OS .46FX Engine troubles
 

HI- I am having trouble keeping my OS .46FX running. It quits and when we check, there are sometimes air bubbles in the line. I changed the tank and all the fuel lines and will try it tomorrow. We have adjusted everything and we have to dead stick almost everytime we land. The last few times, there has not been the air bubbles and it starts right away when we check it. It is in a Nexstar Trainer and it doesn't help my landing confidence much. It runs great on the ground and idles fine and flys great until I pull the throttle back to make my approach and then quits. In our adjusting, it seems to run the best with the needle valve out only 1 - 1 1/4 turns. Seems a little lean to me but that is where it runs.

Any ideas would be appreciated.

RE: OS .46FX Engine troubles
 

Not sure if this has anything to do with this but the fuel tank stopper screw in my nexstar loosened up and I didn't notice til fuel leaked out of tank . Tank may be losing pressure

RE: OS .46FX Engine troubles
 

How's the compression? Some time ago the .46FX engines were plagued with sleeve problems. The lining on the cylinder sleeve would be worn prematurely and would need replacing. It happened to one of my engines and the symptoms were low compression and trouble keeping it running.

DaveB

RE: OS .46FX Engine troubles
 

When you replaced the fuel lines, did you replace the line inside the tank with the clunk on it ? Also, did you replace the line between the needle valve and the carb ?

If those lines were replaced, it sounds like you are losing pressure to the tank. I would pull the tank and make sure the screw holding the cap on is tight. I would also do the following: Block/plug all the lines but one. Put the tank in a container of water and hold it underneath the water. In the one line that is not plugged, blow into the tank and see if there are any bubbles. If there are, there is your leak. If it is the tank itself (seam, etc), I suggest replacing it. I have not found a repair to a tank to hold up.

RE: OS .46FX Engine troubles
 

Have you adjusted the low speed needle? Mine was pretty out of whack to start.

RE: OS .46FX Engine troubles
 

When you go from idle to full throttle on the ground (holding the plane firmly) does it hesitate and burble or does it accelerate smoothly? If it hesitates then you may be running rich on you low speed needle. This will cause fuel to build up at idle and cool or foul the glow plug and make it quit.

Or your idle rpm is simply set too low.

Andy

RE: OS .46FX Engine troubles
 

Your engine is out of adjustment. Even though it may sound good, it can still be way off.

RE: OS .46FX Engine troubles
 

My advise, either borrow a tach at the field or buy one. You don't really know what is happening without one. When I finally broke down and bought a tach, the difference between what I thought I heard and what the tach saw was amazing. You don't really know what is happening without one. For my 46FX engine with an APC 11-5 prop I adjust for 14,200 rpm. If the engine won't turn the prop that fast, then something is wrong! The first time I brought the tach to the field I first adjusted the engine by ear and then took a reading. Then I adjusted again by using the tach. By ear I was getting around 12,000 rpm. With the tach I was able to fine tune it to 14,200! The increased performance was very noticable! [8D]

RE: OS .46FX Engine troubles
 

Thanx for the input. I'm off to the field with a new fuel tank, all new fuel lines, new fuel, and a readjusted idle. Compression is good and the engine is only a few months new. When we tached it last week we got about 11500 and the guy helping me tune said that was ok for the longevity of the engine. There are several tachs so will check that again. We had some hesitation on the ground test and adjusted that out but only ended up with one turn on the fuel needle. I really would like to run a little richer but then the hesitation comes back

I'll let you know.....D

RE: OS .46FX Engine troubles
 

If what you have already done does not fix problem and engine hesitates going from idle to full, then try leaning idle mixture slightly. Turn in 1/8 cw increments and see if this helps. Set top end mixtur first though and it will need to be checked after low end is finished. OS usually comes from factory rich at idle in my experiences. good luck and let us know what you find out. ;)

RE: OS .46FX Engine troubles
 

Just a quick note. If you have air bubbles in the line after the engine as stopped, that might not be a big deal at all. Espeically if it quit in the air. The air might just be coming back up the line from the carb end.

You want to look for airbubbles while the engine is runnig and drawing fuel. If you have air coming from the tank, or solid fuel from the tank to the needle, but air between the needle and the carb, that's an air leak you want to fix.

RE: OS .46FX Engine troubles
 

I had to lean the low end on my os46 a bit to get it to run right. Its the small screw inside the barrel that your throttle servo rotates.

Remote needle valves let fuel drain back to the tank when theres no draw on them so some bubbles when you first start up or try to prime the engine is no biggie.

RE: OS .46FX Engine troubles
 

11,500 at full throttle sounds like a very rich setting for a 46FX to me. The most common causes of engines quitting in the air is from the engine leaning out. However I found out that if the setting is too rich, at lower throttle settings the engine can load up and the engine can quit as easy as if the setting was too lean. My suggestion, lean the setting up so that you are getting at least 14,000 and see what that does. Don't worry about long life at the higher rpm, I have been running mine going on 6 years now and the engine still runs like new. [8D]

RE: OS .46FX Engine troubles
 

Well Fastsky, he's gone flying for now. We don't know what prop he is trying to turn either. Probably too rich all the way around from the sounds of things. Don't need FULL power on a trainer but he will be more reliable if he gets closer on the tuning and just backs off a click or 2 on top end IMHO. Idle reliability is more important right now than peak power but proper tuning is important. Lets wait and see how he does today and go from there.

RE: OS .46FX Engine troubles
 

Ok, I am new to the forum and flying.... What is IMHO?? I've seen it before but could not make it out from the conversation..

