hey gang.. I have a O.S. 55AX that wont stay running.. Twice in flight it died and I landed the plane.. good to go.. Now, I'm bringing the pair back out to see if I could find the issue.. My problem is that it will only run at wide open.. I'm using 15% fuel and no issues with any of my other engines.. Ive put all the screws back to Factory settings [email protected] out and [email protected] out.. its hard to get going at all but, will run wide open, as soon as I start lowering the RPMs it dies.. I thought it may be a tank issue, changed tank and even tried a dummy tank at a much higher than needed position to make sure it wasn't a flow issue.. glow plug has been changed also.. Maybe not hot enough? any help is greatly appreciated..

This is your problem those are only recommended starting positions. The high speed needle during tuning will be leaned from that setting on the first startup considerably and how much will vary on your local density altitude and temperature. The engine must be adjusted from that starting position. You are running to rich.

Get experianced help and mentoring.

John

More than likely you have an air leak. At WOT, tank pressure is highest and vacuum in the intake in highest, therefore you are able to find a needle setting that will keep it running. But as soon as you drop the RPM the engine doesn't get fuel, so it dies. The common culprits are the backplate, the carburetor mounting, fuel lines and stopper, needle valve o rings, and a bad front bearing.

what size prop are you running?

Another possibility you should confirm is that the Low Range needle (LS) that you set at 1.5 turns out actually is the Low Range needle(LS).

All the AX's except the .46AX use a new series carburator that utilises a different principle for the LS metering. It is on the opposite side of the throttle arm and on the tip of that cone near the fuel inlet nipple

This is a considerably different set up than the common setup with a typical double needle midrange and lots of folks get hung up on this point.

John

I have always used an a3 plug I think they have been renamed to os #6 the plug is hot enough to keep running especially with my engines mounted sideways. when running wot lean the hs needle til you get max rpm and then three clicks richer from there. check idle and adjust the needle after it has rested at idle for 20 seconds. is transition loggy like it is loaded up or does it stall like it is lean.

John: Do you, per chance, have a picture of that?

CGr.

Hi CG, Just got back from the field this morning flying my little nostalgia airplane, with a .35AX on it and I will make some photos in a little while.


John

Hey CG here are examples of a .35 and a .55AX's showing the left side of the engines (facing forward) and the midrange screwdriver slotted needle is clearly visible in the end of the cone that the both the fuel inlet nipple and the main needle are also located. I am pretty sure this is the case with all the AX's except the .46. I only have one .55, three .25 and three .35AX's.

The last two photos (correction the second and forth) are both sides of a .25FX which uses the older carb and is the a setup widely used by many manufacturers. The slotted mid range needle is clearly seen inside of the throttle arm barrel, right side and I course I am sure most folks are familiar with this setup

John[8D]

Ah, THAT screw adjustment! Got it. For some reason, I was thinking it was on the other side.

I think I need a little adjustment on one of my engines and was wondering what one was the LS needle. Now I know.

Thanks, John.

CGr.

Your welcome CG. That has caught a number of folks around here and they were adjusting either the throttle arm set screw or the throttle barrell guide screw which of course does nothing. Have noticed that confusion on the forum also at times.


John

Well, that certainly explains why I have been having problems with the engine quitting after a few minutes of idle operation. I've been adjusting the wrong thing. Good stuff.


CGr.

CG, that will mess things up every time. I like the AX low speed needle a lot better then the old FX. It's how they have been doing it on the four strokes and you can set it much better/easier.

Get yourself an OS F plug.....lots, and lots of folks I know (that can tune a glow engine with the best of them) including myself had issues with flameouts even though the .55 was tuned spot on. The F plug solved that issue for all of us-just search and you will see.

Engine tuning/diagnostics are very difficult to teach over a forum. The best way is face to face with an experienced mentor. Are you a member of a club or do you have access to someone that can help you locally? If you do not I would be willing to help you if you are willing to make the 105 mile drive north to get here. PM/email me if you are interested.