Lancair-RCU

Ive an OS50SX thats instaled in my Blackhorse CAP232. It was run in as per instructions on the ground first plus one tank and performed flawlessly on the trainer I used to run about a gallon of fuel through it in flight. The first few flights installed in the CAP were flawless as well.
Yesterday it was sort of surging a bit at full throttle, maybe a few hundred rpm. Today it was surging quite noticeably. On the ground it idles well, although I think the low end needs to be a tad (1/8 turn at most) leaner, but on applying full throttle it picks up well then after say 5 or so seconds, really peaks the RPM. I notice several bubbles in the fuel line from the needle to the carb ONLY, not from the tank side, during this first few seconds at high rpm then the bubbles remain but get really really small as the RPM peaks. On the ground it holds a constant RPM at full throttle but surges mildly at mid range to idle RPM's. Its almost as though it doesnt reach a good peak until tank pressure has had a few seconds to build up and push the fuel out. The bubbles and lag to hit peak RPM is repeatable by reducing to idle for about 10 secs and opening throttle fully again. The needle valve has been set at 2-3 clicks rich of peak RPM, to a full turn rich of peak in 1/4 turn increments, with no difference in-flight to the surging problem. Flying inverted passes doesnt show any difference to the problem so its not a hole or leak in the clunk line above the normal attitude level.
Ive read loads of threads here about different problems people have had and subsequently checked the needle valve for obstructions, NONE found, tightened all the nipples on the remote needle assembly, none were obviously loose, checked the fuel lines for leaks, nicks or cuts and found nothing but unscathed clean fuel line. The needle valve O-ring 'appears' unscathed and in good condition, its never been out until tonight. I am using a DuBro fuel filler, that lots of people say they had nothing but problems with and others say never had a problem with, I have NO bubbles from the tank side of things so Im assuming its not a culprit here. I can disconnect the pressure line from the muffler and the line from the tank to needle valve and blow through it quite easily so there doesnt 'appear' to be any significant restriction in that department.
Its running an APC 11x6 prop for run-in and still is, but have an 11x7 to try (another club member with same engine a simlar weight plane tried one and wasnt as happy with it as the 11x6) and an 11.5x7. I recently heard of club member learning the fix for a poorly running engine and tuned pipe setup, was a bigger prop to load up the engine more. Is it worth a try here ? No tuned pipe though so maybe not. OS recommend 11x6-10 or 12x6-9.
I have also noticed some/a lot of castor oil residue on the muffler, it appears to be coming from around the muffler to engine manifold area and also some residue on the head itself from around the glo-plug gasket area. The glo plug is in tight and gasket/washer appears in good condition and the muffler bolts cant be tightened anymore (or loosened for that matter, the hex head has stripped out on one bolt so it'll stay on until absolutelty necessary to remove with brute force). Possibly its from a spill whilst hot or ? ? Ill clean it off and see if it returns tomorrow, though I doubt this part of my problem.

So far I think Ive covered all bases to solving this but need to do more in-flight testing tomorrow but if anyone can think of something Ive not done PLEASE PLEASE let me know. Other than cruddy comments about OS engines in general and what I should do with it or put it, as Im well aware there's a large percentage of people here who despise OS engines.

Matt Kirsch

My Feedback: (21)

Air bubbles are completely unacceptable anywhere in the fuel system. There is an air leak somewhere in the remote needle valve assembly, which is probably what is causing the problem.

We had a similar issue with a student's OS .40LA, lots of bubbles in that line, and even though everything LOOKED OK on a visual inspection, the tubing between the remote needle and the carb had a pinhole that was only visible if you completely removed the tubing and stretched it out. Replacing the tubing fixed the issue.

Say what you will about OS, but the after-purchase support you get from Hobby Services is hard to beat. If you can't get it sorted out in a reasonable amount of time, send it to them with a nice note describing the issue. Might cost you a couple of weeks of flying that particular plane, but better than the alternative of not flying the plane at all.

