Horse power difference between carbs

[Up north rider]

I’m thinking about changing some stuff up when the snow is on the ground. I’m currently running 28pwk’s on my 421 assassin 2. I have an old set of 33’s on the shelf that I want to put on for the extra power but I’ve been watching videos on people running big carbs like 38’s. The power looks unreal. What kind of horsepower power difference between these carb are there? I’m currently running 100ll 

[locogato11283]

You won't see any benefit, and possibly loss, from running big carbs.

Until you're into the 10mm+ motors, there's no upside to the big carbs.

Stick with the 28s until you build something bigger.

[Up north rider]

Would you consider the 33’s to be big as well? 
So basically the only thing I’ll notice is my tank will empty quicker? 

[locogato11283]

4 minutes ago, Up north rider said:

Would you consider the 33’s to be big as well? 
So basically the only thing I’ll notice is my tank will empty quicker? 

I doubt you will feel any noticeable performance gains from the 33s.

You will gain power on top but your bottom end will likely suffer.

I'd stick with the 28s. 

[Up north rider]

I appreciate the input! What would you do then to make this machine just bit more dialed? I could put k&n over the foam filters, or pro mod the trans. Just spitballing 

[locogato11283]

14 minutes ago, Up north rider said:

I appreciate the input! What would you do then to make this machine just bit more dialed? I could put k&n over the foam filters, or pro mod the trans. Just spitballing 

Pro mod will help with the shifting. What pipes are you running?

[Up north rider]

CPI’s. I’m not quite sure if there small or big bore 

[locogato11283]

35 minutes ago, Up north rider said:

CPI’s. I’m not quite sure if there small or big bore 

Most likely small bore. That's a good pipe. No change needed there.

[Up north rider]

Going from 23cc domes on pump gas to 21cc on 100ll was a nice bump. Especially in the midrange. Think the cotton filters are good for a horse or two? 

[SKEETER]

Who ported the cyls, and what type?

[Up north rider]

The cylinders are as cast. They’re driveline’s second gen assassin cylinders. They told me all the porting they would do on the first ones are now cast in. 

[locogato11283]

6 minutes ago, Up north rider said:

The cylinders are as cast. They’re driveline’s second gen assassin cylinders. They told me all the porting they would do on the first ones are now cast in. 

There's not really much you can do then.

What about suspension? What are you running?

[Up north rider]

Lone star a arms with fox float 3 shocks. 
 Rpm axle with reworked factory rear shock. 
 

[SKEETER]

Have you talked to Bill and seen what his opinion would be for more usable HP?     28s to 33s will get you a few extra hp , but not worth it.    What type of riding you do 90% time is better question 

[Up north rider]

We go fairly long distances sometimes. We may go 40-50 miles at a time. Some sand And of course just backyard drag, wheelies whatever else. Kind of everything. 

Edited December 30, 2025 by Up north rider