Pumper Carb vs. Dynojet CV carb on 250 pot
 

Hi guys

I did a search, and although I have found explanations on CV vs Pumper, I have not found anything specifically dealing with my question.

On a stock 250cc pot, how much of a difference is there between a properly dynojeted stock CV carb (which I currently have on my bike) and a pumper carb (be it a Bill Blue TM33/34, stock TM36 flat side, or 35mm FCR)?


I ask because after riding Fletcher's KLX351 with pumper, I have decided that the power-up is not significant enough for me to justify getting my own bigbore kit (before you crucify me, it's because I would have to pay someone to fit it for me which would effectively double the cost of the upgrade for me, it's not because the power-up is insignificant), but the pumper card possibly is justifyable. That being said, in the very short ride I had, I am not 100% sure how much of the extra pick-up was the carb and how much was the bigger bore.

So on my stock 250 bore with my currently openned up airbox + slipon, is there really that big a difference in performance? With the enlarged hole in the slide, the CV does react a bit quicker than in stock form, and although it will not ever be as direct ast the pumper carb, it is not quite as "elastic" as the carb in stock form.

I am also wondering how much of a difference the type of terrain and riding you do affects the importnace of quick throttle response. On asphalt/tar where the rear wheel is not going to break traction as easily, I am not sure the pumper is that big an advantage. But on dirt, when you want to break traction quickly, or at least get it to bite hard, the pumper will no doubt be more of an advantage. But by the same token the smoother onset of power from the CV could be an advantage where you don't want to break traction but instead rely on the billy-goat grunt of the engine to put the power down to the ground.

Just to clarify, I have no doubt the pumper is superior, I am just trying to guage how superior it is as this will help me justifying spending the money on one or not.

Thanks in advance for your help.

I wouldn't even bother with a pumper on a 250.. I really doubt the gains are worth the $300 or so you'd be spending on the carb. Probably better off with a $30 vortex throttle. I guarantee the gains you saw on that 351 bike were 98% bigbore, 2% pumper!

Put $250 with it and get the big bore!! And you wouldn't need to have a shop do it unless you've never turned a wrench in your life... In which case you shouldn't have a dirt bike :)

It's the displacement, not the carb replacement, that is the reason for the increased power.

The carb's benefit is mostly lack of hesitation.

A properly jetted carb, be it pumper or CVK wont add power, they just deliverer the engine power differently.... i.e. a pumper is snappier as the power is delivered straight away as the throttle lifts the slide.... the CVK is smoother as it uses engine vacuum to lift the slide but takes a smidge longer to hit that power.

I intend to go big bore eventually but was planning to do this first before the carb upgrade but got a good deal on the carb which is why it came first. If your never going big bore just stick with the CVK (even though I recon the TM36 pumper has helped heaps out on the trails).

The TM 33/34 that is for sale here seems like a good buy though…. So if you were planning to big bore eventually I would get it... even if you don’t install it until the big bore.

Over here pot has whole different meaning, but I get it now. Have you ever sat down and read through the service manual. It's really quite easy to do, fit a new pot that is.There may even be some videos on the subject. There is a copy of the 09 service manual right here on this website. It's the same procedure for any year though. You might just read through just for grins and see if you couldn't DIY.

One small benifit to the pumper is any starting problems you may have go away.

IMO, there is nothing wrong with a well jetted CV carb.

+1 on that. I've ridden a fair bit with Neilaction (300cc and pumper) and it's the extra 50cc that makes all the difference IMHO. I'll be upping to 300cc as soon as I get my arse in gear and a full 6 hours sleep.:D

Funny, only people who do not have direct lift carb on their bike seem to be in the opinion that CV carb is just as good.

While dyno plots show that bike makes more peak HP with pumper vs. the stock CV. And dyno plots don't even show the drastic difference in throttle response.
Oh well, I've used both kinds back-to-back and all other things being equal there is a big difference. But I'm sure others know better.

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Mikko

I never said it was just as good, I said bang for your buck the big bore is the best mod for power.