Lancair-RCU

Thanks Matt,
It seems as though some bubbles originate from the Carb end when at idle but quickly get sucked down again as the throttle opens, I saw this on my OS46FX as well but never had any problems with it. Ive closed the needle valve completely and blown in the pressure line, no leaks, I just go red in the face from trying. Ive opened the needle valve 4 or 5 turns and pinched the line from needle to carb, no leaks, done the same with carb closed and piston turned so no leaks in a really deathly quiet room and can hear no leaks, Ive just got sore cheeks and lips from trying to blow into a fuel line very hard. Short using an air compressor (only because I dont have one) to really pressurise the system Ive tried all the possible ways I can think of to test it. Obviously from my observations air was getting in somewhere. The engine wasnt hot enough for it to be methanol vaporising as I read in another post.

Ill pick up some new tubing on my way to the field tomorrow and replace it all if need be.
Ive also just ordered online a set of fuel dots, when they arrive Im going to change the DuBro quik filler though I dont suspect it, Im going to eliminate ANY possibilities now and for future problems as well. I like the KISS principle, had I know about fuel dots before getting the quik filler Id have used them.

sport10

The one thing that I have noticed is you have not checked the balance of the prop you are using. This can cause the bubbles you are having. I can also be a leaking fuel valve too. Here is a couple of things to try. Make sure your prop is well balanced or the vibration will cause the fuel to foam in the fuel tank. Another thing is to exchange the fuel valve for just straight line and see it the engine runs correctly. Cut a small piece of medium fuel tubing about a 1/8 long and slide it on the the needle valve before screwing it in. This will help seal the needle valve in case it is leaking air in.

When you switch to a fuel dot you need to run a third line from the tank for fueling. This way you will not flood the engine when fueling. Set this third line up with a line and clunk. The other two lines still hook up the same. Good Luck.

Lancair-RCU

Sport,
You're right in saying I havent checked the balance of the prop in the diagnostics.
Because I did it before it ever went on the model. It runs very smooth compared to other models Ive held for other club members while they start up. I also dont see any bubbles in the line from the tank. The tank has foam at the front and rear of it BUT, it has to slide through a former which has about 3mm gap all around the tank so its near impossible to get foam between the tank and the fuse former/bulkhead ? The tank doesnt touch it the way Ive packed foam around it but . . .
Im of to go test it now, Ill post back this afternoon.

edgeguy

My Feedback: (16)

Lancair, I had the same problem with my 50sx turns out the problem was the idle stop screw had loosened and backed out too far and was allowing the throttle barrel in the carb to vibrate a lot. When I looked down the carb with the engine running at full throttle the throttle barrel was opening and closing just enough to make the engine surge. Make sure the idle stop screw has not backed out too far. ..


Just an idea. Good luck. Bob

Lancair-RCU

OK,
The first thing I did was eliminate the DuBro Ezyfueler from the system. I think there may have been a slight, very slight, kink in that line somewhere but couldnt see it as its buried in the foam. A test flight revealed the same problems though less severe surging but none the less it was still there. Bubbles from the needle valve to the carb line also present, tiny tiny litle ones at WOT, and larger at lower throttle settings. Removing needle valve and putting a piece of fuel tubing over, and re-inserting produced way less bubbles but there were still some. Im suspecting leaking O-ring on the needle valve so a quick pack up and trip to the LHS, none in stock of course, but looking at another OS 50SX in the shop the o-ring is the same size (duh). Mine doesnt show any sign of damage anywhere and the LHS guy thinks Ive got other problems and suggests to reset the low end idle settings and top end mixture.
So a trip back to the field, wind the low end all the way in, then back out 1.5 turns, needle valve to 2 turns open and start er up. I let it idle for a minute with glo power still on then went to WOT (glo off) and set the needle valve to 4 clicks rich of peak. Back to idle for 20 secs and open it up, cough blubber and it runs, so shut down, in 1/8 of a turn on the low end. Restart and go to WOT and back to idle, let it idle for 20 or so secs and WOT, picks up smooth and clean. Some small bubbles were evident but didnt cause any rough running or surging. So off into the blue for an air test and it seems MUCH better, no surging at WOT, minor surging at mid range, pick up from idle in flight is good but is a little rough. BUT it doesnt 'seem' to be reving as hard as it did initially when it ran good. Vertical lines arent as long before running out of steam and it just sounds a little weak. Now the cowling is off so that could (probably is) be making a difference to its sound and maybe to its WOT full speed as well, it certainly seems to slow down quicker on approach to land without the cowl on.
Is there a better prop for this engine ? Will a 11.5x7 or 12x6 make it any better or worse ? I guess actually putting one on it and testing in-flight is the only way to really know.
I am much happier with it now and will wait until I can fly it again with the fuel dots system and cowling back on before I compain about it again

