From what I gather the pumper is only going to give you better response on the low end, no more peak power just better response. The big bore will (I would think) shift your entire power/torque curve up from 0rpm through redline. Myself I'm leaning towards the 300 kit over the pumper because I'd like some more oomph at cruising speed on the road, offroad I'm not a skilled enough rider to need the extra snap, some more torque would be good just to tractor along. I ride mainly ATV trails so I'm not log hopping all the time and don't need to get the front sky high.

 

If you can only do one right now, my recommendation is to get the big bore, 331cc and dial in your CVK, pull the airbox lid, bump up to a 130 or 132 main and put your N1TC clip on the 3rd or 4th position, make sure you've drilled your vacuum slide port to 7/64ths but I think you've already done that.

Ride and enjoy.

Later, go with the pumper.

Don't get me wrong, I love the pumper carb. And I know there are folks who feel differently, but if I could only do one, and knowing everything I know right now, I'd choose the 331cc first. There's no right or wrong answer, though - I think which one suits you better probably depends on your riding style. I love the low-end grunt the big bore gives. Of course, that low-end grunt really comes alive with the pumper, not that it's bad with the CVK, the CVK works well when dialed in. That's why I say don't exclude the pumper, get the big bore now, but work on the pumper when the opportunity presents itself.

 

If forced to choose between the two, I think the331 will net you the best results.

I chose the pumper first for my ownreasons.

1. I don't even have 10,000 miles on the original jug, so I want to get my money's worth outof that first.
2. I(personally) have no burning desire to add torque and horse power right awaybecause I'mstillenjoying the mods I've done so far.
3. No desire to do 'brain surgery'right away.

With all being equal though,I think you get more 'bang for the buck' from the 331. I can easily see that happening next season.

 

I went with the pumper first because it is quite a bit cheaper than the 331 upgrade and I want to get at least some use out of the 250 cylinder. Now that Bill B. is doing thesleeve on the 250 cylinder, I will probably go that route after this riding season gets over. I think Marty went this route and he sounded happy with the sleeve and parts being around $450.

 

I started with a KLX300 and a buddy has a 250both had/have dialed in CVK's. With my 300 theFCR35 was a dramatic difference over my CVK. After riding the 250 I would say an increase in CC'S is a must first if you could only do just one. I have not ridden a 250 with any of the pumpers. Thepumpers improvementis noticedthe most I think riding off road hammering up hills and negotiating through and over obstacles. You don't really have more power but the responsiveness and acceleration sometimes makes you think you have more power and enables you to negotiate difficult trails easier. My FCR35was the best "mod" I have done to my KLX and I've done a few. I must say that professional suspension set up is also very high on the list as to how the KLX handles on serious off road trails.

 

Iowaguy I am not speaking from experiance, but I thought I read somewhere that a 300 with a properly setup pumper carb will out perform a 331 with a properly setup stock carb.

 

Don't you mean 'Brian Surgery'??

 

I think that was a compliment, right?

 

Something like that. Can't go that route because I'd have to immediately buy a KTMonce I finished...'that's the rules'[8D]