I have an 09 KLX250s, the engine is stock. I want to start upgrading to get more pep out of it. My question is, is the performance better with a tuned TM36-68 or a jetted and tuned stock carb.

 

From all the research and questioning I've done, your answer is yes and possibly no.

Yes the TM36 gives more responsive performance since you have direct control over the slide versus a vacuum controlled slide and butterfly of the CVK.

Possibly no, it is possible the CVK when well jetted may give similar horsepower figures. I don't know that for sure. I think the TM does better, but I forget.

Key point is that quicker response will make the bike feel and perform better since it is more immediate. Even if power was equal it would perform and feel better in the on/off/on throttle use on the road and off.

I know others here may actually have some dyno results between the two.

I will also say I am doing the 36 because of the better throttle response and historically (aka when I was much younger and flat tracking) it seems most bikes can gain horsepower with a 2mm larger carb. Our bikes seemed to stair step, the 125/175 going from 30mm to 32mm, 260 going from 32 to 34, and the one friend's TM400 actually went further gonzo going from 34 to 38.

But a well jetted CVK is WAY BETTER than the stock one. Mine is decent, I just have to try the 36 - the adventure. Did the same doing the Marcelino Cam Timing Mod... just wish the carb was free too.

 

I think your right about the difference not being noticeable on a dyno but the performance increase with having an accelerator pump would be. I've been leaning toward the TM carb, just haven't bit the bullet yet and ordered it. I need to do something, the bike runs good and has decent power, it just lacks the throttle response I feel it needs. Sometimes you need a quick brap of the throttle to pull the front end up for a log, rock, or a rut, and the bike just doesn't have it.

Did you feel the cam mod worth doing?

 

Seems to me that a dyno operator should add to the normal steady state power/torque measurements a transient power analysis run automatically by the machine.

 

On he MCM, I did it before I did a lot with the bike. I know from what I learned some years back that the change made sense and should bolster mid-range power. I also knew that it might not have same peak performance, but I'm not up there all that often and it didn't really hurt much if at all.

I don't know that it's just the accelerator pump since that only works in the first 1/4 throttle. It is more that the slide is direct control versus a slide that has to be sucked up ( he said sucked up! ).

Having played around and ridden a trials bike most of my lofting the front wheel is technique versus raw throttle. I used to be able to pull about a 6-10" dead engine wheelie on my M27 Sherpa T as well as the TM125 while coasting. Weight to front then back and yank. With a bit of throttle it is really easy to get some air when needed. Takes a slight bit of technique on a 4 stroke versus 2 stroke, twist throttle, slight hesitation then pull. That was the difference when riding a TL125 Honda versus the Sherpa T. On the two stroke it was throttle and pull simultaneously.

 

I'm not real familiar with all these mods, but if the TM carb you mention is a flat-slide type it may not be the best choice over the stock CV variety when your riding involves a lot of altitude change.

 

Usually when you update to a flat slide carb, one adds a device on the fuel screw that has a T handle that is easily adjustable (quite different from the stock carb). Once that is done, changing the fuel ratio is not such a big deal when you go to different elevations.
I don't usually change the main jet & only use the adjuster, running from 1-11K ft. If you were racing, that would be another situation, but you wouldn't be doing that on the KLX.

 

The accelerator pump gives so much better throttle response,it's like having 10 more hp. It's not HP, it's throttle response that's changed.

A dyno run measure max hp at full throttle, not throttle response. In fact, the accelerator pump will not even be functional for 90% plus percent of the dyno run, because it only operates as the throttle is being turned.

The TM makes a huge difference. The change is on the order of the big bore kit. It's not quite that difference, but it's not far off. Re-jetting is noticeable, but it really doesn't change how you would attack a rocky ledge or get over a log. You can ride the bike differently with the TM. You can ride it a bit more easily with a rejet.

It's simply not the same.

 

Three words... Dial-A-Jet

I have ridden over about a 5000 foot elevation range and from 18-95° with my 650 with the Dial-A-Jet. I have never done any jet changing on it even after doing a cut air box cover to make it a bit bigger opening while covering the filter a bit still, a big bore 102mm piston, and a full exhaust. The Dial-A-Jet does the job. Read up on it.

I have used the DAJ for about 17 years with the 650, just installed it on the 250 to smooth out lean spots for smoother power, and had a set on my 86 Nighthawk S to eliminate flat spot in the mid-range as noted in one of the media articles. Seems they work well for ATV and Snowmobile use to compensate for altitude change over a fairly wide range. DirtBike! found they worked well and the tricker remote adjustable version, the Intelajet, was used in their 2014 KTM300 modifications. Fine tuning can be done or, in my case, let the system work to lean out or richen mix based on design without further adjustment.

My brother did the jetting changes on his KLX and rode it for a while. I got him a Dial-A-Jet which he installed. Said it improved the power delivery, smoother and better in the mid-range for sure. Suffice it to say, he didn't take it off the bike.

So many people in the motorcycle world ignore it, but it is proven out pretty much in the ATV and Snowmobile markets, which seem to use the same four stroke or two stroke designs used in motorcycles. Most riders who bad mouth it either didn't use it properly or haven't used one at all. I'm thinking actual experience means something as well as proper set up. There is Phil Mickelson, not the golfer, but rather an individual who worked in the snowmobile industry with quite a reputation as I learned, that found the product worked as described and was considered benefical. That isn't some guy like me, that's a person with some serious credentials when he wrote his review and article.

Just sayin' a trick little addition that can compensate like an injector. I'm not too concerned.

 

Really, it's all about money isn't it?
$50-60 and your stock carb can be "Dialed in" for whatever performance mods you want to run ( MCM, slip-on, full exhaust system, lidless, etc )
$300+ for a TM, plus parts for running a forum derived, known working setup..
I don't have first hand experience with a TM on our KLX's - Through our members that do, I get an idea of what it's like - and in my little world, it's nice to run a TM..lol
My throttle response is, no doubt, not as abrupt and as powerful as it would be with a TM - but it is powerful enough to pull a wheelie by just snapping WOT in first gear..