acdii

Was at the SIG Flyin and first flight of the day, the engine ran fine, later on as the day warmed up, with high humidity, I could not get the engine to run well, it sputtered, ran slow, and could not get any RPM out of it. I didn't see any air in the fuel line, and it idled OK, but the high end either would not get up there, or it would nearly quit or quit if I didn't cut the throttle back right away. Not sure what to do with it, nothing I did with the LSN or HSN seemed to matter, and what is strange is that it ran fine in the cooler temps. I noticed the last few flights that it was a bit erratic in flight, though never died. Running 15% Wildcat in it since day 1, and use the same fuel in my Saitos which all run fine.

What can I check on this before wasting fuel trying to tune it? I already replaced the GP with a FOX Miracle, and that made no difference, however, if I leave the igniter on then I get more speed out of it and better transition.

Hobbsy

My Feedback: (102)

Normally when backing the throttle down, "rescues" it so to speak, that's a sign of too lean. Here is a, maybe.

Note bottom of page 21 here

http://manuals.hobbico.com/osm/fs-52s-manual.pdf

jaka

Hi!
Change to a new glow plug (OS F) and set the high speed needle again.
What prop size do you use? 12x6 might be to large... A 12x5 might be more suitable. Best props are APC, RAM or Graupner G-Sonic.
How is the cooling of the engine? Engine built in? Pictures?

airega1

My Feedback: (204)

Seems like the plug isn't hot enough, use an OS F or Enya #3 also if it slows down after removing the igniter it may be too rich on the low side

Hobbsy

My Feedback: (102)

w8ye had similar issues with a couple of .52's, it was not the plugs, it seldom is.

acdii

I had an OS F in it, which I put into Saito, and it runs fine, so not the plug. When I start it and remove the igniter, the RPM's don't drop, which makes it seem as if the LSN is correct, and like I said, it ran perfectly fine in the morning when it was cooler, humidity was the same all day long, only difference was it was 10* warmer when I tried it again. It seems like it may be sucking air in somewhere, so going to replace the fuel line as it seems a bit soft, and see if that helps. Its the high end that has issues, it will sit and idle all day long.

Hobbsy

My Feedback: (102)

AC, just out of curiosity, have you backed the HS needle out one half turn and then re-set, Thanks

acdii

Yep, I tried all different settings on the HSN with no effect. Its turning an 11x7.5 APC, and I am not getting the RPM's I used to either. Valves are adjusted correctly, forgot to mention that. Its something with the fuel system, the plugs are good, prop is good, valves are good, and it idles well, just no top end.

Jaybird

I have an OS 48 four stroke with a similar problem. My last flying session I removed the tank pressure line from the muffler (plugged the hole with a short piece of fuel tubing and fuel dot) and it ran much better at both high speed and idle. It produced more power and ran much more consistently. It might be worth a try if you have the tank pressure line hooked up.

Jaybird

acdii

I tried removing the pressure line, thought about that too, and it actually ran worse, which leads me to believe it is sucking air somewhere.

aspeed

If it runs fine when cool, I would suspect that it is overcompressed, not an air leak. On a two stroke it is easy to add a shim. A four stroke? I don't know, maybe a cooler plug.

acdii

Well that doesn't make any sense. I have had this engine since 2011, and have hours of flights on it, it just recently started acting up. If anything it would start to lack compression, not gain it.

hsukaria

One possibility is that some dirt is partially blocking the carb jet. Try cleaning the carb out. If you are using an in-line fuel filter, clean it or replace it.

Another possibility is what was already mentioned being the prop is too big. As the ambient temperature increases, the air density drops and subsequently, power ls lost.

acdii

More inclined to it being dirt, which is a huge possibility, than prop size. Been flying it with the same prop for a few years now and never lost power. As I mentioned before, if the igniter is connected, I get my high end speed. I have been using this engine since 2011 on my LT-40, and only recently has it been running a bit off. Mechanically its in great shape, so only thing that it an be is the fuel system. So I will pull it off, and take the carb apart and clean it, replace the fuel line and see what happens. As far as the prop size, its 11 x 7.5, which is the sport size for this engine, it can spin a 12x6.

757jonp

My Feedback: (48)

I vote for trash in the needle valve....

hsukaria

happened to me before...

Hobbsy

My Feedback: (102)

When all else fails refer to post #2.

jeffie8696

I want to know how an engine keeps running if you plug the vent line on the tank

aspeed

Compression ratio. Not from leaks. Adding or subtracting shims makes a difference in hot humid weather, as does the performance.

hsukaria

Jeez Dave, you're gonna make us read the manual?

Hobbsy

My Feedback: (102)

Hey there H-man, my son, when he was little would say, "read the constructions Dad".

jaka

Hi!
I agree! It is seldom the plug that is the culprit more likely it's a leaking rubber sealing on the tank or faulty fuel line. The rubber gromet is a weak point on most tanks. Tettra tanks does not have this weak construction.
Also take out the high speed needle and blow through one of the other fuel lines to get rid of eventual dirt inside the carb.
I would replace the tank (170cc) with the best tank possible either a Tettra "Bubble-less tank or an ordinary Tettra tank, but not bigger than 200cc.
Mounting position is also vital for good reliable engine runs. Mount the tank according to the "Tank mounting rule".
With a good tank set-up there should be no air bubbles what so ever in the fuel line.

Jaybird

It doesn't. If you plug the tank vent/pressure line then the fuel going out creates a vacuum inside the tank and fuel won't flow after a time. The suggestion is to remove the pressure line from the muffler pressure fitting and let the tank vent freely. The port that is blocked is the one on the muffler so that exhaust residue doesn't spray out the pressure fitting.

Jaybird

aircraftbuilder67

My Feedback: (6)

Have you tried fresh fuel? I had issues of some similarity in the past with an OS 48 four stroke. Went through a similar evolution of trouble shooting and found that when I went to a fresh jug of fuel, all was good again with the world! One thing that I stopped doing was returning fuel from the tank back into the jug if I was done flying before completely running the plane out of fuel. I suspect that ambient humidity and some combustion residuals made the fuel less than ideal for reliable performance.

Good luck!

hsukaria

Speaking of muffler pressure tap, make sure that the pressure tap nipple is not clogged.