I'll start a separate thread regarding testing the 3 carbs in timed 0-60 sprints. Not only at 250cc, but later after doing the cam mod, and then again after installing my 331cc kit. (with a few other variations along the way perhaps)

The 40mm carb tested with a best 0-60 of 6.56 sec

Today the 36mm carb showed a best 0-60 of 6.35 sec with a 6.5 sec additional effort.

Very very close. Riding around today more with the 36 still in place, it obviously has more low end torque than the 40, but don't think the 40 is making the engine pipey or lacking low end because there's still plenty of low end with the 40mm carb. If I were going to sell one of the two I'd probably opt to keep the 40 because of other mods planned down road that might let the larger carb produce more power than the 36 would. It'd be hard to find a buyer for the 36 over here, but I may put it f/s online and see what happens..

For now it'd seem that if you weren't ever going to increase your engine size beyond 250cc, and you weren't going to do the cam mod, then the 36mm carb would be the better choice-but just by the thinnest of margins. I think the cam mod is next for me after I test the 34CVK, so there's more info to come.

If you have a bigger bore or are planning to go that route, then until the 40 gets tested with 300 or more cc, then which carb to go with isn't so clear. Some might say the very close 0-60 times between the two carbs could prove the valves/port etc won't support enough flow for the bigger carb, but I'd say that's only if you're a pessimist. Until the 40 is tried with bigger cc's it'd just be a uneducated guess.

I still need to test the 36mm with the vertical insert removed from the engine side of its throat. - Just to see if the insert makes a difference at all. Then test the CVK34 just to see how it does-since BB reportedly makes max power on his bike with the 33mm carb bored to 34. Yes the CVK still has the butterfly in the way, but it's worth a test since I'll have to remove the 34 to take the vertical insert out.

 

The valves and ports are flowing nowhere near their potential with those cams. Skip the cam mod. Do it properly, and put a set of performance cams in there.

 

Well, call me a pessimist, Richard...LOL!

Look...nothing wrong with playing with huge carbs and trying extreme components to see what happens if money or access is no issue, but ZW is right in that you'd be ahead in doing cams with the 34 or 36. Physics is physics, and there's a reason you don't always see huge carbs on racing bikes of certain displacement ranges...much less our wimpy KLX. Also, I'm aware that your bike seems more used in a street-style setup than a dirtbike. In a dirt environment where lugging, on/off throttle response, and a wide array of throttle range is encountered, a huge carb may not be the best alternative.

 

There always has to be the pioneer - the one that bucked prevailing wisdom and dogma and provided the foundation for a new paradigm. If only Richard had a Dyno, he could provide irrefutable data to back up his findings. It is ashamed that no one else is likely to procure 2 additional carbs, set them up as per Richards findings, and dyno test them, and ride them, for an assessment.

Richards tests, and his tests to come, are providing truly unique information. What a stroke of luck that he is here, in KF, advancing our knowledge.

But, for the 351 crowd especially, you gotta wonder about the 40..

 

I need to know what happens when he does the MCM and puts a TM36 on it. I hope it is a maniacal race bike like TRQ hit that maintains to cutoff - all using Richards' tuning on the TM36 - jetting, accelerator pump, needle, and AFR meter verified

 

I need to know his opinion of the differences in performance between a properly setup and AFR verified CVK and his verified setup on the TM36 - after he does the MCM.

 

Wouldn't it be nice to build on Richards' information and end up with a Dyno verified recipe for getting something like 23-25hp for under $500 that then goes directly to 30hp with a BB kit ? I'm talking about carbs, pipes, airbox mods, MCM cam retime, Ignition advance curve mods, all rolled into one big recipe... SWEET!

 

MCM mod does not work well with the big bore kit from what I've read, its been a while and I might be mistaken. Why do the MCM mod with a 250, just to revert back when you do the 351? Put webcams in there like ZW said. A better comparison IMHO would be stock cams vs webcams on the dyno with the 250 jug, I don't recall ever seeing a dyno run confirming power increase.

Further, it is well known that the valves and head needs work to produce anywhere from 2-5 horsepower regardless of cam and carb combo. It needs de-shrouding and larger intake valves and a small clean up of the ports. Not to mention a port match.

 

I haven't found any loss of low speed friendliness with the 40mm carb. There's plenty of low end still for just about any plonking situation you'd run up against. Hard to believe, but the 4mm increase in venturi just hasn't taken much low end away. If anything I thought the 36 still had excess low end available. At least with this 14/48 gearing.

It's not a matter of money being no issue either-I can always sell one of the carbs. Members have spent a couple hundred (or more) on exhaust systems for example that don't add much at all. This is just more foolin' around to see what happens, and giving me something to pass the time with.

Keep in mind quad 40mms are an option for highly tuned 1200cc street bikes.

There's no sense in saying it's too big because it works and works very well. You only notice the difference in low end if you ride the two versions. But just riding around with the 40 it's not like you're wondering what happened to the low end power


I'll go with the cam mod first because my being in the Philippines makes the Webcam option a rather lengthy wait on parts-unless I just bought them outright; which I wouldn't do. If I can get some good before and after vids along with a/f ratios, it'll define what the cam mod does to a/f ratios, and at the same time reveal if the mod works better with larger cc when combined with the 40mm. Because after I am done with the cam mod, it'll be time to put my 331 kit in.


I am going to try and convert to a camera set up that let's me read km/h as I cross a "finish line". Speed is a better indicator of HP changes, and more exact than trying to time it.

 

Richard, don't forget your airbox insert... Now that I have a DJ136 in the bike, I am expecting TRQ gains from the insert, when I get a chance to install it... The DJ specialist told me the CVK is sensitive to inlet velocity and turbulence. With lid off, the insert should result in more volume, less turbulence, and more velocity - PERFECT!