I was looking at my S&S E carb and noticed that the venturi is actually pretty small. About 1.55" Even though at the mount it is as stated at 1.875" I was wondering if anyone has bored their carb and how much? And what kind of changes did it make throughout the rpm range. More or less HP/TQ at the bottom and also more or less at the top. Also did it make a difference in how fast the motor ramps? I know if I do it, it will need re jetting. My motor is a 98 evo and very well built. A G series carb would be too big but I would like to get a little more out of the motor if I can. Thanx...

 

I would suggest bigger hole = less torque, more hp. (And a good call on the 'G'. Way too much carb IMO.)

 

a 42MM mikuni with out the acc pump connected would be very noticeable

 

Hey John, is that bore on the 42 mik straight through or does it have a tapered throat like the S$S?

 

MM fuel injection would wake that puppy up

I crack myself up LOL

Dave

 

Do some reading on carb venturi and velocity

 

Thanx John. I googled "Principles of Carb Venturi and Velocity" Definitely a clear cut decision not to bore the S&S. By doing that I would be decreasing the size of the venturi which will decrease the velocity of the air flowing through it which will actually cause it to draw less fuel as well. My air fuel ratio would probably be hard to get right at that point. So I think I'll do a little more research on the Mik 42. Thanx again...

 

Hold on Mr Impatient, boring a S&S does work and run one, will pass on what I gathered from some heavy hitters. Velocity with compression and flowing ports can also cause bad street manners, a larger bore will slow down velocity and promote better street manners. You was mentioning less velocity will starve the top side but a T jet with the slower air takes over on the top side to cover AFR's, can have a free flowing carb and get fuel.

A Mikuni is a crisp carb and a great choice but a S&S is known for all out WOT throttle power, the throat bore with T jet lets you use the small jet down low, the large jet can be lowered for more of a mid range and the T jet blends in and takes over on the top side so velocity isn't needed as much to pull the fuel like a 2 jet set up.

My Super G is bored with the set up mentioned and street manors are like a stock engine and WOT throttle is as expected and smooth a silk. Go to Zippers website and look up Zippers T jet install info and good reading material for S&S carb operation

 

S&S with a thunder Jet is the setup I currently have. Jets are .0295/74 w/95 t-jet and a main air bleed jet of 160. I guess I'll have to do more research and reading.... Thanx....

 

The discussion on carb throat sizes is an interesting one. I have a bone stock S&S 107" engine with G carb, but their later 111" engine comes with an E! So we cannot safely assume that there is only one solution to performance.