Jump to content

STIC block review 2006 CR250

Recommended Posts

Background:  For the last few years, the daily rider has been a 2005 CR250 with Pro Circuit cylinder and race fuel head (and an RB Designs pump gas head for practice) with PWK from a 99 KX250 with #7 slide,  powerjet circuit  blocked, and genuine Sumitomo connectors used to connect the TPS.  We tried various needles from Suzuki, Kawasaki and Yamaha and settled on the Yamaha N3EJ which is from the 2006 YZ250 with 45 pilot and 178 main, air screw at 1 1/2.  No other mods to the 05 engine were made.  The bike ran well.

The bike accumulated over 300 hrs on the meter and it came time to clean out the garage a little, so the 05 was sold with the stock Mikuni TMX and with the PC cylinder and head.

Took an all stock 2006 CR250 with 5 hours on it out of storage to replace the sold 05 as the new daily rider.  The stock engine with TMX (as we all know) is flat on the bottom, transitions into a very good mid range and signs off too early on top.  Part of the problem is the terrible stock head design with 0.084" stock squish clearance and wide squish band.  PC and RB corrected this with their previous work on the 05 engine with excellent results. Stock roll-on acceleration is another weak point.

STIC recently reduced the price on their STIC block, so one was ordered to be evaluated on a completely stock, nearly new engine.  The kit arrived with spare O-ring, spare Torx fasteners, T20 bit, and 48 pilot and 190 main already installed.  STIC suggested using the Mikuni 6BFY43-74 needle which is from a YZ125 with Yamaha part number 284-14116-J4-00 which we promptly ordered.  The YZ125 needle has a long straight section measuring 0.047" as the final diameter.  This is significantly thinner (richer) than the familiar N3EJ.  STIC recommends using 98 octane fuel, so this was accomplished using a 60/40 blend of 91 oct ethanol free pump gas and Sunoco Supreme leaded non-oxygenated race fuel with a resulting octane rating near 99.  Supreme is Sunoco's equivalent to VP C-12. Test elevation is 400 ft above sea level with temps in the 70's to 80's   

Initial ride:  Mid range and top end on the STIC equipped stock engine was nearly equal to the Pro Circuit 05 engine with pump gas setup. Very good improvement over stock in this area, however I was not satisfied with the off idle to mid range transition and reduced to a 45 pilot. This change brought somewhat of an improvement, so we went down to a 42 looking for better throttle response and roll-on.  With the 42 pilot, off idle began to feel hollow and was not a step in the right direction.  

Back to the shop to reinstall the familiar N3EJ and 45 pilot combo that worked well previously.  With the N3EJ installed, we saw somewhat better off idle and roll on, but top end over rev was reduced from the 6BFY43-74.  This indicated that the increased final daimeter on the N3EJ required an even larger main, so a 192 was installed which helped quite a bit.  However, off idle and roll on were still not satisfactory.  This is an extremely important RPM and throttle opening range (in my opinion) for an MX engine to have ultra crisp throttle response in. For example, its important when blipping from whoop top to whoop top at a beat up sand track, or rolling on when exiting a tight corner.  Flat track, or ice racing applications which require more wide open throttle operation would be less critical here.

Called Derek Harris for his opinion.  Even though he did not sell us the STIC block, he was more than happy to help out (which says a lot about him).  Derek advised that a KTM customer was also having an issue in the low to mid transition range and they had good success with a minor mod to the STIC nozzle hood to effectively emulate the stock Keihin nozzle air bleed cutout.  The KTM engine is also a case-reed induction design, so there is some design commonality with the case reed Honda.  Derek suggested that we measure the stock Keihin hood cutout and start our mod with 75% of the stock dimension.  This was easily accomplished with a dremel tool in 5 minutes with our cut 0.100" wide and 0.060" deep.  

Back to the track for testing with the N3EJ, 45 pilot, 192 main, #7 slide and air screw at 1 1/2.  Big, big difference!!  Throttle response and low to mid transition were much better after the hood mod.  Still not quite as good as the stock Keihin block, but a major step in the right direction.  

Back to the shop and another call to Derek resulted in a decision to bring the STIC nozzle block air bleed cutout to match the Keihin measurements.   5 more minutes with the dremel gave the final cutout size 0.115" wide and 0.075" deep.  Track testing yielded excellent results.

While the carb was on the workbench we just happened to notice that the powerjet spray bar on Kawasaki and Yamaha PWK variants was directly in line upstream from the nozzle hood while a Suzuki variant had the powerjet spray bar canted at an angle above the nozzle and slide cutaway area.  Since the powerjet circuit can not be used with the stock Honda ECU and was previously blocked off at the brass jet, the spray bar served only to slightly interfere with airflow in this application.  We removed the spray bar and resumed testing.

