I have a low time OS 46 FX (about 1/2 gallon through it) I have had since new. After the using for the last time last year, it was run dry of fuel, after run oil put in and stored in a dry location.
The engine HAD BEEN running last year with the main needle open 2 1/2 - 2 3/4 turns. Low end has not been touched since it was set. The engine is in a new plane mounted sidways.

Problem: It will not run beyond the prime.

I have done/checked the following and am at a loss on where to go from here.

New OS #8 plug (verified the plug is good - All coils, except the top 1/2 are lit and bright)
Fuel is getting to the carb
Fuel is fresh (Jug was opened yesterday and put on the field box)
Fuel tank/carb height is correct
Compression is excellent
Made sure the main needle valve has no junk/crud in it. (Removed and cleaned the needle valve, blew out the housing and visually verified the housing is clear and there are no burrs or anything on the needle valve.)
Replaced ALL the fuel lines, including the tank lines and made sure they were tight
Made sure the clunk was clear and free moving (tank is new)
Pressure tested the tank, everything is tight - no leaks
There are no kinks in the lines
Used the power panel with the votage set a 3 volts for the glo plug.
Tried various main needle valve settings up to and including 4 1/2 turns - no difference


The engine primes easily. It runs out the prime, then quits. Any ideas on where to go from here ? It SHOULD run, but it isn't The engine ran great before I put it away last year.

Last year I had a student with a .46 LA, similar problem. After considerable trial and error, we confirmed that the engine would keep running on my fuel (or his other jug of fuel) but not the fresh new jug of fuel.

Why is it that the tank is new? Would anything have gotten into the carb or crankcase from a previous tank?

How about friction? Is there any spinner contact with the cowl? Any possibility the engine was dropped on the nose of the crank, shoving the bearing back & allowing the prop mount to rub the block, or the crankpin to rub the backplate?

Good luck with this one!
Dave Olson

The next things to check are for leaks in the rear cover gasket (loose or missing bolts) followed by checking out the low speed needle. Put a clean piece of fuel line on the carb nipple and see if you can blow air into the carb at all but the fully closed position. There may be a blockage in the low speed needle if you can't blow through the nipple.

Assuming good fuel, if an engine will only burn out the prime, then it's just not getting fuel. If the fuel system doesn't have any blockages or air leaks bad enough to prevent fuel passage, then it's in the carb. The carb is either blocked or is just very badly-set. Make sure the needle valve assembly doesn't have trash or debris that blocks fuel passage. Clean as necessary.

One common mistake is having the idle mixture set much too lean. At full throttle, you should see about a 2-3mm gap between the needle and the nozzle. This is a basic, rich idle mixture setting. Open the high-speed needle 2-3 turns, start the engine at 1/4-1/3 throttle, advance to full, and then work on the breakin process until you can lean the engine to just rich of peak RPM. Once there, you can retard the throttle and work on getting the idle mixture set. Since it's now known to be a rich setting, you know you'll have to lean it. You should be able to get a good idle RPM and mixture setting that allows good acceleration.

The tank is new because this is a new plane and my other tanks were either too large, too small or the wrong shape. I needed a rectangular/square tank that was about 2" high and 3 1/2" - 4" wide. The closest one I had was an oval shape.

All the bolts on the backplate were tight and the carb was tight and I verified the carb was clear by blowing through it and both ways through the needle valve. I removed and replaced the muffler bolts (using locktite) and inspected the muffler - no sign of exhaust leakage. The low end has not been touched. It was "dialed in" for the idle, etc. when I had the engine in a different plane last year. I even put some vasoline around the backplate and the outside of the carb in case there was a problem with the gaskets possibly being cracked/leaking. The only thing that may/should require changing is the high speed needle setting. The engine has not been crashed or even had a prop break on it. I changed planes because I was having trouble controling the plane it was in and didn't want to crash it (Cap 232 - it is too much plane for me right now).

I had it at the field today and tried 2 different brands of fuel with the same results. I use Powermaster 15%. I tried Byron 10% and Omega (Cool Power ? - green bottle) 15%.

Two of the local engine "gurus" were also at the field today and neither one could find anything wrong either (we also tried a Fox Miracle plug, K&B and McCoy plugs).

The only thing I haven't done yet is to pull the head. The head gasket should be OK though since the compression is excellent.

Campy:

It will sound fatuous for me to say it, but you have missed something in your checks.

Open the HS needle another four turns and ipen the throttle all the way. Then with fuel in the tank pit your finger over the engine's air intake.

Without glow heat turn the engine by hand, keeping the intake blocked with your finger.

Either of two things will happen; the engine will pull fuel or it will not.

If it pulls fuel you had the main needle too lean for the new installation. Start the engine and set it as needed.

If it doesn't pull fuel there are still two possibilitiesx.

Leave the throttle wide open, put a length of fuel line on the carb fuel nipple and see if you can blow through it. If you can not blow through it the carb has a blockage, you missed it in your earlier checks.

If you can blow through the carb, again two possibilities.

Connect the end of the hose that went to the carb to the lline from your fuel pump, just "Bump" the pump in reverse. It should immediately fill the fuel line, and after stopping the pump fuel should remain in the line. If it does not pull fuel immediately, or if the fuel runs back to the tank, you have a leak in the tank or hoses. If it pulls fuel and the fuel stays in the line you have an engine problem.

If you are down to this point and there really is no external leak on the engine, pull it off the plane and place it in the trash can. You've probably been bitten by the famous OS ABN liner peeling syndrome.

Actually, if it has peeled and you want to keep the OS, order the piston and liner set for the Magnum XLS 46 from Hobby People, it's true ABC and it drops into the 46 FX. But the p/l set is almost $40 and the complete engine is $70, in my opinion it's better to toss the OS and get the complete new Magnum.

Hope at least some of this will help.

Bill.

Theodore,

My previous OS.46FX used to run with the needle open only 1 1/4 turns from closed, on 5% nitro fuel.

If you need it open that far even on 15% nitro fuel, that requires a richer mixture, you may have an obstruction in the needle housing, or elsewhere in the fuel's path. This, assuming that you are using the normal, medium, 3/32 I/D silicone fuel line.

BRW, the units on the scale of the Tower Hobbies panel, are Amperes; not Volts.
This is the current; not the voltage and it should be adjusted so the plug glows bright orange; not yellow, or red.

Also, don't use any fully synthetic lube fuel in your engine (green Cool Power...), OS and even Morgan recommend only fuel with a part Castor oil lubricant package, for your engine type.

You're missing something. Disconnect the pressure tap on the muffler. Use a fuel bulb or something and see if you can push fuel into the carb. If the fuel's getting to the carb then there is probably a problem with the carb. Disassemble it and clean it. You may have some debris or residue clogging up the spray bar.

I just thought of something else... You didn't connect the fuel line to the overflow and the pressure tap to the clunk did you?