Thunderhead

I Have ahd problems with it from day 1. Now Ive switched fuels and problem is WAYYYY WORSE!

When I start it up for the first flight of the day everything seems fine, and first flight is uneventful. Then....Second flight Ill be 1/8-1/4 stick throttle and then hit the gas and it stumbles and 90% of the time it will die and dead stick landing here I come. I was using 10-15% Omega fuel, now Im running 25% PowerMaster. Ive got another 46FX and it runs like a dream, but this one is starting to erk me off!
Is it the low end or the high end I need to adjust?

ksechler

What is you installation? Is it cowled. Do you run it right away the second time or allow it to cool?

Thunderhead

The engine is in a Sig Somthin Extra, no its not cowled. As far as a time frame between flights, it doesnt really matter. It could be after 2-4 people fly or it could be a gas and go. the problem is there for the entire rest of the day once it's been ran the first flight. Now I have played with the low and top end and got it to where the transition from low end to high sounds pretty good and I've leaned out the top end till it starts to puke out then back off till it runs real sweet and then back off like anther 1/8 turn from there. Im stumped. I have read that I might need to run the low end all the way in and back out 1 ful turn, run the high end in and back out 2 full turns. This will allow me to have a good starting posistion. But I'd like to know why it's acting like this.

GBR2

My Feedback: (1)

Sounds like an air leak.

Thunderhead

An air leak? Why does it run good on the first flight?

LearjetMech

No heat in it maybe??? Remember, if you adjust the low you gotta adjust the high.
LOW AFFECTS HIGH
High does not affect low!! So after you adjust the high end are you going back to the low end? If so, you'll need to set high speed!

Homebrewer

My Feedback: (8)

Do a search here on rcuniverse.com. There are many postings on how to tune and engine using the pinch test and how to set your low end needle at an optimum point for fine tuning.

Thunderhead

But if low end has good transition and all seems well on first flight, and yes, high sounds correct, then why after it is warmed up (after first flight) does it seem to puke out when I nail the gas after a period of 10-20 seconds of idleing around the sky? Heres a prime example that ALWAYS happens:
Comming around on final and its lined up on the runway and I've idle'd her back. Then at the last minute I decide not to land but do a touch and go. I hit the gas and it starts to puke. Sounds like its not got the low end adjusted. It usually comes out of it and takes back off. And as long as Im given her hell, it stays runnin. Next time I do a touch and go, GAURANTEED its gonna puke and I WILL be dead stick'n it.[]

Thunderhead

Air leak? Explain more how this would effect it. Maybe not enough pressure and I have to run it too lean and its flamin' out?[]

Edwin

My Feedback: (2)

There is a way to test for air leaks while the engine is running. You need a can of WD-40. This was told to me by a mechanic friend that uses it a lot to fix other peoples problems. With the engine running at max throttle, spray around the base of the carb (not in the carb), around the carb barrel, remote needle valve, back plate, and head. If the engine sag's, that is a leak. Many times this doesnt produce any results. That at least lets me concentrate on other areas. I have also fixed a wayward carb by removing the needle valve and spraying WD-40 into the spray bar, or removing the fuel line and spraying into the spray bar to clean out any foriegn matter. Take a look at the glow plug for any anomolies like a non uniform coil. This could indicate an overheated condition. Also, check that the pressure tap on the muffler is clear and breaths ok. The engine needs some pressure in the tank to help fuel draw. 10% should be all that you need. Additional info like prop (brand and size), glow plug type would be helpful. By your symptoms, its sounds like a carb adjustment problem. But you've already done that dance, so the other things are the next step. After that, may need to send it in.
Edwin

Thunderhead

The prop I've been running is an APC 11X6 and I've ran Fox and Cox Long glow plugs. As statd before I used to run Omega 15% now Im running PowerMaster 25%.
But when I switched to the 25% from the 15% I noticed the problem even more. I seriosly doubt its the fuel, but an underlying problem that has began to manifest itself into a royal pain in the
*****.[:-]

3d-aholic

My Feedback: (7)

If your at idle for 4 seconds and you increase/rush the throttle, and the engine stops, its a low speed adjustment problem. How many turns out is the low-speed needle value currently from being "seated" A cold engine on a cold day will handle "more sloppy fuel" at idle first time out than it will once it heats up. Thats the definition of a "choke". It sounds like its loading up....

You need to define better how it stops... Lots of smoke? Dies immediately. Staggers like its choking on fuel. And when you hear it staggering, what happens if you immediately ease back on the throttle before it stops...does it suddenly improve?

Thunderhead

Yes, somtimes if I ease back up it will improve. When I gas it after idle it wants to stagger and putter, and if I ease up it will improve, but as time goes on it acts like it loads up a little more each time until easing up wont help and it will die immediately.

3d-aholic

My Feedback: (7)

That sounds like the classic "loading-up" syndrome to me. You see lots of smoke when you increase the throttle right?

[ul][*] How many turns out are you on the low-speed mixture? [*] Is the engine upside down by chance?[*] Where is the tank in relation to the engines carb?[*] Does fuel siphon automatically from the tank into the carb when the plane is in a slightly down attitude on landing?
[/ul]

If the engine is upside down and the carb is lower than the tank, then you can get to a point where the siphon is automatic and the low-speed mixture becomes virtually irrelevant.

3d-aholic

My Feedback: (7)

If you see lots of smoke the engine is NOT overheating. An overheated or overlean engine gives virtually no smoke and just up and dies quickly like it ran out of gas or died of starvation. In addition, when you try and restart it....it typically won't restart...unless you reprime it.

