Full Tilt CR250 Build - MXA Two Stroke Hall of Fame

Nickel44
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Nickel44 2/8/2017 10:32am
2/8/2017 10:32am
Sorry for the stupid translation, I am not good in your language, blackdiamond very nice Furum and top bike I like to read here. big respect. Here in Germany it is very difficult to keep a model running. If I want to have the ignition of 03 is enough when I change the CDI?
blackdiamond
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blackdiamond 2/8/2017 7:07pm
2/8/2017 7:07pm
What year bike is it?
pgd
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pgd 2/9/2017 4:40pm
2/9/2017 4:40pm
Hey blackdiamond, which brand exhaust pipe did you end up going with?
Nickel44
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Nickel44 2/9/2017 9:48pm
2/9/2017 9:48pm
blackdiamond wrote:
What year bike is it?
I have the model 2002

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blackdiamond
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blackdiamond 2/10/2017 9:21am
2/10/2017 9:21am
pgd wrote:
Hey blackdiamond, which brand exhaust pipe did you end up going with?
HGS
blackdiamond
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blackdiamond 2/10/2017 9:22am
2/10/2017 9:22am
Nickel44 wrote:
I have the model 2002
What carb are you trying to run?
Nickel44
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Nickel44 2/12/2017 11:35pm
2/12/2017 11:35pm
Nickel44 wrote:
I have the model 2002
blackdiamond wrote:
What carb are you trying to run?
I have a mikuni tmx 38 with a jd jettingkit
blackdiamond
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blackdiamond 2/13/2017 10:36am
2/13/2017 10:36am
Nickel44 wrote:
I have a mikuni tmx 38 with a jd jettingkit
Yea, the 2003 ignition will work fine but if you changed to the 2004-2007 box and wiring harness you could run a TPS carb if you wanted to.
Nickel44
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Nickel44 2/14/2017 1:23am
2/14/2017 1:23am
Would it be enough that I only exchange the cdi box from 02 to 03 or do I have to change the complete ignition?
blackdiamond
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blackdiamond 2/14/2017 8:58am
2/14/2017 8:58am
Nickel44 wrote:
Would it be enough that I only exchange the cdi box from 02 to 03 or do I have to change the complete ignition?
02 and 03 boxes are the same. 04-07 boxes are the same. You just have to use the same year wiring harness as the box, the rest of the electrical parts will work.
Nickel44
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Nickel44 2/14/2017 11:36pm
2/14/2017 11:36pm
I'm just wondering what was changed from Model 02 to 03 at the ignition like Timing and trying to figure out what
NEW FOR 2003:
New cylinder porting.
New eight-petal reed valve.
New air intake system offers straighter alignment to produce more direct airflow.
Redesigned number plate and inner duct.
New foam gasket between airbox and air boot for better sealing and airflow management.
New works-shaped expansion chamber.
New ignition timing settings help broaden the engine's powerband.

ENGINE:
Air intake boot is reshaped for more direct airflow, contributing to strong low-speed engine performance.
Five-speed close-ratio transmission features thicker second and third gears.
blackdiamond
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blackdiamond 2/15/2017 10:21am
2/15/2017 10:21am
Nickel44 wrote:
I'm just wondering what was changed from Model 02 to 03 at the ignition like Timing and trying to figure out what NEW FOR 2003: New...
I'm just wondering what was changed from Model 02 to 03 at the ignition like Timing and trying to figure out what
NEW FOR 2003:
New cylinder porting.
New eight-petal reed valve.
New air intake system offers straighter alignment to produce more direct airflow.
Redesigned number plate and inner duct.
New foam gasket between airbox and air boot for better sealing and airflow management.
New works-shaped expansion chamber.
New ignition timing settings help broaden the engine's powerband.

ENGINE:
Air intake boot is reshaped for more direct airflow, contributing to strong low-speed engine performance.
Five-speed close-ratio transmission features thicker second and third gears.
What exactly is your question?
H4L
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H4L 2/15/2017 8:03pm
2/15/2017 8:03pm Edited Date/Time 2/16/2017 7:31am
Nickel44 wrote:
I'm just wondering what was changed from Model 02 to 03 at the ignition like Timing and trying to figure out what NEW FOR 2003: New...
I'm just wondering what was changed from Model 02 to 03 at the ignition like Timing and trying to figure out what
NEW FOR 2003:
New cylinder porting.
New eight-petal reed valve.
New air intake system offers straighter alignment to produce more direct airflow.
Redesigned number plate and inner duct.
New foam gasket between airbox and air boot for better sealing and airflow management.
New works-shaped expansion chamber.
New ignition timing settings help broaden the engine's powerband.

