is this correct? just saying you put a bigger carb on it takes more fuel right?? soooo from a stk head to a ported head it would have more air sooooo more fuel right???

 

In theory, remember it takes vacum via air speed to pull the fuel up, so if you have a bigger carb or less air speed(velocity) you dont get as much fuel, or something like that. Ok I think I know what I'm talking about but these drugs a kickin my ****, so maybe not, lol Jed

 

Ported head pulls more vacum. Pulls more fuel through the jet so you jet leaner. So I was told at Robertson cycle when checking into it [img]i/expressions/face-icon-small-wink.gif[/img]

 

Its all about keeping the proper mixture. If more air comes in, then more gas needs to be added to keep the ratio correct. And viper is correct, if you go too big on the venturi size, then air velocity drops, and so does torque.

 

Shmee I dont think so at least the way I understand it ...... If you have a "ported" head , and by that I mean one that has been cleaned up not hogged out and not reshaped! You will create a smoother flow more efficient flow... NOT an increase in the volume of air flowed!
SO understanding that your not increasing the volume , just the efficiency ... You arent really feeding any more air through the carb. So when you put a larger carb on then the Velocity drops and the carb doesnt work up to its full potential. Imagine if you will putting a 4 barrel carb on you DS ! Huge Venturies and the ability to flow tons of fuel BUT it would never work cuz that "little" Rotax 650 just cant pump the volume through the carb to make it work reguardless of how well ported the head may be!! Kind of a crazy comparison.
Now if you Increase the ability to pump more through the motor .. Stroker / Big Bore , something to increase CCs then you get the "flow" to warrant a larger carb that will flow more fuel. Add to that a Ported & Polished head and you enhance the performance.

This doesnt mean that some larger carbs out there dont make things better, (the Lectron comes to mind) Some carbs just work better by design!!

 

lets not use the carb, lets just say porting. in all reality it dont realy change much on jetting right...???..

 

The way I understand it the change would be minor in jetting. Nothing that would warrant stepping up jet sizes or anything that drastic.

 

Well said Prozack.