Baja..

the LSN = Low Speed needle / Bottom Mixture / Idle Mixture (Take your pick)

AT IDLE : It is a Needle and seat that restricts the amount of fuel that is atomised by the air rushing in through the Carburettor and is draw by the venturi effect and some type of fuel pressure method.

On a carby engine we control the amount of fuel to air by managing the amount of fuel. On a modern real car, we turn things around and manage the AIR and the injectors maintain the constant.

One concept to get your head around with a Nitro engine is that the Low Speed needle is bound to the throttle cylnder. If you add more idle, it usually opens up the bottom needle allowing more fuel so that there is a relationship between the throttle opening and the bottom needle (idle mixture).

Once you are past a certain point on the throttle the LSN needle is completely withdrawn and maximum fuel flow takes effect. The governing factor to this is, the venturi or vacuum created by the engine exhausting after comubustion. This in addition to fuel pressure manages the overall mixture.

Before we enter a TOP NEEDLE discussion, just think of it as two taps on the fuel line in series. The top is the maximum fuel flow, the bottom needle is the mixture at IDLE.

If the bottom needle mixture is too rich, then the car will be boggy. Too lean and it will over rev and create a prepetual problem as the engine revs higher draws more air in and leans the mixture to the point of over heating.

This can work in reverse with a false idle, where there is too much air and the LSN needle floods with too much fuel, this will drop your revs. In fact the idle is too high allowing too much air and when you full throttle and finally clear your engine of excess fuel it will have a HIGH REVVING idle.

All this said and done, a NEW engine that is not run in will misbehave regardless. As is warms up it becomes looser and it's too difficult to tune until it's run-in properly.

Additional Notes:

If the HIGH idle happened suddenly with no change.

• You have an AIR leak somewhere. (Too much air)
• There's something restricting the fuel. (Not enough Fuel - Blocked needles, too lean on the top, hole in fuel line)
• Low Fuel pressure ( Poor sealing of exhaust manifolds or hole in the pressure line)
• There's something restricting the closing of the throttle cylinder (High idle - Disconnect servo and see if you can close the throlle more - adjust idle screw)
• Mixture screws have O-rings for a good seal and if these wear the mixture screws can unwind (Mixture needle winding in itself)
• Your servo's need to have their end points set correctly so that the servo does pull on your carby at full throttle and allows it to close enturely. (Radio alignment)

EVERYONE should use a rubber band just strong enough to pull a throttle closed. your servos are strong enough to overcome this opposong force. (Springs BREAK!)