Thanks Edge guy, I checked on my return home this afternoon and its OK, no freeplay in the carb barrel.

Matt Kirsch

My Feedback: (21)

Do you remember how much you had to turn the low end in when you reset it? Your description just reminded me of a similar low-end issue I had. The low end needle actually affects fuel flow right up through full throttle if you have it set too lean.

JoeAirPort

My Feedback: (41)

No wonder OS ships them with the low end set so rich. It's harder to mess them up.

Lancair-RCU

Roughly 1 1/8 - 1 1/4 turns in. 1 1/2 turns out and then 1/8 back in.
So effectively 1/8 richer than it was.

Lancair-RCU

OK Heres an update a week later.
The surging problem is gone, it now will run consistantly.
Flying it today it seems anemic, like its going fast, but not flat out, uplines have no where near the pull they did. Takeoff was sluggish, like only about 3/4 throttle in the climb out.
Setting the high end doesnt seem anywhere near as powerful or distinct a peak RPM as previous testing, it just starts to die after peak.
Mixture (needle valve) is set to about 1/4 rich of peak, idle is great, pick up from idle is smooth and quick with no spluttering etc. After starting I open the throttle wide then back to idle, take the glo power off and NO change or very slight drop in RPM, pinching the line quickly at idle gives a very slight increase in RPM. WOT and hold the plane vertical and no change or very slight increase in RPM.
Compression 'seems' to be as good as it was after the run-in period, maybe better.

Any ideas people ?

Lancair-RCU

Just a quick thought/question ?
Does having the cowl off generally make a big difference to a models performance speed wise ? Maybe my 'perceived' poor running is only due to the cow being off and therefore not as fast as with it on.

Lancair-RCU

OK I can see Im carrying on my own thread here, no-one seems to know or wants to share their experience/knowledge. So Ill post my results here so maybe other might try my solution.

After 2 trips to the field and several people having a go at tuning this OS50SX without much success the final idea was to try a smaller prop. With the APC11x6 it was clearly unloading and reaching a peak in a shallow dive but anything it else it was a pig.
I tried a Bolly 10.5X6 prop and got better results but somewhat slower in flight. Today I tried an APC10x7 and it screamed like it did new with the 11x6. Defineately a HUGE improvement in performance. Why ? Other than a smaller prop so less load, I dont know why it dropped performance from its original performance with the 11x6 but at least its flying great again. Compression is excellant for a ringed engine so its not that, carb is clean, needle is not blocked although one time the guy tuning it was able to almost completely remove the needle and NO change in revs, weird we know but everything else checked out OK.

Oh and my testing indicates that performance with the cowl on is much better than off.

Cyberwolf

My Feedback: (4)

Hey guy I don't know if your still following this tread or not .Anytime you have alot of excess fuel on the muff, its leaking from the exhaust port to the muff .thus it can also cause you a surge from not enough back pressure in the tank .also will effect the needle settings .check to see if its warped ,if so place it on a fine grit sandpaper using a piece of glass and lap it back flat ,then make a gasket for it,see if that helps . BTW if the muff was leaking you will need to readjust all of your settings to regain the power you had plus reliability.Good luck
C.W.