EVO 4 Stroke Carb Spring

[mcman56]

Has anyone experimented with these?  Are the springs intended for higher elevations weaker?  Can you get quicker response at sea level or do you just end up with pop and stall? 

 

https://betausa.com/evo-4-stroke-carb-spring/

 

 

[konrad]

I'll preface these remarks by stating that I have never touched a Beta 4T carb.  But I do have some experience tuning constant velocity (CV) carbs.  

The thing about CV carbs is that no matter what rate the rider opens the butterfly throttle, the vacuum-operated slide only opens in response to engine demand.  This is great because the manufacturer can fit a large throttle bore, and the bike is still easily driveable by a ham-fisted rider.

If you make the spring that controls the diaphragm weaker, the throttle connection will become more direct.  Look at the design equations for springs to see the variables you have to work with.  The simplest solution is just to replicate the standard spring with a greater number of turns (but you have to be careful about coil bind so the slide can still open fully).  Alternatively, you can wind the spring from a thinner diameter wire.   

I have bought spring steel wire from McMaster-Carr  https://www.mcmaster.com/products/spring-wire/steel-1~/  but I expect there are other fine sources.