ENGINE:
Air intake boot is reshaped for more direct airflow, contributing to strong low-speed engine performance.
Five-speed close-ratio transmission features thicker second and third gears.
The 03 cdi will have a better oem map to help broaden the powerband vs. the 02 oem cdi. If your running the 03 cyl porting specs I'd advise you to run the 03 oem cdi unlsess your planning to go aftermarket with the cdi. Then your able to customize a map to your engine specs as desired.
The ign. timing for 02 was 18 +/- 2 deg. @ 2000 RPM & the 03 is 20 +/- 1 deg. @ 4000 RPM per the service manual.
H4L
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H4L 2/17/2017 7:40am
2/17/2017 7:40am Edited Date/Time 2/17/2017 7:41am
BD - I'm planning on upgrading to an 06 CR250r bottom end & use a flat top piston with the 03 PC cyl. / head. The 05 + CR2's have the updated crank with out the tins around the journals is the main reason for wanting to do it. Also heard the CCV was reduced on the 05 + cases & not sure if that made much of a difference if any at all. Do you have info or insight on that or discussed that with Varner on the case differences between the 02-03 vs. 05-07 ? Thanks in advance...
blackdiamond
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blackdiamond 2/17/2017 10:03am
2/17/2017 10:03am
H4L wrote:
BD - I'm planning on upgrading to an 06 CR250r bottom end & use a flat top piston with the 03 PC cyl. / head. The...
BD - I'm planning on upgrading to an 06 CR250r bottom end & use a flat top piston with the 03 PC cyl. / head. The 05 + CR2's have the updated crank with out the tins around the journals is the main reason for wanting to do it. Also heard the CCV was reduced on the 05 + cases & not sure if that made much of a difference if any at all. Do you have info or insight on that or discussed that with Varner on the case differences between the 02-03 vs. 05-07 ? Thanks in advance...
I actually like the way the 03 runs best. Once the engines are modded and the compression and timing are bumped up the CCV doesn't seem to matter much on any of the 02-07 engines. The 03 just seems to have a bit more over-rev IMO.
H4L
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H4L 2/17/2017 10:40am
2/17/2017 10:40am
blackdiamond wrote:
I actually like the way the 03 runs best. Once the engines are modded and the compression and timing are bumped up the CCV doesn't seem...
I actually like the way the 03 runs best. Once the engines are modded and the compression and timing are bumped up the CCV doesn't seem to matter much on any of the 02-07 engines. The 03 just seems to have a bit more over-rev IMO.
Thought so on the cases. Thanks for confirming. Agree on the 03 cyl with having more topend / overev. The 05-07 engines feel like 02 & 04 YZ250's owned where they sign off on top in comparison to the 02-03 CR2's.
40
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40 2/19/2017 9:35am
2/19/2017 9:35am
H4L wrote:
Thought so on the cases. Thanks for confirming. Agree on the 03 cyl with having more topend / overev. The 05-07 engines feel like 02 &...
Thought so on the cases. Thanks for confirming. Agree on the 03 cyl with having more topend / overev. The 05-07 engines feel like 02 & 04 YZ250's owned where they sign off on top in comparison to the 02-03 CR2's.
Wonder if the STIC block on the PWK would help the top end over-rev issue on the '05-'07 engines? Most guys report a stronger top end when using the STIC.
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H4L 2/19/2017 11:28am
2/19/2017 11:28am Edited Date/Time 2/19/2017 11:29am
40 wrote:
Wonder if the STIC block on the PWK would help the top end over-rev issue on the '05-'07 engines? Most guys report a stronger top end...
Wonder if the STIC block on the PWK would help the top end over-rev issue on the '05-'07 engines? Most guys report a stronger top end when using the STIC.
I can't comment on how the stic block would affect the topend (don't own one), but a word of caution if your planning on buying one. A few of the first buyers reported detonation after initial use. It seems you have to run at least 4-5 mj sizes bigger & higher octane fuel.

A better way to go about getting more topend out of the 05-07's is cyl port work & head mods IMHO. I recently purchased an HGS pipe & JD ign. for an 06-07 owned. Besides having the squish tightened to about .040" & having
it reshaped for pump fuel. It should provide a very strong broad powerband with a healthy topend.

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blackdiamond
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blackdiamond 2/19/2017 12:13pm
2/19/2017 12:13pm
40 wrote:
Wonder if the STIC block on the PWK would help the top end over-rev issue on the '05-'07 engines? Most guys report a stronger top end...
Wonder if the STIC block on the PWK would help the top end over-rev issue on the '05-'07 engines? Most guys report a stronger top end when using the STIC.
H4L wrote:
I can't comment on how the stic block would affect the topend (don't own one), but a word of caution if your planning on buying one...
I can't comment on how the stic block would affect the topend (don't own one), but a word of caution if your planning on buying one. A few of the first buyers reported detonation after initial use. It seems you have to run at least 4-5 mj sizes bigger & higher octane fuel.

