I noticed after a flight the other day that the idle stop screw was gone out of my Super Tigre .40. It must have vibrated out. It seems to be running fine and I have noticed no change in operation. What do you think, big deal or not? It doesn't seem so to me.

Thanks.

Those screws very often hold the rotating drum in the carb body. Their point often runs in a heilical groove in the drum and serve to move the drum a controlled amount sideways that matches up with the amount the venturi is opened.

No matter what brand of carb, it is wise to verify that the loss of that screw isn't screwing up other things or might not risk other more important problems. On your ST, try to pull the drum out from the side.

But keep in mind that some carbs shouldn't be affected at all by the loss of that screw. And it's possible your ST carb is one of those. I'm pretty sure their barrels on most of their carbs don't move laterally.

And with our R/C throttle control, an idle stop on a carb is really a waste of time and a setup for a problem. There really is no reason to have the carb limit it's own closure. Our radio should be adjusted to give perfect WideOpen and perfect idle (which requires the throttle not be stopped early) and engine shutoff. And what additional closure should be available? That sucker can cause a big problem if it keeps the engine from shutting down, and at any other throttle position it's worthless.

I will check the lateral movement and make sure but I don't think this is an issue. I agree that the radio is in complete control of the throttle position. That was the first things that I checked out when I noticed that it was gone. Thanks for your help.

You DO need it to prevent the barrel from coming out.

Order another one with spring and lock tite it in place.

On my O.S. and Magnum engines there is a screw that fits the sprial grove in the barrel and another for idle stop. The only adustable one is idle stop and I back it out and control the idle with the radio. I'll check my TT 91 and a couple other carbs I have to see if there is any that usese one screw for both purposeses.

Don

OK, I got a susprise. The Magnum 70 four stroke only has the screw that controls the movement of the barrel, no idle stop. All of the others though have both screws. Even an old Fox 40 I have. All of the idle stop screws had a spring on them, all of the barrel screws, screwed down tight, no adjustment.

Don

I appreciate all the help on this. This is what I have found out. On the ST that I have, the idle stop screw that comes down on the top side of the carb is really not needed since the radio equipment that we are using these days will control the idle and stopping of the engine reliably. With the screw out, the barrel will not move laterally because there is a horizontal screw that is in place coming into the side of the carb to keep the barrel in place. I flew the plane today without the screw in place, the motor ran perfectly for four, seven minute flights. It was a good day. Thanks everyone for your input.