Engine Help.
 

Ok, I'm confused. I have a OS .46fx spinning a apc 12x4, and the engine is giving me fits. I got the transition pretty good, but now, whenever I go from full throttle to idle the engine cuts out. I'm really confused about the cause. And my instructor at the club seems pretty confused about what's going on with this engine too. Anyone out there have any tips. I have the idle set at around 3000ish rpm.
Thanks
-john

RE: Engine Help.
 

WAY TOO much prop. Loading up the motor too much.

Try something in the 10-6 to 11-5 range.

RE: Engine Help.
 

The manual claims it's ok with a 12x6-7. That should load the engine more. Hmm. I'll try putting the 11x6 back on and see what it does.
-John

RE: Engine Help.
 

Still doing it with the 11x6. It happens when I leave it at wot for about 5 seconds, then cut the throttle back. It will slowly drop in rpms till it dies. If I just quickly flip it up and down it works ok.
-John

RE: Engine Help.
 

Try a new glow plug or check to see if your fuel line filter isn't clogged up.

Won't hurt to try.

Or.......buy a new engine! :)

RE: Engine Help.
 

The low end needle is not set correctly. The low speed needle is where the throttle is connected to inside you'll see a small screw, turn it out to richen it, in to lean it.

After you start it does it sit and idle all day or slowly drop. If it slowly drops it's too rich. If it gains speed then drops then it's too lean

Also, a 12X4 is not too much prop IF the engine is broken in and tuned correctly. I flew one for several hundred flights on a Twist

RE: Engine Help.
 

The idle will idle all day if left alone. If I pinch the fuel line, it stays the same for a second or so then slightly increases pitch... where I let go cause its gonna die next. THe throttle transition from idle to full is good. It's just when I hold it in wot for a few seconds, then go back to idle that it slowly drops of rpm and dies. I just tried changing fuel tanks to see if there was a problem in the tank. No go. I no longer have a fuel filter in it. I took it off 2 weeks ago when I was trying to figure out a problem. 2 instructors have mucked with the mixes to try to get this to go away. It's still cropping up and has me really really confused.
-John

edit
Very annoyiong to, cause 2 weeks ago it was doing this, and finally got it running right. Then today it popped back up again.

Oh I swapped out plugs again too. Did that 2 weeks ago, but didn't solve the problem. I put the original one back in.

RE: Engine Help.
 

I'd look for dirt or an air leak in the high speed needle valve, possibly a damaged needle seat,

RE: Engine Help.
 

The OS Manual setup chart says to increase your idle RPM. You said your is around 3000 though which seems way high anyhow.

How is it to start after it quits? Does it seem like perhaps flooding or leaning out?

If it was mine, first I would mess with the highspeed needle, lean it out more and try, richen it up a bit and try. If that didn't help I would follow the manual for resetting the lowspeed needle. Close the throttle until it is just completely closed, then screw the needle in until it stops and back it out 3/4 from there. That's the factoy preset. After that, start the whole tuning sequence over. May be an idea? I bought a used .46FX that I was having trouble tuning, it was set up for eastern Canada. That's what I did, helped a lot.

Graham

RE: Engine Help.
 

How do I check for a leak in the high speed needle? That will be my next cource of action. Done for tonight, but gonna bring it to the field tomorow if daves around and have him look at it now that I have found out how to actually replicate the problem every time on the ground. That was a new discovery today, but if no go after tomorow I'll start checking into problems in the engine itself. After it quits it fill fire right back up if I open the throttle a touch. I've been messing with the highspeed a bit, and it hasn't seeme'd to help. I'll lean it out till the pitch drops, go back to peak and then richen a bit. I tried it once right at peak. I may try resetting the low speed if I'm not gettin anywhere after next round. But I would think if it was off, I wouldn't be gettin good transitions, and having good pinch test results.
-John

RE: Engine Help.
 

striderjg, the problem you are having is similar to one we had at the field yesterday . The info being given by these other gentlemen is good. So try them. if it still plays up, remove the spray bar from the engine, and carefully look through the bar, as we found a very short , very fine hair in our problem, which was causing the intermittant problem. Once the bar was cleaned out , and checked again , the problem was solved. Hope you get it sorted out and back to enjoying your flying
Bill from down-under

RE: Engine Help.
 

My 91 o.s. 2 stroke did the same thing last weekend. i found a pinhole in my fuel line so i replaced all the lines and put in a new glow plug. try doing that maybe it will help.

RE: Engine Help.
 