A better way to go about getting more topend out of the 05-07's is cyl port work & head mods IMHO. I recently purchased an HGS pipe & JD ign. for an 06-07 owned. Besides having the squish tightened to about .040" & having
it reshaped for pump fuel. It should provide a very strong broad powerband with a healthy topend.
I am going to be testing one on a new carb setup in the next few weeks so we'll see.
40
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40 2/19/2017 12:59pm
2/19/2017 12:59pm


Looks like Derek achieved some nice gains on a YZ250 with the STIC. Not sure about the fuel he was using, or how the STIC would work on a CR250, but this looks like a good gain.

40
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40 2/19/2017 1:04pm
2/19/2017 1:04pm


Here's another example from Derek's website of a KTM 300 with the STIC. The KTM's use a case reed engine design, so maybe this would be more approximate to what can be expected on a CR250??

H4L
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H4L 2/19/2017 1:22pm
2/19/2017 1:22pm
The 02-07 CR250r mikuni provides better topend power vs. the keihin PWK. Over on TT I did ask him if he was going to have a dyno comparison of a 03 CR2 with a well jetted mikuni vs. the Keihin with the stic block. He said he was going to try to do a dyno comparison since he was working on an 03 for a customer. This was back late last yr., but I haven't seen him post any dyno info on it.
For now I'm sticking with a well jetted mikuni on the 05-07 CR2 since I know they perform better in the topend. Boswell the inventor of the stic block is suppose to come out with a mod for the mikuni this spring possibly. I'm thinking of trying that out if the test ride results are positive.
40
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40 2/19/2017 2:00pm
2/19/2017 2:00pm
H4L wrote:
The 02-07 CR250r mikuni provides better topend power vs. the keihin PWK. Over on TT I did ask him if he was going to have a...
The 02-07 CR250r mikuni provides better topend power vs. the keihin PWK. Over on TT I did ask him if he was going to have a dyno comparison of a 03 CR2 with a well jetted mikuni vs. the Keihin with the stic block. He said he was going to try to do a dyno comparison since he was working on an 03 for a customer. This was back late last yr., but I haven't seen him post any dyno info on it.
For now I'm sticking with a well jetted mikuni on the 05-07 CR2 since I know they perform better in the topend. Boswell the inventor of the stic block is suppose to come out with a mod for the mikuni this spring possibly. I'm thinking of trying that out if the test ride results are positive.
Thinking the '04-'07 TMX with TPS was better sorted out than the earlier variants used on the '02-'03.
That will be an interesting comparison- a newer style TMX versus a PWK with STIC.
Maybe the newer style TMX with STIC will be a really good setup?
H4L
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H4L 2/19/2017 2:44pm
2/19/2017 2:44pm Edited Date/Time 2/19/2017 2:55pm
40 wrote:
Thinking the '04-'07 TMX with TPS was better sorted out than the earlier variants used on the '02-'03. That will be an interesting comparison- a newer...
Thinking the '04-'07 TMX with TPS was better sorted out than the earlier variants used on the '02-'03.
That will be an interesting comparison- a newer style TMX versus a PWK with STIC.
Maybe the newer style TMX with STIC will be a really good setup?
Agree. The 04-07 CR250r mikuni with tps seems to perform better at lower rpm throttle position openings vs. the older 02-03 longer body version. The TB on the 04-07 CR2 tmx version is shaped more like the TB on the Keihin pwk. The 02-03 TB is shaped like a match box & read somewhere that this is the main reason for how it doesn't perform as well at lower throttle positions.
Currently running an 00 Keihin pwk on an 03 CR2 with good results on the topend. I did notice a little loss off the top, but the trade off was worth the better throttle response. It already has an excellent topend / overev with the PC cyl & head mods..
blackdiamond
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blackdiamond 2/19/2017 5:01pm
2/19/2017 5:01pm
H4L wrote:
The 02-07 CR250r mikuni provides better topend power vs. the keihin PWK. Over on TT I did ask him if he was going to have a...
The 02-07 CR250r mikuni provides better topend power vs. the keihin PWK. Over on TT I did ask him if he was going to have a dyno comparison of a 03 CR2 with a well jetted mikuni vs. the Keihin with the stic block. He said he was going to try to do a dyno comparison since he was working on an 03 for a customer. This was back late last yr., but I haven't seen him post any dyno info on it.
For now I'm sticking with a well jetted mikuni on the 05-07 CR2 since I know they perform better in the topend. Boswell the inventor of the stic block is suppose to come out with a mod for the mikuni this spring possibly. I'm thinking of trying that out if the test ride results are positive.
A lot of people say that but I have never tested them back to back on the CR to confirm either way. I do know for a fact however that swapping a 38 Mikuni for a 38 Keihin gains almost 2 HP on the new KTM 250.

