Starts at post #7 here

https://www.kawasakiforums.com/forum...klx250s-41934/

 

Yikes. I could have lived without that.

 

massive powah !!!!!!!

 

Well my stock flywheel with the 3mm extension welded to its nose will be done today or tomorrow and we'll see how well the change works. I think the JB'd 3mm piece did help low end before it fell off-it was idling higher so the timing had been advanced by extending the rotor's nose; but there was no sense at all of it wanting to rev higher.

I'll try it with the 34 CVK just to try and copy Bernie's bike as close as possible

 

It has to be kept in mind that the size of the intake port entrance may be holding the 40mm back. A/f mix coming in through that big carb is forced into an intake port hole that's only 35mm wide x 33mm tall.

I'm going to try and open up and extra stock intake manifold I have to as big as 40mm wide x 36mm tall today to see if it'll take the porting and still remain intact. If not I have an after market intake that's bigger, but it doesn't hold the carb at an angle like the stocker

Once I know I have an intake that will work, I'll plan to get some welding done on the under side of the intake port's flange area when I have the head off to do the 331cc and then be able to open up the port mouth enough to more match the enlarged intake manifold.

It doesn't need a lot of weld under the flange area, and it should be a fairly simple thing to get done once the head's off. With the port's flange being a little distance from the head, there should be no worries of welding heat warping the head etc

Enlarging the port mouth will truly let the 40mm shine if it's ever going to, and the welding part is something others can have done without a lot of difficulty if it all pans out performance-wise.

 

Area computations for the carbs and intake port:



1017 sq mm for the 36mm carb

1256 sq mm for the 40mm carb



1155 sq mm for the stock port

1440 sq mm (max) for the modded intake


Interesting to see the 36mm carb's area is a little bit less than the current area of the intake port's mouth. The port mouth's shape is rounded on all 4 corners quite a bit so the area figures for the port are just approximate.

I may not have to go quite as bit as I thought when modding the stock intake and port if I just want to match the area of the 40mm.

 

Fascinating..

 

I decided now is as good a time as any to dial in the Thunder Products VIP thingy and see how it compares to when this 40mm carb had dual vertical inserts..




These tabs on the engine side were supposed to kind of gouge themselves into the intake's rubber and lock it in place, but that makes it almost impossible to get the thing in there straight unless you install the carb and intake as a unit-which is very hard to do with this 40mm as there's an unused port nipple on the carb poking up right in the way of trying to tighten the RH intake bolt.




Up to half throttle the divider concentrates the fuel/air mix into the lower half of the carb throat increasing velocity. I guess low end power is improved; I wasn't really testing that part of it while checking the a/f ratio. More tests to follow.

So far I've had to lean both the needle and the main jet, even though the instructions say typically you have to richen the idle mix and needle.. But the 40 previously had the dual vertical insert guides and that's the jetting I am coming from.

Limited testing shows the a/f ratio jumping around at WOT. That long divider plate might be upsetting the a/f flow at WOT even though it has 2 holes in it. (looks like I need to de-burr those holes a little doesn't it)

I'll use the a/f meter to get the jetting as close as i can, do some timed sprints, then put the 36mm back on and see how to the two set ups compare. The effective carb size has been reduced some from 40mm due to the plastic V-shaped insert's design-but we'll see what happens with it.



- Not much to find on the internet about people trying the VIP at all. Just the 1 snowmobile magazine's test and that's all I could find..

 

Well this morning's sprint test was interesting..


Starting from what I think was the same aprx point as when testing the 36mm carb, but now from a 17kph roll instead of 12kph; the elapsed time dropped from 5.72 to 5.31/5.35 !

The bike wound through through each gear at WOT much differently as well..hard to describe it-almost like a big bore that wasn't revving super high but covering ground quickly none the less and the shift points just kept popping up without all the racket of higher revving?

TORQUE !

Admittedly my starting kph has changed, and the starting point may be off compared to tests before, but it'd be by just a few feet. I've switched to faster burning 92 octane regualr instead of premium as well.


A .4 sec improvement is still a huge change, and I don't think the 5kph faster starting speed would be the only reason.


Now I'll have to put the 36mm back on and test it tomorrow starting at 17kph. Maybe this VIP thing is boosting mid range torque significantly and will pull the big old 40mm ahead of the 36mm's performance? The only online test for the VIP was on a snowmobile; probably a 2 stroke-so this is kind of uncharted territory that may yield some surprises.

They don't make a VIP for 36mm carbs, but I have one extra that's made for a 38mm. I can narrow the metal piece that splits the carb spigot in half horizontally, but the black plastic holder (designed for the 38) may place the metal divider higher than halfway up..and could be a bugger to try and modify to bring the divider back to the center.

 

The 36mm carb did a 5.12 sprint today. So it's still ahead of the 40mm by .2 sec; but even so, that gives you an idea how well the 40 is working.

.2 sec is roughly how quickly you can clap your hands 2x as fast as you can. It's a very slim difference.

But still enough to declare the 36 still the winner at 250cc