Intake length long or short.

[DEANSFASTWAY]

Ever notice the new KX 125 has like 2 inches from the carbs to the reeds? Why? are they searching for a longer torque spread . I took a 03 KX 125 and pulled the intake off and bolted on a used 03 YZ 125 intake and the carb is now right at the reeds, the bike seems to rev faster and pull harder . All with stock reeds and jets . We had to use a 96 KX 250 air intake boot and a small bell adaptor out of thin tubing and drill the YZ manifold bolts different but it all fits and seems to pull hard. Make me wonder why they put the carb way back there by the shock. I dont have a dyno just SOP but Id like to test.

 

[bclapham]

at last an interesting topic!

Dean- didnt they straighten out the kx125 intake track from 03 to 04, at the same time they gained 1-2HP????

the cool thing you might want to try is look at the rm manifold- it uses the same bolt up as the YZ and is straighter too. as you know, a lot of tuners are shortening the front of the PWK carbs to get them closer- ive done a bit on mine and maybe when i get time i will have a friend put it on the lathe- that stock OEM TMX carb is nice, short and compact- just a shame you cant figure out the needles!

I think we should all throw in $20 each so we can buy you a dyno to test all these wacky projects- some good stuff coming from the Deanster these days, LOL!!!

 

[MikeT]

I'm pretty sure a longer intake tract will produce more low end and rev up a little slower. A short intack tract will rev up quicker and have more top end. Don't quote me but I think that's how it is.

 

[DEANSFASTWAY]

Bruce I tried the Rm intake as well as an older 97 yam 125 intake but they pushed the carb body up next to the shock spring , for 04 kaw also spec out different 2 stage reeds. Ive seen the 04 intakes .The next trial on KX will be inastalling coiled spring into the long intake tract , you know like a spring from the inside of a lower coolant hose on a car. maybe it will add to swirl the mixture maybe not . Yeah I really need a dyno,it seems if youve got a dyno and youre making 1/4 hp more and you can print out a graph youll get more recognition and a right to charge the big buck$ . Thats not really in my constitution though . truth is I like to help out the kid with no money on a 3 year old bike with no graphics kit wearing a hooded sweatshirt at the races but has the guts to turn it up. i like those kind of people, not the prom queens YA KNOW WHAT I MEAN DEANER.

 

[Jaybird]

LOL....When I was a lad, I used to be one of those guys!

My pals laughed at my rats, but I hung! :)
They think I'm too old for this crap now....

There is a place in heaven for guys like you, Deans. You go!

 

[cujet]

Well, the intake tuning is probably 4th order harmonics. Two stroke intake length has to be calculated for a frequency that is double what a 4 stroke at the same RPM would calculate at. Most modern 2 stroke engines have an intake tuning length with a 4th order harmonic close to torque peak. By using a longer intake tract the tuning is biased lower in the RPM range. The thinking might be a wider torque spread at the expense of peak power.

Chris

 

[nephron]

Consider experimenting with reedblock spacers, so you don't have to reconfigure a whole new setup each time.

This means nothing, but Moose makes spacers for the KX500 that turn it into an absolute tractor in terms of low end torque, etc.

Oh yeah, you need to run fuel specific to the intake tract length as has been mentioned here many times before. Longer intake tracts respond well to fuel with higher 10% points. But, like everything, there are exceptions to every thought process.

 

[jaguar]

When you switched reed valves you also went to reeds of a different tension which messed up the idea of experimenting with different intake lengths. The test can only be valid with same stiffness of reeds.