2007 CR250 keihin carb swap

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7/4/2018 6:23 AM

Hi guys, just looking at swapping out my Mikuni for a keihin airstryker. I was wondering what my best option is? Getting one directly through jd jetting or am I better off sourcing a second hand one from another bike and if so what model works the best with 2007 CR250 and should I be looking at one with tps?

Thanks

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7/4/2018 7:25 AM

If it was me, I would go new and thru JD. Get the short body. As far as the TPS, you won't miss it.

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vomiting equals disqualification.

7/4/2018 7:32 AM

A lot of guys use a short body PWK from a late model YZ250, KX or RM. Al of these carbs have a throttle position sensor and powerjet circuit.
Your stock Honda ECU will not be able to operated the PWK powerjet circuit since the stock Mikuni was not equipped with one. Since the PWK powerjet is energized closed and de-energized open, the circuit will be continuously open and flowing fuel at all times which will mess up your jetting unless you block the circuit off. A lot of guys will solder or epoxy the brass powerjet jet closed and re-install the jet, or just remove the jet and install a set screw. Either technique accomplishes the same thing.
There is a guy on TT who sells pre-fabricated Throttle Postion Sensor kits using genuine Sumitomo connectors to perfectly fit the connectors you have on your Honda. Just tell him which carb you are using (The YZ, KX or RM version) and he sends you the correct connector kit. Search Honda 2 stroke forum over there.
Many guys report good results from installing a STIC metering block in the PWK.

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7/4/2018 7:35 AM

BR8ES wrote:

If it was me, I would go new and thru JD. Get the short body. As far as the TPS, you won't miss it.

If the TPS is not connected, the ignition will default to 2D map instead of 3D.
Not a huge difference, but a sensitive test rider can tell.

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7/4/2018 8:21 AM

BR8ES wrote:

If it was me, I would go new and thru JD. Get the short body. As far as the TPS, you won't miss it.

40 wrote:

If the TPS is not connected, the ignition will default to 2D map instead of 3D.
Not a huge difference, but a sensitive test ...more

Thanks for the advice guys, I’ll keep an eye out see if any decent ones come available on eBay or on here. Checked before and couldn’t find anything.

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7/4/2018 2:14 PM
Edited Date/Time: 7/4/2018 2:22 PM

Dobson110 wrote:

Thanks for the advice guys, I’ll keep an eye out see if any decent ones come available on eBay or on here. Checked before and ...more

Here's one from an RM. There are a few KX carbs on there, too. Many of them came stock with a #7 slide, but there were differences. A handy quick reference is the Pro Circuit Jetting Specs table.

https://www.ebay.com/itm/2003-SUZUKI-RM250-CARBURETOR-ASSEMBLY/253725710097?fits=Model%3ARM250&hash=item3b133b1711:g:BvkAAOSwFb5aJHKC

https://www.procircuit.com/jetting-specs.htm

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7/4/2018 5:45 PM

40 wrote:

Here's one from an RM. There are a few KX carbs on there, too. Many of them came stock with a #7 slide, but there were ...more

Thanks for finding that. I’ve just messaged the guy to see if he would post to Australia. In your experience what would you suggest as a good base jetting spec?

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7/5/2018 8:23 AM

Dobson110 wrote:

Thanks for finding that. I’ve just messaged the guy to see if he would post to Australia. In your experience what would you ...more

N3EJ (yamaha needle) 3rd clip, 45 pilot, 175 main, #7 slide, 2 turns out on the airscrew.
A lot of guys use the triple taper Suzuki needles with good results. A few guys use the Yamaha N8RJ or N3EW which are 1 and 2 steps richer than the N3EJ respectively. Again, lots of good info on TT..
Also, watch the slides when you're buying a PWK. Believe the 03 RM250 used a #6.5 which is 1/2 step richer than #7. Buying replacement slides is expensive, however you can always have a richer slide machined to a leaner number, but not the other way around.
A few reports indicate the cheap eBay Chinese knock off long body PWK's without TPS work pretty well also. Something like $50 new.

