Carb slide - vacuum piston modifications
 

Hello. I recently bought a jet kit from this company 6sigma racing. Along with some jets and needle shims, they sent me a #59 (very very small) drill bit to drill out an additional vacuum hole in the carb slide. The theory makes sense - another small hole will change the vacuum effect and allow the slide to move up faster giving faster throttle response. Fine.

I really don't have a problem with the bike's throttle response. It's pretty quick around town, and of course it's only a 250. But would I mind if it had a little more pep off the line? Not really, no.

The only thing that bugs me is the disclaimer that accompanied the instructions for how to do it, which read something like, "This modification could have serious adverse effects on the drivability of your motorcycle". Also, most people on other forums that I've read say not to do it. But in none of these forums were they discussing GZ250's.

So I'm wondering if anybody has ever done this modification to a GZ250 and, if so, what were the effects?

Not necessary. This is a modification that you would want to do if you were a high-end carb tuner for a high-end motorcycle. Neither you or the GZ are either of those things. (And that's not meant as a slight at all.)

These bikes are very simple and can be tuned without ordering a specific jet kit, even.

What you get from jet kit manufacturers is a generic kit filled with lots of things that you don't need. Notice all of the various jets and shims that won't even fit your bike? The #59 drill bit falls into that category.

Just adjust your main, the needle, and then dial in your pilot jet and you're good to go.
Don't worry about the other stuff.

:)

I hope you didn't spend a lot of $ on a kit you didn't really need and were advised not to buy. You state that the bike runs well so why spend the $.

Actually the 6sigma kit only had parts that either fit or were specific to the GZ. Not too expensive either ($50 including shipping). I definitely recommend them if you ever need a jet kit for anything.

The reason I jetted the carb wasn't to increase performance, it was only so that I could ditch the huge stock air box for a pod style filter. I'm not really planning on drilling the slide, I was just curious to see if it worked for anybody else.

That said, it does run better now. It takes way less time to warm up from a cold start and it runs cooler than it did. Also, the pod filter allows for some sweet intake noise during acceleration.

the piston modification on a stock motor will make the slider to open to fast and create hesitation.
on a modify engine with a big cam because the low vacum it will make the slider to open at the correct speed

Now I understand. Makes sense now. Carry on and enjoy the ride.

just try it if u want....

but for me....its better to get VM type carb

i just plug FCR37 carb in my stock engine few weeks ago...its the best mod i ever did and couldn't be happier....its big smile on my face when i ride with this one...