Nitromethane


/end thread

 

I'm guilty of thinking a direct lift carb will not be a big benefit to a stock KLX250s...and I've never tried one on this bike. I had one on an XR650, and that bike's power is impressive compared to any non-turbo'd KLX250 variant, but, honestly, I haven't run one on a KLX250, so, I'm guilty of assumption without experience.

 

As CousinLarry pretty much says, it's not so much that I believe the CV will be as good as the pumper - not at all. I fully expect the pumper to be better. My question is more around whether it is that much better to be able to justify dropping as much as I did on the slip-on + dynojet kit for the pumper - I don't know if there will be as much of a performance hike for the same money.

 

Good debate here. Where's the proof? Before & after testing of carbs alone? On 250s or big bore? Finn - where are the dyno plots? Who's had a CV then pumper on the same setup and wants to go back, or v/v? Who's tried both and wouldn't have the other? Why? I'm hearing ++ on starting & acceleration for a pumper with mixed opinions on torque and hp.

Winter's here and as a new owner of a clean stock '06 (clearly the best year) doing a few mods now (airbox, DynoJet kit, HMF slipon & "opening her up", pegs, skid plate, Guts tall seat foam ), maintenance, and hopefully some suspension before spring riding (raising link? rear spring? forks for 6' 205lb riding tech trails, open desert and tar). Plan to ride as a 250 next summer then may go to a BB big bore as next winter's project. I think the threads show the 331 can run just fine on CV, but the 351 needs a pumper bump.

what say ya
cheers!

 

Personally i wouldnt go back to the CVK now that im running a pumper.

Also i like to tinker and the pumpers got way more adjustments to fine tune than the CVK carb.

 

IDRIDR, on your question about proof in the form of dyno results, that may be hard to find. I think many go back to Bill Blue's and Bake's dyno results which showed Bill's having more power with a pumper. The problem with that is that the bikes weren't the same. There were notable differences in the exhaust and some other mods that give Bill's bike the edge. That's not to say that the pumper didn't add power, it's just not conclusive. Also you have to be careful about comparing dyno results from one dyno to another as to max torque and horsepower. A dyno is more valuable in showing how much of a power increase/decrease occurs on a given engine with specific mods...on the same dyno.

Also a dyno won't really show the engine response as much as real world operation...will it? I don't think dyno runs are performed with whacking the throttle open and chopping the throttle closed in quick succession like you do when actually riding on a trail...are they? This might be where a pumper, when tuned ideally, could have an advantage. I'm not bashing the pumper, but it's not a priority for me on a KLX. I think one reason the KLX is such a good climber in loose, steep, technical terrain is its unbelieveably smooth power delivery. I don't doubt that a properly set pumper could delivery a quicker, harder response, but I'm not sure that's a one-size-fits-all application. It may depend more on how and where you ride.

I don't think anyone can argue the benefits obtained by more displacement, but how that additional power is delivered can be somewhat preferential. Those of you who have owned some higher performance race oriented dirt bikes know that more power and/or harder hitting power delivery isn't always the bottom line for off roading. Street bikes usually don't have as big an issue with this, but the sketchy traction conditions for dirt bikes can make this more important. The KLX is hardly suffering from being overpowered, but just a little more aggressive power delivery can be a plus or minus depending on conditions or the rider.

 

What? Where did you find this? I have never heard anyone say that before. There are lots of people running stock carbs with 351 big bores and they all seem to work just fine.

There really isn't much difference between a 331 and a 351, we are literally talking a little over 1 cubic inch of displacement. Get the jetting right and these little carbs can do more than you think.

 

Read this on one of the threads here - it was likely one from several years ago. I made a note of the comment, but didn't copy the thread or link. I understood it as a "must" but it was probably just opinion if lots of ya are running 351 with stock carb.

 

TNC - that's exactly why I asked for the proof. I've looked all over and haven't found it so let's see it!

Good question on dyno tests. Usually I see a smooth torque ramping over the rpm range, but why couldn't the dyno be used to demonstrate quicker response?

 

I've read that one of the virtues of a CV carb is that it's relatively insensitive to changes in altitude, which could be an advantage if you live in a mountainous area. I live at 1600' and ride up to Carson Pass at over 8000' and don't experience funky carbeuration issues now that the jetting is dialed in. (can't compare to a pumper on that count, though)