Cr250 05-07 36mm vs 38mm pwk air striker

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12/9/2018 11:54 AM

I have been reading about the air striker swap and I have a good understanding of the fact I need a short body carb and what to do with TPS and power jets.
I understand that the 36mm version (from older kx125s and KTM’s) might come with some benefits to bottom end power which is ideal for me because I will ride hare and hounds / enduro events. What I cannot find is how much the smaller bore carb will effect top end power.
Has anyone tried both the 36 and the 38 back to back? Or offer some advice on a reason for choosing one or the other?

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12/9/2018 3:45 PM

Typically the 36 will give you better low end & throttle response at the expense of some top end and the the 38 will give you better top end pull at the expense of some low end...it appears for your application the 36 would be ideal...

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12/9/2018 5:18 PM

The '05-'07 CR 250s really seem to like the 36mm short body PWK air striker over the 38mm. With or without porting and head mods, the 36mm was better all around. The 38mm wasn't better at ant point on the dyno curve despite trying everything. This was on a bike for the Red Bull straight rhythm section built by a very reputable builder. We were surprised how much better the 36mm was.

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12/10/2018 7:20 AM

DynoDan22 wrote:

The '05-'07 CR 250s really seem to like the 36mm short body PWK air striker over the 38mm. With or without porting and head mods, the 36mm was better all around. The 38mm wasn't better at ant point on the dyno curve despite trying everything. This was on a bike for the Red Bull straight rhythm section built by a very reputable builder. We were surprised how much better the 36mm was.

Have you dyno tested the Keihin 38mm PWK airstriker vs. the Mikuni 38mm TMX ? My butt dyno tells me the Mikuni provides some noticeable gains up top.

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Speak softly and carry a big stick.

12/10/2018 10:35 AM

DynoDan22 wrote:

The '05-'07 CR 250s really seem to like the 36mm short body PWK air striker over the 38mm. With or without porting and head mods, the 36mm was better all around. The 38mm wasn't better at ant point on the dyno curve despite trying everything. This was on a bike for the Red Bull straight rhythm section built by a very reputable builder. We were surprised how much better the 36mm was.

This has been very helpful, thanks.

Can you get hold of jetting specs from this for me, I just need a starting point?

I’m planning on putting my bike on the dyno to compare the mikuni to the pwk, I’ll post up the results afterwards.

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12/10/2018 12:35 PM

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12/10/2018 1:06 PM

Honda H&H: I will ask for the settings he went with.

H4L: The mikuni 38 TMX made little more at peak (like .2hp) more than the PWK AS 38mm but was down on torque from ~4k-9k rpm. The Keihin makes way more torque (both 36 and 38mm) than the Mikuni and carburates more cleanly. The '02-'07's just seems to really like the 36mm AS's. I battled for years with the TMX on that generation of CR250's and tried every slide and nozzle known to man. Keihin = less headache and way more consistency, not to mention the increase of torque (about .5 lb-ft) up the whole front side.

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12/11/2018 6:52 AM
Edited Date/Time: 12/11/2018 6:50 PM

DynoDan22 wrote:

Honda H&H: I will ask for the settings he went with.

H4L: The mikuni 38 TMX made little more at peak (like .2hp) more than the PWK AS 38mm but was down on torque from ~4k-9k rpm. The Keihin makes way more torque (both 36 and 38mm) than the Mikuni and carburates more cleanly. The '02-'07's just seems to really like the 36mm AS's. I battled for years with the TMX on that generation of CR250's and tried every slide and nozzle known to man. Keihin = less headache and way more consistency, not to mention the increase of torque (about .5 lb-ft) up the whole front side.

Interesting.. Thnxz for the info. Around 05-06 I tested with a 00 Keihin PWK 38mm on a 03 CR2 with PC mods & ended up with the Mikuni TMX 38mm due to how it feels mid- top. Recently picked up an 07 model I rode this past weekend that has Watts Perfections engine mods with a Keihin PWK 38mm. It feels like it gives some up top to the 03 & will be testing with the oem Mikuni my next ride.
Spoke to Chad Watts about both carbs last summer & he mentioned that when they were testing with RC's 02 CR2 HRC engine on the Dyno the Mikuni showed better gains mid-top vs. the Keihin PWK. They ended up going with the Mikuni TMX on the 02-03 CR's because of it.
He recommended the TMX with his engine package with jetting specs. He also does some mods to the TMX that help with performance.

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Speak softly and carry a big stick.