Calvinman

Hello

Getting close to going for the first flight of my Ultra Sport 40, and was runnung the engine, a OS 46 FX and could not open it up without it dying usually at 1/3 to 1/2 throttle. checked all plumbing, found a hole in the line at the barb of the needle valve outlet. Changed line out and This made no difference.

I finally took off the pressure line and tried blowing into it only to find this made the motor cut out at even a lower throttle settings. So I tried it without having the vent line attached to the muffler and it runs like a top?? I took the muffler apart suspecting the baffle was in backwards, but no it is fine.

I am mystified and don't really know what to do exept to leave the vent line unattached to the muffler tap and try flying like this. Any insight would be greatly apreciated.

Calvi

Calvinman

Ok, I am going to bench run the motor tonight to see if it is the motor or the tank installation. I am running 15% nitro, cool power I think. I used to always add a little klotz to my fuel, I think I am going to start again. I just put a new # 8 in the motor but may try another new one. The fuel must be good cause our old worn out FP40 runs like a top on it. Dang engine!

Calvi

da Rock

Is it a new engine?


Checked the muffler fitting? They get plugged sometimes. Lack of muffler pressure can be the cause of poor throttle response.



Checked the carb attachment to the case? Loose lets in air.

Scirocco14

It sounds lean. Open the needle a couple of turns and see what happens. What have you got to lose?

Calvinman

Hi Guys,

I checked the pressure fitting on the muffler, removed the carb and the O ring looks good. No this is a used engine, and looks to have very little run time. All in all the engine seems to be unsensitive to needle valve changes. I have a plastic T in the line for a fuel dab, I will check this. Does anyone know what the head temperature should be? It almost feels a little hot to me, I will use a temperature scanner on it tonight. It will idle all night, but will not shut off when the throttle barrel is closed(hmm almost sounds like that carb O ring.

Calvi

Scirocco14

When it's idling, what happens if you pinch the fuel line for a second or two? It should speed up slightly and then return to idle. If it simply dies when you pinch the line, it's too lean. If I recall , this engine has a two needle carb. The idle needle might need to be opened up slightly if it's too lean at idle.

Is the throttle stop screw allowing the barrel to close all the way? This might explain why it still runs with the barrel 'closed'.

Good luck!

Mark

Calvinman

Hi Mark,

I was going to try this but can not get to the fuel line in the Ultrasport. I have the Motor out now, have run it and discovered it is way too rich when the muffler pressure is hooked up. This makes sense, but now with the pressure tap hooked up I only need not quite one full turn on the needle valve.

I am going to try the pinch test now that I have it on the test stand.

Calvi

Scirocco14

I carry hemostats with me to the field to help me pinch fuel lines, especially in planes like the Ultrasport, which I also fly.

One other thing is to check the backplate and make sure the bolts are tight and the gasket is in good shape. An air leak on the backplate can also drive you nuts!!

Mark

Calvinman

Ok did the pinch test and it sped up for a few seconds and died. The engine does die when the barrel is closed, I guess it is harder to see with the 90 degree install on the ultra. I will set this up to allow killing the engine with the radio when I pop the engine back in.

Calvi

Scirocco14

Did it take the throttle past 1/2 way?

Calvinman

Yes I got it all the way to full throttle and now with the pressure tap hooked up and my odd needle valve setting it is far more responsive to throttle changes and seems to be making full power. I did check the back plate yesterday and gasket is good. I think I may have it now. I am reinstalling the motor as I type and will report back when I run it up back in the model.

Calvi

Calvinman

Well she's running like a top now I am all ready for the maiden flight, just have to hope for some warmth for one last flight(or two)of the year. Thank you all for your input, I apreciate it!

Calvi

Scirocco14

Glad to hear it!

jester_s1

Everything you are describing says "air leak." I've learned that any engine that doesn't consistently respond to needle valve changes either had bad fuel or is leaking air. Trying to tune it is a complete waste of time. My standard procedure is to replace all o-rings first and tighten all bolts first, and if that doesn't work I start suspecting that some old congealed castor is stopping up a fuel passage or the muffler pressure line. That's assuming that I don't see any bubbles in the fuel line. The last possibility is a bad front bearing that is letting air leak in.

Calvinman

Hi Jester, Yes I agree with what you are saying. I have been over the engine and can not see anything wrong. I too have been suspecting fuel but it is a fresh gallon this spring and it runs a couple of older higher mileage OS's like a champ. No bubbles are visible when the engine runs and now with the oddly small high speed valve setting it idles down to a very slow, very reliable idle, accelerates like one would expect and seems to be making lots of power. Of course this is just a run on a bench stand and then another run with the plane strapped down to an old table. The proof will be when I get a few flights on it. I am wondering if it is possible that the previous owner of the engine tightened down the needle valve and opened up the seat? Is this even possible?

I know I said I could not get the engine to die by closing the barrel, but I was wrong, the light was bad and with the 90 degree installation it was just hard to see, on the bench it killed the engine as soon as the barrel closed. When I reinstalled the engine I made sure the barrel closed all the way when I hit the kill engine button on my TX.

I sure hope my engine blues are solved, thank goodness for this forum and the good people who are willing to listen and give advice. I will report back on the maiden if it happens this fall, just need a break in the weather

Calvi

da Rock

Doing the pinch test when the engine is at idle tells you whether or not the idle needle is adjusted correctly. You pinch the fuel flow off completely. If it's rich, the rpm increases before the engine quits. You're observing whether the needle is rich or lean. It speeds up before cutting because when the fuel is cut off the mixture goes from too rich to optimum to way too lean (lean like as in "none"). When it goes through optimum is when it speeds up.

The idle needle being too rich holds back the idle speed. When the throttle opens, the too rich idle flow keeps throwing in too much and chokes down the overall mixture. And the engine has been loading up at idle. The load is pulled in when the throttle opens. Lots of bad happens.....

If your idle needle has never been adjusted, there is a good chance it's too rich. OS sets them on the rich side at the factory on purpose. I've never seen one too lean ever, and from experience with curing 46AX engine problems, almost every one was either fuel system problems or too rich idle needles.

Still think it's a lousy engine?

Calvinman

Hi da Rock, I love my OS engines, never had a bad one yet, the pinch test seemed to show the correct results with a slight engine speed increase before dying. I am sorry if I gave the impression I was blaming the engine for my lack of ability to get to the route of the problem, just a little frustrated I thought it was idling rich too as you say an extra rich idle mixture will do that(low idle speed), but will give a flame out or at the very least lousy throttle response when rolling open the throttle. As stated above the engine seems to be purring along like a good OS should now(time will tell though)


Calvi

VCScott

Some times a little bit of garbage can get through and lodge in the needle valve causing a lean condition at part and full throttle with needle being unresponsive when turning out to richen the mixture.

I've had this problem before and seen others have it as well. The easy fix is to remove the needle and pump some fuel through it and flush it out, (usually works).

It could be you had something similar and it came out while you were fussing wit the carb.

Good luck with your Ultra Sport. Great plane!

Scott

bikerbc

Yes the Ultra Sport is fantastic plane and the OS 46 FX is great engine .. The US 40 and the OS 46 FX should be a awesome combination once you get the bugs worked out .. Good luck.. I hope you get it in the air before winter hits ..