bubbagates
Posts: 8162
Joined: 5/30/2004
From: Elizabethtown, PA, USA
Status: offline
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IBrake,
You already know this but I will repeat it. There should be no air at all in the lines. Any bubbles can and will make adjusting the engine hard as it will be very inconsistent. Based on everything in the first post when an engine coughs then slows to a stop it's too rich. After it dies it fires right back up which pretty much confirms that. An engine that died from being lean will not always start right back up.
This is an air bleed carb so to lean it you turn the screw out (counterclockwise). I looked in the OS40LA manual on OS's web site and there are no factory settings listed so it will be tough. On the 46AX non air-bleed carb the factory settings are 1.5 turns on the idle screw and 2 turns on the high speed needle So this may be a fairly good starting point
Set the high speed needle 2 turns open, close the air bleed screw and open it 1.5 turns.
This setup will result in a sloppy rich engine when it starts
Now start it and leave the glow driver on and get it to full throttle. Now slowly lean the high speed needle 1/8 to get max rpm then back off 2 or 3 clicks. Now take the engine to high while still leaving the glow driver on.
Let it idle for 5 seconds then blip the throttle to no more than 1/2, 1/3 is better. If it hesitates, blubbers, spits fuel then return the engine to idle and turn the air bleed screw 1/8 turn counter clockwise. Keep doing this until the engine quits blubbering, spitting fuel.
Now go to full throttle and it should now transition fairly well. Leave it at full throttle for a few seconds then go back to idle and remove the glow driver. Now once again go to full idle all the while listening to the engine. It make go right to full throttle or it may spit, blubber. Now bring it to idle again and go to 1/3 and right back to idle, If the transition is nice and quick and smooth then you are OK. If it blubbers and stuff then turn the air bleed screw 1/16th turn counter clockwise. and retest to 1/3 throttle. Keep going at this until the transition to 1/3 throttle is nice and quick and smooth.
Once you have that then retest the transition from idle to full throttle. By now it should go smoothly and quickly to full.
You should be done.
Now let it idle and see if it just sits there and purrs. The occasional miss and spit can be expected if you are getting air on the lines.
I know it sounds like allot but it usually takes about 10 -15 minutes to do what I suggested but if all things are fine then you will be rewarded with a nicely tuned engine.
If you cannot get the transition to smooth out then it's possible that the air bleed screw or it's seat is damaged.
One other thing, what prop size/pitch are you using. To big a prop on that engine and you will never get it tuned or running right
Sorry if I am making recommendation that you may have already tried
_____________________________
Bill James
Normal is not something to aspire to, it's something to get away from
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All Forums >> RC Airplanes >> Beginners >> RE: Another Question about the OS 40 LA 
RE: Another Question about the OS 40 LA - 
The guy at the LHS said almost nothing useful...he said, "The wheel toe-in is off." 
That has like nothing to do with the engine. The idle screw is in about 2mm (covering about 1/3 of the air bleed hole). Please help! I'll take pics and give as much as I know what is going on if more info is needed. 