An over rich engine, will smoke, will try and keep running with all that extra fuel but acts like its suffocating from too much fuel. If you restart it with a nice hot glow, it usually starts no problem.

Thunderhead

ok, maybe it is loadin up. I do get a nice smoke trail on my uplines. So the low end is too rich and needs leaned out? (i.e less fuel more air)
Am I on the right track?

3d-aholic

My Feedback: (7)

Well, I would need answers to my questions before I could state that with more conviction without hearing or seeing the engine. But, my gut tells me you need to turn the air-bleed screw 1/4 turns CW until you can idle the engine for at least 10 seconds and thurst the throttle rapidly to high speed without the engine quiting. That adjustment is made after the engine has heated up and ran without the glow plug heater for a good 20 seconds at full throttle.

Also, in my opinion, no new OS engines idle very well until you have had at least 10-15 full tanks of fuel through them and some as much as 20-25 tanks. The are just so tightly made, that until they loosen up, the strong desire to stop at idle due to friction is too great. Until then, I fly with my idle high and takeoff with running stops and stop the engine after safely landing and go out on the runway and get the plane.

wldcwbypilot

Have you checked your tank to make sure your clunk is back where it should be? Then check your tank feeds to see if they have a pin holes in them, I have had a couple of engines that dogged out because of air leaks in the fuel lines, never could get them to idle. Lost tank pressure would make you have to run your engine in a very rich setting. Have you tried letting the engine warm up then pull back to an idle place the glow driver on the plug, if it speeds way up you are too rich. If your carb is the air bleed type you want to screw the low speed screw out to get more air to the mixture. If its twin needle type screw it in in 1/8 or less turns till you get no change when you apply the glow driver. Then test to see if you have good transition. In my opinion, i hate remote needle assemblies they are to variable in their working properly. Oh by the way wd-40 doesn't do a good job in finding air leaks in model aircraft engines, if your going to use something to look for air leaks try short squirts of ether, starting fluid.
wra

LearjetMech

I think I may have stumbled upon a possible solution to your problem! My LHS was telling me a story about this engine. He said there was a history of the needle vavles turning on their own when certain vibrations were in the engine. What I would do is tune the engine for good response and shut it down. Now mark the needle valves somehow, with nailpolish, to give what is termed a "witness mark". Make sure you mark both the needle and a "fixed" spot also. Go fly until the aircraft does this again. Once it does it again land it and verify that the needles are not vibrating to a different setting. I would try to do this on high, low, and air bleed if possible! Hope this helps. He told me a similar story and I remembered this post!!
Nik

William Robison

My Feedback: (3)

TBoomer:

Just a thought, but you did say the engine was worse with 25% than with 15% fuel. Could be over compressing. Add about 0.002" shim under the head and try again with the 15% fuel. But I see no reason why the second run would be more affected than the first.

Bill.

IXLR8

My Feedback: (55)

I have this same engine(four of them) and they don't run very well at all with an 11x6 prop(APC) or anything other than an OS# 3, OS #8, or Enya glow plug. An 11x6 is too much prop for it. I also had a friend that always complained about how his ran but he always ran an 11x6 on it with a Fox glow plug. When he finally listened to me and changed to a 10x7 and an OS#3 he was suddenly very pleased with it.

Switch to an APC 10x6,7, or 8 and use a OS#3 glow plug and it will probably run 100% better. Then make sure you have the low end set correctly. Most engines arrive with the low needle on the rich side so you may need to lean it out a bit.

3d-aholic

My Feedback: (7)

Sorry...but I have several OS46FX's and I don't agree. I run Fox plugs, and an 11x6 prop and it runs great....no deadsticks, immediate start, no need to reset the fuel mixture unless the weather is dramatically different.

I use an 11x6 for slow flight and and 11x8 for quick flight. If you look at the top Flite prop chart or any prop chart for that matter...an 11x6 is the middle recommended prop for a 46-52 sized engine. I use 10x6's on my 40's. The chances of overheating a 46 with a 10x6 seems like it would increase exponential and that engine will be maxed out on revs and runs like a crazy person. I've never tached the 11x6 prop but I can listen to the engine and know its up there...

IXLR8

My Feedback: (55)

Actually the prop chart for an OS 46FX recomends props from a 10.5x6 up to as high as a 12x7. All of the 46FXs I own run 100% better with a 10x6,7,8 than they do with an 11x6,7,8. Sorry.. but I have four with 2-300+ runs between them, on 15% cool power, and they simply run better and yes cooler on the 10" prop. They also have no dead sticks, will easily hand start and run perfectly every time. I have tached them, and an 11x6 runs about the same RPMs as a 10x8 anyway, but the 10x8 will throw more air over the cooling fins allowing for a cooler running engine. Try a 10x7,8(APC) and an OS #3 plug and see if it works.

3d-aholic

My Feedback: (7)

Well my engine is not having these problems so I definetly don't want to try anything if its working for me. 10x8 is on the low end of the .46 so that prop might work...but 10x6.... My OS 46 will definetly be maxed out on a 10x6. In fact, my OS 46, will pull an APC 11x8 at virtually the same RPM as an 11x6...maybe I got a good one.

Heres the top flight prop chart.

[link=http://www.uoguelph.ca/~antoon/hobby/propchrt.htm]Top Flight prop chart[/link]

IXLR8

My Feedback: (55)

By all means stick with what works. I do have "good ones" by the way, and they run perfectly, always have(even the first 15 tanks). Two strokes will give you maximum HP at high RPMs, it's their nature. Get a tach out, try different props, fly with them and find out what works the best on your plane/ engine combo and go with it. Mine and others I know of really come alive when they are allowed to rev up.