry about it.

Your idle is still rich, leading to the loading up you're getting. This is shown by the rpm rising when you pinch the line. If you were at optimum, the rpm would hold for a cecond or three, then fall. Or if the rpm falls immediately you are on the lean sode. and you can then turn the screw back in to richen it a bit.

Bill.

PS: Short, I know. I have 97 RCU emails piled up. Sorry. wr.