Recommended Carbs

[Rubbersalt]

Carb sizes are relative to the RPM/displacement. So I decided I'll be kind enough to share some information with you guys.


The sizes have been calculated with some of my software. These are intended as close reference points. Actual size need for peak power may very(doubtful ).


Lets start at a 26mm Carb - stock size.

RPM - Carb
7252 - 26mm
7554 - 27mm
7854 - 28mm
8153 - 29mm
8449 - 30mm
8742 - 31mm
9033 - 32mm
9321 - 33mm
9608 - 34mm
9893 - 35mm
10176 - 36mm
10457 - 37mm
10736 - 38mm
11014 - 39mm
11289 - 40mm
11562 - 41mm

I don't advice using a carb that is going to flow more than your port work. Your engine will struggle to pull enough gas at the top end, and your bottom end will suck. An undersized carb is better than an over sized. The undersize will give more torque, just not as much top end.

Flat slide carbs are more efficient at pulling gas from the jets. This allows for better atomization of the mixture. They also flow better(on the flow bench atleast)

 

[Blaner]

hey very nice, have so green eggs and ham

 

[Luni]

But in theory, assuming you have a powerband you can hold it to, wouldnt more airflow always equal more usable power? Lets assume the engine can take 9500 rpm, and you can get it up there all the time, bike one that revs out at 8k rpm will always be slower than bike 2 that revs out at 9500 rpm.

Transmissions are a torque multiplier, so even though the smaller carb might increase torque, being able to hold it longer in the band makes for more power.

So, Im thinking of going to a 34mm pj. Its interesting to see what it does for my top end. I guess Ill just have to install it and see what it does to my bottom end. The carb will be free, so thats the only reason why Im gonna use it.

 

[Surfrjag]

Are these figured for a stock stroke and bore?

 

[Rubbersalt]

Yeah, these are for the stock bore and stroke.

More air flow does not mean more air will flow. With carbs, there is a vacuum on the jets. If you have to much air flow, there wont be enough of a vacuum.

With a small carb, there will be a monster of a vacuum. At high RPMs the carb is choking the engine. At low RPMs the velocity of the air mixture is high. This causes more air/fuel to flow into the cylinder.