I just bought a 2014 KLX250S with the big bore kit (330). It had a jet kit installed when the big bore was added. It has an FMF Q4 exhaust and I just noticed yesterday the top of the air filter box has been removed. When I get up above third gear it starts hesitating when trying to get above 7000 rpm. Since the airbox is open and it has an aftermarket exhaust, am I correct in thinking it needs richer jetting???? Any suggestions.

 

I'm running lidless 331 with full FMF Q4 and if I remember correctly I ended up running a DJ148 with the the clip super glued to the top notch of the DJ needle.. I'm about 400' asl and am also running a #40 pilot.

Compared to stock, she's a beast even with the CVK carb. One day I'll grow up and switch over to a pumper carb, but the fraction of a second lag and windup of the CVK gives me a little time to correct a whiskey throttle before she bites me.

I think the largest jet in the DJ kit may be a DJ132... maybe even the DJ128, but definitely not enough jet to go full exhaust and lidless in the stock kit.

Only way to know what you have is to pull the carb and see what's in there.

 

I used the duct tape trick to close off part of the open air box and low and behold, it reved up past 7K quite nicely. With all that air going into the carb it did not have enough gas to keep going. Thanks for the help and suggestions.

 

Sweet... so you either need a lid (ebay?) or a few jets to play with.. Jets-R-Us has a good selection if you know what brand kit was installed. Dynojet is pretty common, but there are other kits out there. I believe the FMF branded jet kit is Dynojet.

With my 331 I've run (400 above sea level):

DJ132 with lid on and no snorkle, clip at the 3rd slot on the DJ kit needle.

DJ146 or DJ148 lidless with the clip on the #1 slot and washers superglued on top. (Don't remember which one is in there now.. I think its the DJ148)


The lidless setup and 14/47 gearing is working very well for me so far. I only have about 350 miles on my big bore as I only use the KLX on trails and it has been too hot this summer to want to get out in the woods.

 

In case any wonders why I did not chime in, we already have a few members attempting a lidless setup on a "bought used" KLX.. The unknowns from a previous owner have to be investigated and rectified before the lidless recipe (like Abramsgunners) can be used. Needle, slide lift port dimension, pilot jet, slide spring, main jet, etc, all must be identified and verified useable - or fixed, or replaced.. Then an accurate list of what needs to be bought can be made. Then comes the "carb session" , with all the problems/faults a newbie can create during it...

If gorgeguy can get his bike running better by closing off the airflow to the engine, he is in good shape for now.. If he wants to unleash his monster with a lidless setup, he must be willing to become "CVK knowledgeable" and begin checking his carb's components..