End result:  Excellent.  Bike runs substantially better in the mid to top.  Over rev is increased.  RPM's build quicker. With the minor hood mod, off idle to mid range transition is very good and crisp.  Nice gains with no notable trade offs other than the possible exception of STIC's recommendation of using higher octane fuel. 

General observations: The STIC block requires a lot of fuel on the high speed circuits.  A 190 main was supplied with the kit and we went even further to 192 with the N3EJ.  Do not be afraid to start with a rich main jet. 

The idle circuit is changed.  We noted more idle screw inward adjustment is required to achieve the same idle as with the stock block. And, this is using a Kawasaki #7 slide which features a notch in the slide in front of the needle. The notch provides an an extra idle air bleed which reduces the amount of required slide opening height at idle    

The air screw is more sensitive to adjustment than with the stock block.  Some circuitry changes here, too.

Return on your investment/ value for the dollar:  Nobody likes to spend hard earned money on a product that does not provide satisfactory results.  IMO, the STIC block provides a very good value with solid performance gains for the money spent.

http://www.sticsupertorque.com/index.html

http://www.hpracedevelopment.com/

 

Edited by APBT
  • Like 7

Share this post


Link to post
Share on other sites

Here's a look at the stock Keihin nozzle air bleed cutout. 0.115" X 0.075".  Do exactly the same on your STIC block when its being used on a case reed Honda or KTM.  Future STIC variants will reportedly have this change. Credit Derek Harris.  http://www.Hpracedevelopment.com 

IMG_2079.JPG

Edited by APBT

Share this post


Link to post
Share on other sites

APBT - Thanks for posting.  It would have been good to have seen Dyno comparisons with the PC mods vs. the Stic mod on the Keihin carb.   When talking to the main guy in the engine dept. back in 2005 he stated that with the PC cyl / head mods you can expect a 10-15 % HP increase.  That was with optimal jetting & VP C12 & of course a fresh engine.   The metering Stick website link you posted above is claiming a 10% HP increase which is impressive for a bolt on part.  

A couple of questions :

1.  What expansion chamber are you running ? Stock or aftermarket ?

2.  What gear ratio combo ?

3. It appears to be a stock engine with no modifications ?  No correction of the squishband on the head ?      

Share this post


Link to post
Share on other sites

H4L,

This testing is with a 100% stock 2006 CR250 with 5 hours total time.  Stock expansion chamber, stock silencer, stock porting, stock head, stock ignition with Kawasaki PWK.  I used 13/48 gearing on the PC engine since it was strong enough to pull this combo.  Less shifting and a little more top speed. Continued this gearing onto this bike.  I plan on doing more engine work in the future.  The head mod alone yielded very good gains previously.  The stock setup is just a starting point to evaluate this product.  I like to make only one change at a time, then test again.  Just my personal preference.

The STIC setup would work well with your Pro Circuit engine.  A 10% gain with the STIC ??   I'm not sure, but it does build RPM's quicker and improve mid, top and over rev without any notable downside other than their recommendation to use 98 octane fuel.  It works well  

I think Derek posted a dyno of a YZ250 a while ago with the STIC on his website showing some nice gains of several hp.

Edited by APBT
  • Like 1

Share this post


Link to post
Share on other sites

Kawasaki places their powerjet spray bar directly in line with the top of the jet nozzle hood. Since the stock Honda ECU can not operate the powerjet solenoid, the circuit needs to be blocked off rendering it inoperative. We removed the spray bar to reduce turbulence and minor airflow obstruction. 

IMG_2080.JPG

Share this post


Link to post
Share on other sites
2 hours ago, APBT said:

The STIC setup would work well with your Pro Circuit engine.  A 10% gain with the STIC ??   I'm not sure about that, but it does build RPM's quicker and improve mid, top and over rev without any notable downside other than their recommendation to use 98 octane fuel.

 

Thanks for the feedback.  At my vet int. mx level I'm more then content with just the PC cyl / head mods.  I'm not even utilizing the full potential of the engine as is.

I understand about making changes one at a time so you can better evaluate the performance change if any.  I figured the 10% HP claim was a bit misleading & more of marketing ploy.    

Edited by H4L

Share this post


Link to post
Share on other sites
4 hours ago, H4L said:

At my vet int. mx level I'm more then content with just the PC cyl / head mods.  I'm not even utilizing the full potential of the engine as is.