That bike reacts the exact opposite of what many people claim to be true.
blackdiamond
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blackdiamond 2/19/2017 5:29pm
2/19/2017 5:29pm Edited Date/Time 2/19/2017 5:30pm
40 wrote:
Thinking the '04-'07 TMX with TPS was better sorted out than the earlier variants used on the '02-'03. That will be an interesting comparison- a newer...
Thinking the '04-'07 TMX with TPS was better sorted out than the earlier variants used on the '02-'03.
That will be an interesting comparison- a newer style TMX versus a PWK with STIC.
Maybe the newer style TMX with STIC will be a really good setup?
H4L wrote:
Agree. The 04-07 CR250r mikuni with tps seems to perform better at lower rpm throttle position openings vs. the older 02-03 longer body version. The TB...
Agree. The 04-07 CR250r mikuni with tps seems to perform better at lower rpm throttle position openings vs. the older 02-03 longer body version. The TB on the 04-07 CR2 tmx version is shaped more like the TB on the Keihin pwk. The 02-03 TB is shaped like a match box & read somewhere that this is the main reason for how it doesn't perform as well at lower throttle positions.
Currently running an 00 Keihin pwk on an 03 CR2 with good results on the topend. I did notice a little loss off the top, but the trade off was worth the better throttle response. It already has an excellent topend / overev with the PC cyl & head mods..
Here is a screenshot of a 2017 KTM with the Keihin swap.

1.3 HP at peak and 7.4 HP at 9500 RPM

Both runs with 91 pump fuel and HGS pipe and silencer. The rest of the motor was stock.



blackdiamond
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blackdiamond 2/19/2017 5:32pm
2/19/2017 5:32pm
40 wrote:
Thinking the '04-'07 TMX with TPS was better sorted out than the earlier variants used on the '02-'03. That will be an interesting comparison- a newer...
Thinking the '04-'07 TMX with TPS was better sorted out than the earlier variants used on the '02-'03.
That will be an interesting comparison- a newer style TMX versus a PWK with STIC.
Maybe the newer style TMX with STIC will be a really good setup?
H4L wrote:
Agree. The 04-07 CR250r mikuni with tps seems to perform better at lower rpm throttle position openings vs. the older 02-03 longer body version. The TB...
Agree. The 04-07 CR250r mikuni with tps seems to perform better at lower rpm throttle position openings vs. the older 02-03 longer body version. The TB on the 04-07 CR2 tmx version is shaped more like the TB on the Keihin pwk. The 02-03 TB is shaped like a match box & read somewhere that this is the main reason for how it doesn't perform as well at lower throttle positions.
Currently running an 00 Keihin pwk on an 03 CR2 with good results on the topend. I did notice a little loss off the top, but the trade off was worth the better throttle response. It already has an excellent topend / overev with the PC cyl & head mods..
Sorry, upload didn't stick, see below.



seth505
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seth505 2/19/2017 5:33pm
2/19/2017 5:33pm
blackdiamond wrote:
Here is a screenshot of a 2017 KTM with the Keihin swap. 1.3 HP at peak and 7.4 HP at 9500 RPM Both runs with 91...
Here is a screenshot of a 2017 KTM with the Keihin swap.

1.3 HP at peak and 7.4 HP at 9500 RPM

Both runs with 91 pump fuel and HGS pipe and silencer. The rest of the motor was stock.



Interesting, thanks for sharing. Do you know, is that with jetting tweaks on both carbs or factory settings on the Mikuni?
blackdiamond
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blackdiamond 2/19/2017 5:56pm
2/19/2017 5:56pm
Both carbs were jetted but the Mikuni was close out of the box from what I am told.
H4L
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H4L 2/19/2017 7:01pm
2/19/2017 7:01pm
blackdiamond wrote:
A lot of people say that but I have never tested them back to back on the CR to confirm either way. I do know for...
A lot of people say that but I have never tested them back to back on the CR to confirm either way. I do know for a fact however that swapping a 38 Mikuni for a 38 Keihin gains almost 2 HP on the new KTM 250.

That bike reacts the exact opposite of what many people claim to be true.
BD - I'm going off of a butt dyno & doing my own testing a few yrs. back. I don't have any actual dyno data & was the reason I asked the TT member for a dyno graph comparison of the two carbs. Boswell chimed in & commented that the mikuni tmx is a better carb in the upper rpm range.
Also was told that Chad Watts RC's factory mechanic talked about RC testing the Keihin PWK on his 02 CR2 & liking it. After doing some testing with both carbs they seen on the dyno graph that the mikuni provided more power & went with it instead.
Not sure if that is fact or fiction, but based off of the butt dyno it feels accurate that the mikuni does breath better up top.
It would be good to see a dyno graph comparison on the 03 CR2 to get a definitive answer.

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