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7/5/2018 8:36 AM

Also, if you have'nt already done so- the stock engine needs work. The stock porting is not terrible, but the head squish and design is enormous which resluts in jetting instability and detonation.
Pro Circuit actually has a good cylinder and head package for under $400. I think Vital member "H4L" has experience with that setup. Maybe PM him for his input.
However, there are a lot of other good tuners like Tom Morgan, Terry Varner, Chad Watts etc who can help you.
The ignition can be advanced 2 to 3 degrees without losing top end and improving low-mid. A worthwhile mod that costs nothing. The stock pipe is pretty good also.

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7/5/2018 7:22 PM

Really the only PWK that will fit correctly on the 2004-2007 CR250 is the OEM ones from the YZ/RM/KX. None of the aftermarket ones from JD/SUDCO/etc are as short front to rear. Another member on here put a JD PWK on his 2004 and it was just too long and fit horribly. It wouldn't sit straight in the reed block boot and held the air boot cockeyed near the shock. These longer ones fit well on the 2002-2003 CR250. Perhaps using the older airboot on the 2004-2007 would make them fit? I don't know. Do some searching on here. There are a bunch of threads from user CamP where he dialed in a 2007 with a YZ250 PWK. He passed on tons of first hand knowledge.

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Powerband in every gear !

7/6/2018 5:18 AM

FGR01 wrote:

Really the only PWK that will fit correctly on the 2004-2007 CR250 is the OEM ones from the YZ/RM/KX. None of the aftermarket ...more

Believe you'll need to use a shorter airboot if you try using the long body PWK on the 04-07

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7/6/2018 7:57 AM

40 wrote:

N3EJ (yamaha needle) 3rd clip, 45 pilot, 175 main, #7 slide, 2 turns out on the airscrew.
A lot of guys use the triple taper ...more

The long body PWK's will work on the 04'-07' CR's but the fitment is not ideal. Like 40 mentioned above, if you do go with a used OEM short body PWK the power jet will need to be plugged. I used solder to plug the small jet power jet, and then just screwed it back it, but I believe a 2.5mm hex screw will do the same. If you do go with a Kawasaki oem carb, all of their short body 38mm carbs come with a #8 slide, which will require slightly different jetting than the #7 equipped PWK's. I have tons of jetting specs for either the #7 or #8 slide, depending on what type of riding you are doing. Also, if you go with a later model RM carb, they are actually 39mm, and will run ever so slightly different than the Yamaha and Kawasaki 38mm carbs. Here is a link to convert the Honda TPS to any of the other OEM carbs.

https://thumpertalk.com/forums/topic/1013742-keihin-pwk-airstriker-yz250-to-cr250-%E2%80%9Cstarter-kit%E2%80%9D-w-harness/?page=5#comment-11901947

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7/6/2018 8:41 AM

Dobson110 wrote:

Thanks for finding that. I’ve just messaged the guy to see if he would post to Australia. In your experience what would you ...more

40 wrote:

N3EJ (yamaha needle) 3rd clip, 45 pilot, 175 main, #7 slide, 2 turns out on the airscrew.
A lot of guys use the triple taper ...more

digger wrote:

The long body PWK's will work on the 04'-07' CR's but the fitment is not ideal. Like 40 mentioned above, if you do go with a ...more

Thanks for the advice guys, it’s all appreciated. I’m trying to find one with tps that will post to Australia, if I can’t find one I’ll get a short body from jd.

I plan to race mx once the bike is completed, in the early stages of the build at the moment, still cleaning everything up and trying to chase up all the parts now.

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7/18/2018 5:09 AM

I’ve got an 01 yz250 carby on its way. What do you guys think is a good base setting for my 07? The bike has a scalvini exhaust and pro circuit ti2 muffler, I’m running vforce reeds. The head will be done and the cylinder will be ported. I also have 6 x 1 inch uni filter vents (3 on each side) in the airbox to allow for more air.

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