Nobody can fault you for just staying with the PC setup. It's a good running engine at a fair price. 

As for my own current riding speed, let's just say I'm at the creaky knees, sore back, stiff neck, clicky elbows level where getting out of bed in the morning can be a 15 minute ordeal ?

Edited by APBT
  • Like 1

Share this post


Link to post
Share on other sites

On Derek's website it says he has two variations of the stic. Do you know what he means by that? Pump vs race gas perhaps?

Share this post


Link to post
Share on other sites

APBT, nice write up.

It was incredibly observant of him on the powerjet bar location/angle.  I have worked on quite a few of these, mostly yamaha and kx, but a few RM's, and never noticed the RM had the bar angled.....

 

On our stage 2 carb mod, I'm removing the bar AND the air striker veins along with boring and tapers.  Coupled with the STIC, this is great for power gains in WOT applications.  But for 85 percent of the people out there - leaving the veins is a good thing - removing the PJ bar if not being used is also a good thing.

The mikuni needle employs a stepped tip.  I have been hand filing the keihin needle tips in our set ups to increase flow area at WOT. This has a few effects - and I suggest it for all users who are around 188 and up main size.

From an all stock mikuni to the STIC - peak hp of around 10 percent is reasonable on the honda if you dont live in freezing temperatures. I can try to secure a newer style engine to test this on - but on the 02 and 03 models, we see about that result.  Now - vs a very well jetted mikuni - no way.  But the daily variance and head ache of getting the mikuni this good is a pain- as most people know the keihin is great as is - and the STIC is icing on that cake IMHO.  

The squish mod to a cr is good as all know - but not as much in peak HP as people think.  On the 05-07 I suggest .045", and 50 ish percent band with +2 degree angle (about 10 deg cut) and small blending radius - and keeping compression in check around 13.2:1 uncorrected...which runs on pump usually.  I've found that head mods require timing mods - for reasons not worth going to heavily into - but you may be surprised to need more advance on a tighter squish.

 

Lastly - I've found the cr's and KTM's to run on pump gs with the STIC - so if you wish to wean down to less and less race fuel APBT - you can.

 

 

This year continues to be swamped for me...finally seeing light at the end of the tunnel on getting some work out of the way...and with that will come more objective tests - with more data in various forms.  

  • Like 2

Share this post


Link to post
Share on other sites
44 minutes ago, harrperf said:

APBT, nice write up.

It was incredibly observant of him on the powerjet bar location/angle.  I have worked on quite a few of these, mostly yamaha and kx, but a few RM's, and never noticed the RM had the bar angled.....

 

On our stage 2 carb mod, I'm removing the bar AND the air striker veins along with boring and tapers.  Coupled with the STIC, this is great for power gains in WOT applications.  But for 85 percent of the people out there - leaving the veins is a good thing - removing the PJ bar if not being used is also a good thing.

The mikuni needle employs a stepped tip.  I have been hand filing the keihin needle tips in our set ups to increase flow area at WOT. This has a few effects - and I suggest it for all users who are around 188 and up main size.

From an all stock mikuni to the STIC - peak hp of around 10 percent is reasonable on the honda if you dont live in freezing temperatures. I can try to secure a newer style engine to test this on - but on the 02 and 03 models, we see about that result.  Now - vs a very well jetted mikuni - no way.  But the daily variance and head ache of getting the mikuni this good is a pain- as most people know the keihin is great as is - and the STIC is icing on that cake IMHO.  

The squish mod to a cr is good as all know - but not as much in peak HP as people think.  On the 05-07 I suggest .045", and 50 ish percent band with +2 degree angle (about 10 deg cut) and small blending radius - and keeping compression in check around 13.2:1 uncorrected...which runs on pump usually.  I've found that head mods require timing mods - for reasons not worth going to heavily into - but you may be surprised to need more advance on a tighter squish.

 

Lastly - I've found the cr's and KTM's to run on pump gs with the STIC - so if you wish to wean down to less and less race fuel APBT - you can.

 

 

This year continues to be swamped for me...finally seeing light at the end of the tunnel on getting some work out of the way...and with that will come more objective tests - with more data in various forms.  

Is the air bleed mod something you are recommending to people running these on the older screw top carbs like I have on my 03 250?  I'm not necessarily having issue with throttle response but I could always use a little more bottom end response.  Any downsides to this mod you can think of?

Share this post


Link to post
Share on other sites
3 hours ago, APBT said:

Nobody can fault you for just staying with the PC setup. It's a good running engine at a fair price. 

As for my own current riding speed, let's just say I'm at the creaky knees, sore back, stiff neck, clicky elbows level where getting out of bed in the morning can be a 15 minute ordeal ?

