Topic: Rejet for pods but plugs are black

[terrytwotunas]

Im trying to understand why i need to rejet to allow more fuel to my system after adding pods when black plugs are supposed to mean your mixture is too rich.

[900WOT]

Im trying to understand why i need to rejet to allow more fuel to my system after adding pods when black plugs are supposed to mean your mixture is too rich.

Jets are a factor but needle position is a factor as well.

You could have a stuck float, etc.

[BomberMann650]

What type of bike and which carbs?

[PeWe]

Floats that will cause fuel floading at low rpm is one reason why have so many black velvet colored plugs in a box. pitch black within a few minutes. If carbs are super lean upon that not visible until floats  with fuel level in carbs are correct

[TwoTired]

The cylinder sucks air and creates negative pressure as the piston falls during the intake stroke.

This pressure is equalized by the inrush of air through the intake duct system.  The duct entrance is at outside atmospheric pressure.

The carb throat is in that pathway and experiences the negative pressure midway through the equalization process.  The negative pressure the carb throat experiences is presented to the various fuel jets in the carb.  The opposite side of the fuel jet is presented with outside atmospheric pressure by the carb vents, which pushes the fuel through the jet due to differential pressure.

Imagine the carb as being halfway between the cylinder and the inlet.  For explanation sake, let's say the the negative pressure is also halfway between outside atmospheric, and the deepest negative pressure that appears at the cylinder intake valve.  Say 1/2 atmospheric.
This determines the force pushing the fuel through a given fuel jet orifice size, and the volume it will pass.

Pods, shorten the duct, and also allow faster equalization of inrushing air toward the intake valve position.  This effectively moves the carb closer the the air entrance and the outside atmospheric source.   The effect is that the carb throat experiences less differential pressure than it had under the stock arrangement.  Remove one third of the duct and the carb now experience 1/3 of the negative pressure from the cylinder's falling piston.  Less differential pressure is then presented to the fuel jets equate to less flow/volume of fluid that can pass though original jet sizes than before with the original duct arrangement.  There is NOT equivalently "more air", as the engine cylinder falling piston still displaces the same amount of air to create the same negative pressure as before the air duct was modified.  To compensate and restore the air/fuel mixture to the same levels as before the mod, the fuel jet orifices need to be enlarged to restore the same volume of fuel as was was present before the duct change that occurred with the pod modification.

Simple, eh?  Aren't you glad you asked?

Cheers,

P.S. You are aware there are three fuel delivery path restrictors in the carb, right?
 

[flybox1]

were they black BEFORE you put pods on?

[BRG-BIRD]

The cylinder sucks air and creates negative pressure as the piston falls during the intake stroke.

This pressure is equalized by the inrush of air through the intake duct system.  The duct entrance is at outside atmospheric pressure.

The carb throat is in that pathway and experiences the negative pressure midway through the equalization process.  The negative pressure the carb throat experiences is presented to the various fuel jets in the carb.  The opposite side of the fuel jet is presented with outside atmospheric pressure by the carb vents, which pushes the fuel through the jet due to differential pressure.

Imagine the carb as being halfway between the cylinder and the inlet.  For explanation sake, let's say the the negative pressure is also halfway between outside atmospheric, and the deepest negative pressure that appears at the cylinder intake valve.  Say 1/2 atmospheric.
This determines the force pushing the fuel through a given fuel jet orifice size, and the volume it will pass.

Pods, shorten the duct, and also allow faster equalization of inrushing air toward the intake valve position.  This effectively moves the carb closer the the air entrance and the outside atmospheric source.   The effect is that the carb throat experiences less differential pressure than it had under the stock arrangement.  Remove one third of the duct and the carb now experience 1/3 of the negative pressure from the cylinder's falling piston.  Less differential pressure is then presented to the fuel jets equate to less flow/volume of fluid that can pass though original jet sizes than before with the original duct arrangement.  There is NOT equivalently "more air", as the engine cylinder falling piston still displaces the same amount of air to create the same negative pressure as before the air duct was modified.  To compensate and restore the air/fuel mixture to the same levels as before the mod, the fuel jet orifices need to be enlarged to restore the same volume of fuel as was was present before the duct change that occurred with the pod modification.

Simple, eh?  Aren't you glad you asked?

Cheers,

P.S. You are aware there are three fuel delivery path restrictors in the carb, right?
 

I have never done pods before yet understand they require jetting and this post explains it in a way even I can understand, thank you.