Got out to the field today and 3 of us hovered around the plane and started it. We adjusted just as you have suggested and got the engine running well, however, when we brought the throttle back from anything from 1/2 thrtl. to full thrtl., it would die. It appears that there may be an air leak in the needle housing. It is plastic, screwed to a thin bracket on the back of the engine on this particular engine. My other OS .46 has a metal needle valve assembly on a plate bolted to the back of the engine. The air bubbles moved back toward the tank from the needle valve and while the engine was running at any speed above idle it worked just fine and cleared the bubbles for the most part but when the throttle is brought back, the engine stalls. We took apart the tank again and re sealed it and checked all the fuel lines. We even attached an external tank and had the same trouble but not as severe. We are snowbirds in Yuma AZ and are leaving to head back north on Tues so I have run out of time. I have another engine which I will try when I get home and I also have a new needle valve assembly to try.

This is a great learning experience and I really appreciate your help out there. I could have flown today but just didn't think it was a smart thing to do. So, now I have to wait for a couple weeks to deal with this and get back to my training.

RE: OS .46FX Engine troubles
 

IMHO - In My Humble Opionion

It sounds like the low speed mixture is way off, probibly too lean, but it could also be too rich. The low speed screw is the small screw inside the throttle arm. It's very sensitive, you should adjust it a 1/8th of a turn at a time. Try backing it out a little. If that doesn't help or it gets worse, try going inwards.

If the engine just quits suddenly, that's probibly too lean, which is what I think is going on. If it sputters first, it could be too rich, so try screwing it inwards.

RE: OS .46FX Engine troubles
 

The following should be done with immense respect for the moving propeller, OK?

Start the engine and get it running and peaked at top end, then go 1-3 clicks to the rich side. This is usually a good flying setting.

Slowly reduce throttle until you get to the point where engine begins to stumble but still runs.

Using forceps or needle nose pliers or similar, pinch the line between the needle and the carb. You do not need to pinch off completely for this but must be noticeable.(You are simulating a leaner setting by cutting off fuel)

IF engine is too rich at that point, the engine will accelerate briefly and then may die (depending on how much you have pinched and how quick you release pinch). Adjust idle mixture to lean engine 1/8 turn. Retune top end and repeat this step.

If engine is too LEAN at that point, the engine will immediately fall off and quit without accelerating.(may be able to save by releasing pinch). Adjust idle mixture 1/8 turn to RICHEN engine. Repeat tests as needed.

Repeat as needed until you can get reliable idle with smooth transition to full throttle. Hi speed needle should be set first.

This method has always worked well for me. Keep us advised.

RE: OS .46FX Engine troubles
 

As I first mentioned, I still think you low speed needle is off, but something else occurred to me.

Let me restate what I believe you said to make sure I have things right. Your engine will run fine at full throttle and is properly adjusted at the high end. When you reduce the throttle it dies and you see air bubbles in the line that migrate back toward the tank. That indicates to me that you may have a venting problem with the tank. The engine doesn't "suck" hard enough at less than 1/2 throttle to draw fuel out of the tank and the tank tries to pull air back through the fuel line. Assuming your low speed needle is ok you really need to look at the vent. Check for kinks in the line. Also check to make sure the brass tube in the tank isn't kinked.

RE: OS .46FX Engine troubles
 

In post #9 he stated that he replaced the entire fuel system.



Davebart- also make sure you don't have any loose screws on your motor (including backplate) and carb is on tight too.

RE: OS .46FX Engine troubles
 

Actually, ksechler has a good point. A vent problem would cause this. Assuming the tank is fine, check the muffler tap. Make sure you can easily blow air in to the muffler. It's not likely, but it's possible that the pressure tap has become clogged, or has a burr or something block it.

bruce88123, good technique there. I like it. I think I'm going to add it to my inventory of tricks worth passing on.

RE: OS .46FX Engine troubles
 

Thank You,

Remember the MOST important part: Keep Out Of The PROP!!!!!!!!!

RE: OS .46FX Engine troubles
 

My initial thought was in line with most of the others, the low speed needle is not tuned correctly.

This statement strengthens my belief that the engine is probably not tuned correctly.
Did you attempt to correct the hesitation with the high speed needle? The high speed adjustment needle is for WOT (wide open throttle) only. Adjust this for 200-300 rpm's below peak. Then adjust the low speed needle for smooth response from idle to WOT. The engine should be able to idle for 30 seconds and then have good transition when the throttle is quickly opened to full. If it sputters or stumbles, the low speed needle is too rich. If it just simply dies, the low speed needle is too lean. Every new .46FX that I have tuned was very rich on the low end from the factory. As mentioned, only adjust the low speed needle an 1/8 turn at a time and do it with the engine OFF. The low speed needle is too close to the prop to safely adjust with the engine running.

RE: OS .46FX Engine troubles
 

I think I have the same problem, I need to work on it, But It is something I think ALOT of plane go threw, we flew today and all 4 landings were dead. But it landed so thats good. But I think I am gonna go work on it as my instructor said i should.

RE: OS .46FX Engine troubles
 

Hi guys. Again, I thank you for the great discussion and ideas. Bruce88123 has a very clear explanation of the tuning proceedure. I look forward to getting back home and onto the bench to finally resolve this problem. One of the guys commented on the small diameter of the tubes coming thru the fuel tank stopper so will change those out and check the venting. Thanks again.

RE: OS .46FX Engine troubles
 

Std tubing size should be fine. If big enough to support full throttle, leave them alone. Actually, I didn't find that comment anywhere. If lines are too big it will effect vacuum draw of fuel. [:'(]