I'm not a young gun like I use to be so I can relate.

Yeah for the $300 I paid on PC mods the engine runs stronger from Bottom to top / overrev than (5) 450's owned..    Couldn't ask for a better engine package in my case.

Share this post


Link to post
Share on other sites
23 hours ago, APBT said:

  STIC suggested using the Mikuni 6BFY43-74 needle which is from a YZ125 with Yamaha part number 284-14116-J4-00 which we promptly ordered.  The YZ125 needle has a long straight section measuring 0.047" as the final diameter.  This is significantly thinner (richer) than the familiar N3EJ.  STIC recommends using 98 octane fuel, so this was accomplished using a 60/40 blend of 91 oct ethanol free pump gas and Sunoco Supreme leaded non-oxygenated race fuel with a resulting octane rating near 99.  Supreme is Sunoco's equivalent to VP C-12. Test elevation is 400 ft above sea level with temps in the 70's to 80's   

 

Am I understanding this correctly, you ran the Mikuni needle in the Keihin carb? Thought the Mikuni clip was too big to fit into the recess in the Keihin slide?

Edited by hallsy

Share this post


Link to post
Share on other sites

Hallsy,

Here's the Mikuni 6BFY43-74, Yamaha part no 284-14116-J4-00 with Mikuni clip attached, Yamaha part no 3MA-14159-00-00

Note the final diameter profile of this needle at WOT  

IMG_2089.JPG

Edited by APBT

Share this post


Link to post
Share on other sites

Here's the Mikuni needle outside diameter at the clip grooves. 

IMG_2090.JPG

Share this post


Link to post
Share on other sites

Here's the Keihin N3EJ, Yamaha part no 4SR-14916-EJ-00 with Keihin clip attached, Yamaha part 4MX-14919-00-00

IMG_2091.JPG

Share this post


Link to post
Share on other sites

Here's the Keihin N3EJ outside diameter at the grooves. 

IMG_2092.JPG

Share this post


Link to post
Share on other sites

The 6BFY43-74 fully seated in a sample Kawasaki PWK slide. There is enough clearance on the clip outside diameter and needle groove OD to fit into the PWK slide  even though the Mikuni setup is a few thousandths larger. If you're not comfortable with the amount of clearance at the clip grooves, you could always enlarge the hole diameter by a thousandth or two.  The clip has plenty of space  

Note that Kawasaki machines in an idle bleed air notch in front of the needle at the slide base which allows for idle with less slide opening. 

RB will machine your slide to this spec for only a few dollars. I'm sure Derek can also do the same. 

IMG_2093.JPG

Edited by APBT

Share this post


Link to post
Share on other sites
On 7/5/2017 at 5:07 PM, c-slak said:

Is the air bleed mod something you are recommending to people running these on the older screw top carbs like I have on my 03 250?  I'm not necessarily having issue with throttle response but I could always use a little more bottom end response.  Any downsides to this mod you can think of?

I leans the very early portion of throttle opening to about 3/8

If this is a problem area for you it may be worth it - I suggest stepping into it like APBT did - half notch at first.
 

If you spent large time on the straight diameter section of needle and all your settings - it's feasible it wont help much.  I've found it to be very subjective to the user...which is true of all riding in general.  Some love it, some cant' tell any difference, some may not "love it". But on the case reed hondas and ktm - especially in good working order with tightly sealed cases and good ring seal - where carb signal is good - Yes I like the notch.

Share this post


Link to post
Share on other sites
10 hours ago, APBT said:

Hallsy,

Here's the Mikuni 6BFY43-74, Yamaha part no 284-14116-J4-00 with Mikuni clip attached, Yamaha part no 3MA-14159-00-00

Note the final diameter profile of this needle at WOT  

IMG_2089.JPG

Thanks for the pics! I think I understand now what's going on. I have the 01'-03" CR 250 TMX which as your probably aware of is a different design (matchbox slide vs. crescent slide) than the 04'-07' CR 250 TMX. The O.D. of the 01'-03' needle clip that I have measures .257" and will not fit in the recess of the PWK slide. Thinking Mikuni used different clips in the different TMX. Could not prove via a Honda fiche as Honda didn't offer the clip as a separate part from the needle. However Yamaha does, the clip for the matchbox TMX = part# 25G-14919-00-00 vs. the clip for the crescent TMX = 3MA-14159-00-00. 

In regards to the final diameter profile of the needle, in your pic it appears that it reduces rather quickly to a final diameter that is straight as opposed to tapered. Is that correct?   

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:


×