which carb?

[Edman]

So what size carb does the 2012 300 race/electric come with. I assumed a 38 but not sure. Thought I would check.

 

[Fred1956]

Edman, some of them have 36 or 38 cast (I think) on the top (maybe) to be sure take the carb out and measure ID of the engine side throat

 

[Edman]

So what would the difference be in performance wise between the two sizes?

 

[Jakobi]

Not a whole lot in the grand scheme of things. A smaller body will give more instant response in low rpm. A larger one takes a bit more to really get flowing and will favour top end.

The fueling requirements do change though as the engine is essentially an air pump pulling fuel through the carb. Pulling the same amount of air through a smaller opening will increase velocity and as such pull more fuel with it, thus requiring smaller jets to supply the engine with the same amount of fuel.

 

[Fred1956]

So what size carb does the 2012 300 race/electric come with. I assumed a 38 but not sure. Thought I would check.

So what would the difference be in performance wise between the two sizes?

38mm would flow more air so would be better at top end, 36mm is a 'bottom end' carb (at least compared to the 38). RB designs inserts a 'wing' in the center to effectively 1/2 the carb size (creating an 18 or 19mm carb for the bottom end but at full throttle opening you still have the bigger size. The smaller carb (on the same engine size) will increase the vacuum signal across the jets thus pulling fuel harder & requiring leaner jetting. Have to find a balance to be happy. Hope that makes sense