I replaced the lines 2 weeks ago, and swapped tanks today.
-John

RE: Engine Help.
 

I'm betting on a air leak at the high speed needle. 2 weeks ago, I was noticing bubbles in the line between the carb and the needle when at wot. I bet that's where the prob is. How do I chekc that?
-John

RE: Engine Help.
 

take the high speed needle all the way out and inspect the little o- ring thats around it and make sure it not torn. try a new glow plug it might help after all that you did.

RE: Engine Help.
 

Bubbles in the line after a high speed run may indicate fuel foaming, which could lean out the engine, causing overheating, and loss of compression. When you reduce throttle, the engine is still too hot, and consequently insufficient compression, and incorrect low speed mixture. Make sure your fuel tank is well padded to reduce vibrations and foaming.

Second theory is the high speed is set too lean. When you adjust the low end, you MUST reset the high speed needle before you check the transition. Thats after every low speed adjustment.

Also, make sure the engine is up to temperature before you check the transition. Run on the stand at WOT for 20-30 seconds, then idle down, run for 30 seconds, then test transition.

The 12x4 is a perfect prop for the OS 46 AX. It should reliably idle at or below 2750 rpm, and peak around 13000 rpm.

Good luck, and keep us posted.

Brad

RE: Engine Help.
 

Bubbles in the line after the needle but not before the needle in the line coming from the tank are a sure sign of three things. The "O" ring on the high speed needle is leaking air (not too common which could be dirt on the ring or needle seat in the housing) or the line between the carb and the needle has a small pin hole in it right at the needle (very common on OS Engines) or the fitting where the line is attached to the high speed needle is loose (also somewhat common on OS Engines) Another thing I have seen not but only one time is the fitting itself was cracked

if you have bubbles in the line from the tank to the needle and then also in the line between the carb and needle then you have a tank issue, this is not likely since you have all new tank lines and a new tank

RE: Engine Help.
 

To check for wear, I read to pull the needle and look for shiny spots showing wear or flattened areas, it should be a sharp cone.

Hope that helps,
Graham

RE: Engine Help.
 

I think I found the problem. I took off the needle valve today. The needle itself had a o-ring, but the o-ring between the the part the needle valve screws into and that screws onto the engine was MISSING!. Lol. No idea how that happend. Now i jsut need to find out how to get one. Hopefully that will fix my woes.
Thanks all
-John

RE: Engine Help.
 

nevermind. I was looking at the wrong exploded parts list. There is no o-ring there on the .46

RE: Engine Help.
 

Just got back from the field. Dave says it's not getting enough compression. Probably ran to lean when I had a crack in the fuel line between carb and needle valve and shot the sleeve piston. Grrr.

RE: Engine Help.
 

Ouch!

On the bright side its a small engine and parts shouldn't be too bad. [&:] At least you solved it hopefully.

Graham

RE: Engine Help.
 

Unfortuantly not the case. Just checked on the sleeve and piston at tower. 68 bucks. Better just to get a new engine. I'm seeing if anyone at my field has one they are looking to unload.
-John

RE: Engine Help.
 

To little compression can easily mean no fuel loaded in the cylinder Which further 'motivates' my theory. My ST 1.40 did this the other day having not run for a while. Simply switch plugs and richen the high and low needles some. You may have already tried this, but it's worth it to try again if it saves you a new engine. If the engine is being spooled very fast and just ups and dies it's lean. If it stutters then dies, rich. Also, my ST tends to not catch every once and a while. And if I very slowly advance the throttle I can find where it sags, leave it there for a bit and see if it eventually catches, if not richen the mixture..


Cheers:D

RE: Engine Help.
 

nah, we even tried covering the carb, flipping upside down and loading up the cylinder with fuel. The compression was still weak. As for your theory, I don't see a post from ya. What was it? We tried running it real rich, both on high end, and low end. Low end richen'd to the point where the transition started getting guttery. High end with a very noticable drop in rpm from peak. Didn't help. WE also pulled the plug and tested the compression with finger over plug hole. Dave said was way to little, and took of the head. There was atleast one score we could see, and some strange golden color lines running down the side. I asume that was where the nickle from the liner had flaked of revealing the brass interiour. Pretty sure it's a shot sleave at this point.
-John

RE: Engine Help.
 

Ouch. Sounds like you're another victim of the famous OS peeling liner problem. My OS 40FX did the same thing. Not much you can do except replace the engine. A new liner and piston is not economical.

A TT Pro 46 is equivalent to the 46FX, has an excellent reputation, and will only set you back about $80.