I know it's an older post- but I've ridden both twist & thumb. A twist on an atv (4x4) that is trail ridden is crazy- What I found was this: The handling of a 4x4 and a bike couldn't be more different. You'll spend more time "holding on" when navigating a trail on an atv- because you have 2 wheels combining feedback & deflection to the rider, instead of one wheel on a bike, the bars on an atv are a lot more unstable. If the atv gets out of control, all the rider has to do is let go of the thumb throttle, but can still remain in control of the steering of the atv because he does not have to remove his hand from the bar- whereas on a twist, this is not an option- if you lose control, your hand is still on the throttle, and the only way to remain in control of the vehicle is to continue holding the throttle while also rotating your hand downwards to close the throttle
(simultaneously trying to control the vehicle!)
- and as many of you have experienced, sometimes twisting your palm down, keeping your palm down and remaining in control of the vehicle (especially over rocky terrain) is almost impossible.
With a twist throttle, it's a compound technicality- with a thumb throttle- it's simply not, especially for beginners! How many times have I seen a beginner flip a bike with a twist throttle because they hold on to the twist throttle while losing control- AFV has countless hours dedicated to that alone- none of it would occur with a thumb throttle.
So, I've been there / done that many times. Unless you're riding open pits or live in the mid west / west coast and ride deserts- a twist throttle on a trail ridden atv IMO is eventual suicide. There are many kits available to address this situation. Sometimes just taking some motrin before riding helps the thumb cramp, but after a while, your thumb will toughen up.

 

Thumb throttles never hurt me really not even on 50+ mile trips. I been noticing my right thumb is always numb nowadays tho. I thinks it from riding too much . But I will never stop riding :P

 

I have problems with my arm going numb while riding, but I think it's a carpel tunnel (sp?) thing and not so much the thumb throttle...
I rode my buddy's atv with the palm extender on it and it was pretty neat- I was thinking about picking one of those up.

Also- can you even put hand warmers on a twist throttle? I couldn't live without my headed grips here in mass during the winter!

 

You should be able to put heated grips on a twist throttle. My AC has hand warmers love them. It might be something like Carpel Tunnel that I have too I am noticing my wrist going numb too nowadays. But I cant stop riding....

 

can always adjust the return spring... trim a turn or 2 and then stretch it out a bit

 

wouldn't messing with those springs affect the return to idle or cause it to "float"?

 

shouldnt require too much force to maintain idle ... its not something id do myself ... but its an option

best option is to get one of those extenders so you dont have to deal with the tightness and not doing mods to the bike

 

As for the spring, you can find softer ones on ebay, but you can also mod your own to release some tension by changing where it attaches in the carb.Try googling FCR spring mod. I followed some instructions from a Honda site. Apparently there are some small differences between the FCR used on the TRX and the YFZ, but it showed what I needed to figure out the rest.