RK Tek Head Installed. Ask and Truth shall be revealed

[xtactical]

Yep I broke down and finally went RK not becuase of the crummy sales tactics of some members but becuase I wanted to honestly review the head and craftsmanship for myself. 

Ordering Process 

I sent a few general emails wanting to know some simply questions like how does the squish come set on the head and what kind of compression should I expect?  Both questions were avoided and info was never provided, even after 3 separate emails asking for any info at all. No one would provide any information, so I went ahead and orderd a version I thought would be best since RK Tek was not providing any info, help or feedback. 

Order Followup

After ordering called Kelsey two days later to ask the same questions I had emailed about (compression, jetting so on). This time Kelsey was a little bit more helpful although not answering my questions directly I finally pulled a few recommendations from him. Seems like a standup guy though who knows his 2 strokes.

The Setup 

KTM 09 300 SX. installed th RK Tek. looks and bling factor A++ beautifully machined piece of work although the Orange heads look more like gold. Zero install issues.

The Performace 

Started bike on he stand. Immediately noticed the bike was a good bit louder with more throaty sound. Warmed up it revs fast and smooth and rpm falls as it should with no pipe bang. I noticed I significant overrev which was not present with my sx head.

Trail Performace 

Immediately I notice it is a lot louder and it has a richer sound to it. I noticed it would load up more than last head if i let rpms stay low for too long, consequently it was lacking right off the bottom, I may be able to jet this out of the bottom, however the bottom was definitely its weak point. Not only did the head not add anything to the bottom it may have even taken a bit away, granted that’s with the jetting being to rich on pilot. FYI These jetting specs ran perfect on my shaved SX head.

Real  Performance 

So getting on it once warmed up was not what I was expecting... Once I got past the sluggish bottom BOOM out of no where the mid range takes off like rocket. The Mids pull so hard it feels like when I run the red spring and set it to open early. It just comes on so quick and suddenly it’s actually difficult to keep the front down. It has a much more “2 stroke” feel to it. 

The high rpm range is maybe slighy better but not impressive like the mid range hit, good news is the over rev is very noticeable and can go further without a shift. 

I have a feeling if I put the red spring back in with this setup the bike would be so easy to loop it would just do it at the flick of your wrist

Final Thoughts

Im trying to figure out how to increase lows (lean pilot) tame the mids with more fuel and PV adjustments and keep a liner power through the rev range and i’ll be extremely happy if i can do those things. These heads are a gorgeous piece of machined bling, better cooling, and strong increase in power and for this i’m very happy with mine 8/10 score 

 

 

 

 

 

 

 

Edited May 20, 2018 by xtactical

[mog]

I suspect once you get the pilot right the transition won't be so bad

[redrider144]

Did you take any measurements for comparison?

Squish clearance: SX vs RK

Compression:  SX vs RK

[Tahoe Gator]

YZ250X owner with RK Tek, so take this with a grain of salt for KTMs, but over on the Yamaha 2-stroke forum there is a jetting post by Klinger 317 that I followed that seems to match the RK Tek head well. I don’t have the bottom lag you do. Then again, I was going from an OEM head (not a cut head).

FWIW, I did measure my squish pre and post: 0.105” to 0.047”

[mog]

The rk head uses much tighter squish with much more volume in the head ,it's funny as the 01 KTM 125 I had used this same idea ,it was almost a top hat shape as it has so much volume in the "dome"

 

The trbke is without afr readings you don't know if the extra rev is purely down to a slightly lean setting on the main , the bottom hit sounds like jetting would cure it , trial and error time ,just like us all lol

 

 

[xtactical]

8 hours ago, redrider144 said:

Did you take any measurements for comparison?

Squish clearance: SX vs RK

Compression:  SX vs RK

Yes, my original squish on SX was 1.90mm with 210psi RK is right about .90. with 205 psi

[redrider144]

1 hour ago, xtactical said:

Yes, my original squish on SX was 1.90mm with 210psi RK is right about .90. with 205 psi

Thanks.  The head you pulled off though, your cut SX head, was the comparison I'm after.  I think you had that one at:

• squish clearance:  1.1 mm
• compression:  210 psi

Now with RK you're at 0.9mm / 205 psi.

