Hi - I have an OS46FX. It has a 'throttle stop screw' which is located right behind the carb. What is this throttle stop screw for?
Thanks,
phoTToniq

I remove mine and set the minimum low speed idle with the throttle trim. Leaving it in could cause the throttle servo to bind, thereby causing undue drain on your onboard battery..

I'm not sure about OS, but be carefull if removing the throttle stop as in some engines it keeps the barrel in place. (a lesson quckly learned with my Enya 4 stroke... pull-pull... "that's not suppoed to happen!?!")

but what is it actually meant to be doing?

I was told that if you tighten it down to the right setting, it will keep the carb. from closing past idle, in effect keeping the engine running.

I don't know anyone who uses it for this, for two reasons, as stated above, unless your radio is very precisely set up, it could easily cause the throttle servo to bind (draining your RX battery) and also because most people prefer to be able to kill their engine by bringing the throttle trim down, which is exactly what it would prevent.

ahh ok then thats cool because I am able to fully close the carb right now so i will leave this screw alone as I DO want to kill the engine with the tx.

Cheers,

phoTToniq

The only time I remember using as a throttle stop screw was when I was running in an engine on a test stand. Since I was controlling it directly (with a push rod) I wanted to make sure I didn't kill it every time I brought it down to idle. When I put it on the plane, I backed it off so I could kill it with the radio.

It is also called the high speed Idle screw. It was use on motors with a friction clutch.

1. The throttle barrel has a slot in which the screw is set into. This slot is cut diagonally (helically?) and allows the barrel to move in and out as it rotates. (At least in my engines). Correct me if I'm wrong, but I believe this has something to do with retaining the correct mixture at different throttle openings.
2. It can be set to allow a minimum opening as stated above. Don't bother. Use the Tx.
3. I believe it can be set to keep the throttle wide open (for control-line??)

flianbrian

I have 2 different types on my engines one has a spring and the other has a double nut holding it in place and one even has a slight taper to the barrel grove that can be used to close the barrel slightly more if needed. but on my engines this screw HOLDS THE BARREL IN if you would like to remove the barrel from the carb just take the screw out and barrel will fall into Hand. However this is not what I would like to happen in the air, if the screw was missing, hense the name it stops the throttle from comming out or throttle stop from falling on my head ect.......

Just a thought

Opps !!!!! it would not exactly fall on my head if it remained on contol rod z bend would it? hehehehe

Does this mean that the screw can be removed without any problem with engine performance?

as Checklst has suggested , you risk the barrel coming off in flight.

just wonder why you want to take it off???

Without the throttle stop screw, which keeps the throttle barrel in the carb body, you also would not have proper metering for the idle mixture. It's what rides in the groove and allows the idle needle to move in and out, metering the fuel at low throttle settings.

Some O.S. carbs have a separate carb retainer screw that only holds the throttle barrel in the carb body, and a stopper screw that's for adjusting the amount of rotation of the carb barrel. The .46 FX never had that kind of carburetor.

So nice to know that I figured out as a beginner, years ago, that there was no sense in ever touching it. That's what servos are for. Too bad the manual doesn't explain that.

Dave Segal

Hi everyone. I'm a newbie in the sport of rc flying so please bare with me if my terminology is off in explaining myself. I just bought a P-51 PTS and have had all sorts of issues, engine wise, since I started her up. First she was set at half throttle and wouldn't come down to idle. So, I reset the linkage to correct that. Now that I got it to idle, It wouldn't run past half throttle, so I messed with the 2 settings as described in the owners manual for the engine. I got that working. The radio was set at -40% for throttle trim and the idle was now too high still. I hit the throttle cut off button on my radio and the plane still runs and the throttle barrel is closed. As I was messing with the low speed screw and blipping the throttle, I noticed the barrel wasn't moving as it should with my radio controls. It wouldn't return to it's original position evry time I moved the throttle. I was at wits end at this point, because I didn't realize the throttle stop screw was loose from the factory and hence didn't notice that because there is no mention in the owners manual about that screw, so I didn't even check it. Now I'm at a loss of how to set the carb up with this screw. I notice that the barrel will come out further as I loosen this screw more. Can someone tell me how to set up this screw and how to set my throttle up to work correctly from the beginning? I am a gearhead by nature, so I should be able to figure it out on my own, but would rather leave that to someone knowledgable in that area. I don't want to send this plane up for the first time and bring it home in pieces because of not knowing what I'm doing. Oh yeah, so much for READY TO FLY out of the box! This must've been a Friday end of the shift slap together job! LOL My aileron setting wasn't set up properly from the factory either, they were operating backwards but a call to tech support got that straightened out. They went through all the settings with me on the radio and others were not set properly either. Hope this isn't a sign of what's to come when I get this plane in the air!! LOL

The throttle stop needs to be removed by the manufacturers. They are only needed on car engines when the brakes are applied, the stop keeps the engine from cutting out.

I have the same engine. Assuming it has the same carb, NO!

The Screw in question does more that just "Stop" the rotation at a given point based upon its setting. As has already been pointed out it A: hold the barel in place, and B: acts as a guide pin for the barrel rotation, thereby ensuring the correct amount of side to side movement as the barrel rotates.

I have not ever tried to run mine without this part, and Im no expert, but I assume based on the way its put together that the positional movement is in fact a requirement for the low speed needle valve to operate correctly, and the mixture to remain constant as you open it up.

The best thing to do with the throttle stop screw is to make sure it doesn't interfere with the carb barrel closing all the way and then leave it alone. If the servo linkage and transmitter end points are set up correctly it will not bind.

The 46FX uses the 40B Carb http://www.gpdealera.com/cgi-bin/wga...pgm?I=OSMG2452 and the rotor stop screw http://www.osengines.com/parts/images/25681620.jpg both determines the "track" or "path" along which the barrel rotates but can also be used to set the minimum RPM. However it is typically best left to the servo to control this point by backing off the screw to the point where the engine will cut off and then setting the endpoints of the radio system either mechanically of electronically.