Edit:  Did you take any comparison photos to note the difference in the squish area between the two heads?

Edited May 20, 2018 by redrider144

[GHILL28]

What are your jetting/carb/elevation/fuel specs?

[xtactical]

2 hours ago, redrider144 said:

Thanks.  The head you pulled off though, your cut SX head, was the comparison I'm after.  I think you had that one at:

• squish clearance:  1.1 mm
• compression:  210 psi

Now with RK you're at 0.9mm / 205 psi.

Edit:  Did you take any comparison photos to note the difference in the squish area between the two heads?

After cutting the SX down I was right around 1.1mm and 210psi, I did have to open the bowl volume to achieve the 210psi once squish was corrected. Don’t have pics of both (just yet) but squish band does appear a bit more narrow on the RK

[xtactical]

1 hour ago, GHILL28 said:

What are your jetting/carb/elevation/fuel specs?

My SX jetting and first test for RK was Keihin 36mm - 38p NEDH 4th clip, 168 main. Sea level,  93 pump 60:1 mix

Just dropped the PJ to 35 since i was loading up with RK and sounds much better now. Oh, I also dropped in my N2ZW which is slightly leaner than the NEDH

Edited May 20, 2018 by xtactical

[GHILL28]

WAY too lean.

[xtactical]

3 minutes ago, GHILL28 said:

WAY too lean.

Just curious but why would you think so? It’s actually pretty rich. Moreso than KTM recommended jetting

[GHILL28]

45 175

[redrider144]

9 minutes ago, GHILL28 said:

WAY too lean.

He's running a NEDH in the 4th clip position.  The H diameter is fairly rich, makes sense that he'd be running a relatively small pilot.  As for the main, I'd say 168 is right on for the NEDH needle.  

Also note the D is equivalent to a NECH at 4.5.  He's getting on the taper sooner in the throttle range compared to a NECH in clip 3.  Again, not surprised that he's running a relatively small pilot.

He's also at 60:1 fuel:gas mix which also richens the fuel mixture slightly vs say 40:1.

Just now, GHILL28 said:

45 175

What needle / clip position?

Edited May 21, 2018 by redrider144

[GHILL28]

NEDG or H 3rd clip 7 slide

[mog]

After cutting the SX down I was right around 1.1mm and 210psi, I did have to open the bowl volume to achieve the 210psi once squish was corrected. Don’t have pics of both (just yet) but squish band does appear a bit more narrow on the RK

That's why it's got better overrev ,the narrow squish band width compared to yours, tends to trade bottom for top

[xtactical]

7 minutes ago, GHILL28 said:

45 175

I tested both 170 and 175 mains at colder temps (60F) the 175 would bog and wanted to die at WOT the 170 was ok but still would gargle from time to time which is why I found the 168 to be just right for me 

[GHILL28]

I just re-read it.  I'm running a 38mm carb with mine, and also running CA 91 gas too.  Nonetheless, the baseline he gave me for 2500-6k feet with those two factors was 42/175.  I'd expect one step richer from there for running at sea level.  Most jetting specs stay the same between a 36mm carb and 38mm carb however.

[mog]

How did this turn out ?

[mxaniac]

On 5/19/2018 at 8:17 PM, xtactical said:

So getting on it once warmed up was not what I was expecting... Once I got past the sluggish bottom BOOM out of no where the mid range takes off like rocket. The Mids pull so hard it feels like when I run the red spring and set it to open early. It just comes on so quick and suddenly it’s actually difficult to keep the front down. It has a much more “2 stroke” feel to it. 

From the dyno charts I saw posted the heavier springs and high preload (turning the adjuster clockwise) doesn't shift the powerband as much as it just clips it which seems ridiculous.  A flywheel weight seems like a much better way to tame a heavy hit than neutering it.  Regardless thanks for the ride report I've been thinking about getting this mod done on my 250.