'17 '18 250SX JM Racing Performance build

Pirate421
Posts
1812
Joined
7/26/2015
Location
MA US
12/5/2018 6:19pm
Awesome build and story. Are you still glad you went with the 250sx at Loretta’s? Do you wish you had a 450? Doesn’t look like it held you back that’s a lot of hardware, good ride!
Keating
Posts
128
Joined
7/4/2018
Location
Spring, TX US
12/6/2018 12:13pm
Pirate421 wrote:
Awesome build and story. Are you still glad you went with the 250sx at Loretta’s? Do you wish you had a 450? Doesn’t look like it...
Awesome build and story. Are you still glad you went with the 250sx at Loretta’s? Do you wish you had a 450? Doesn’t look like it held you back that’s a lot of hardware, good ride!
I'm really enjoying the 250 2-Smoke!! Like I said at the beginning of this thread, I only got to ride and work on this bike for a couple weeks before Loretta's... I just came off my YZ125, so had this 250 pretty de-tuned and even with the de-tuned power, I was able to put in some good motos and great passes on 450s!! I have gotten some more testing and riding time on this bike now and am getting a handle on the power and think I'll be able to put in a much better showing at LL19!!

I'm pretty old school and I think if you know how to ride a 2 stroke properly (and set one up) that you really don't give much up to the 4 strokes. Most guys these days have put in quite a bit of time on thumpers and get used to the "Lazy" style of riding/racing that these thumpers allow everybody to get away with....

The 4 strokes have a slight rideability advantage, but the 2 strokes have the Fun Factor advantage!! You gotta ride a 2 stroke like a 2 stroke! A little clutch work and some throttle control and you've got yourself a real contender in the Moto world!!!
2
Keating
Posts
128
Joined
7/4/2018
Location
Spring, TX US
12/20/2018 9:05am
Changing the Gearing!



Didn't have time to do any testing with different gearing before I went to Loretta's. I did, of course, have time after my couple weeks of recovery!!

Not a cop out, but gearing is somewhat a matter of preference! One thing to consider, is your riding style. Do you like to run a taller gear and use some clutch out of the corner or do you want the bike to come more alive without really using much clutch?? What type of track are you riding/racing? Does it have tight corners or sweepers, short or long straights, SX type jumps or gradual ski type jumps, how about hills?? Maybe all of the above..... If so, which parts of the track can you make up time on, or are tricky for you to navigate???

All the mags and testers say to drop the rear 1 tooth to a 49 and call it good. Well that doesn't always work for everybody.... Those testers & fans of the 49 were running the stock 50 at Glen Helen for the 2 Stroke National!!! Something to think about..... My buddy, SuperDave, runs the stock 50 on his TC250 and loves it because he can pull 3rd gear starts!! He also had JM Racing turn the motor into a Fire Breathing Dragon so it pulls plenty long into the top end and doesn't sign off...!!

You gotta get out there and test, guys! Take lap times if possible. Pick one section of your local track that's tight or really rough and spend some extra time there and try some different combinations to give you an idea of what gearing might work at different tracks that you go to or may end up at someday... Get a few different sprockets and try them out and see what works! There are pretty cheap steel sprockets out there that you can get a not break the bank, I wouldn't buy several Rental Chainwheels to experiment with, but that's just me!


Cheap steel sprocket for testing....

I personally like the 14/49 for most tracks since I run a taller gear in most sections and Always have that "Old School" 1 finger on the clutch at all times...!! On tighter tracks I'll throw that 50 back on there that I keep with other assorted parts in a cardboard box in my van on race day!!

I hope I gave you some good ideas on how to improve your gearing and get your lap times down!! Good luck with your testing and take some notes of what you think and feel about each gearing ratio you try!
2
AJ565
Posts
2075
Joined
3/12/2012
Location
San Antonio, TX US
12/20/2018 8:01pm
I’ve been wanting to try a 48 rear. Especially at cycle ranch where it’s wide open 3rd and 4th most of the track.

The Shop

opyguy
Posts
567
Joined
8/22/2016
Location
Boston, MA US
12/21/2018 8:37am
i run a 49, basically run 3rd/4th the whole track. Really struggling w/starts, killed them w/my 350 but suck on the 250 2 stroke.
cdoggy81
Posts
1305
Joined
1/1/2018
Location
St. Petersburg, FL US
12/21/2018 10:48am Edited Date/Time 12/21/2018 10:50am
Opyguy-if starts are giving you a hard time try a 50t rear but with a 120 rear tire... :-) It may cost you a clutch or 2 until you get it right but when you do you will be hookin & bookin ?
Keating
Posts
128
Joined
7/4/2018
Location
Spring, TX US
12/21/2018 11:44am
opyguy wrote:
i run a 49, basically run 3rd/4th the whole track. Really struggling w/starts, killed them w/my 350 but suck on the 250 2 stroke.
For me, I need to be a little more aggressive with the clutch on 2 stroke starts. I'd start in 2nd gear, just a touch more revs, and practice being a hair more aggressive on letting the clutch out....
opyguy
Posts
567
Joined
8/22/2016
Location
Boston, MA US
12/21/2018 11:47am
my problem is I'm too aggressive, bike wants to loop out or doesn't track straight...Ill keep practicing
Keating
Posts
128
Joined
7/4/2018
Location
Spring, TX US
12/21/2018 11:50am
cdoggy81 wrote:
Opyguy-if starts are giving you a hard time try a 50t rear but with a 120 rear tire... :-) It may cost you a clutch or...
Opyguy-if starts are giving you a hard time try a 50t rear but with a 120 rear tire... :-) It may cost you a clutch or 2 until you get it right but when you do you will be hookin & bookin ?
Cdoggy's idea will give you more control and traction with the 50, but I don't like not being able to break my back end loose and let it slide around the corner and steer it with the back end.... One of the things you can do on a Smoker, when needed! A large rear tire makes that really hard to do!!
Keating
Posts
128
Joined
7/4/2018
Location
Spring, TX US
12/21/2018 12:01pm
opyguy wrote:
my problem is I'm too aggressive, bike wants to loop out or doesn't track straight...Ill keep practicing
Wow, even with the 49??
Keating
Posts
128
Joined
7/4/2018
Location
Spring, TX US
12/21/2018 1:03pm
AJ565 wrote:
I’ve been wanting to try a 48 rear. Especially at cycle ranch where it’s wide open 3rd and 4th most of the track.
I've thought about that too! Let me know if you try it!
Superdave19
Posts
1102
Joined
10/10/2012
Location
Spring, TX US
12/21/2018 1:41pm
I've tried a 48-49-50-51... After my mods were done, always went back to a 50t.

Sometimes I lay awake at night thinking of how my JM Racing TC250 sounds on the pipe- Ahhh LoL

I recently found a cherry 19' KX450.. I've got a couple motos on a few different 19' KX450's.. and at this point, still prefer to ride the TC. For me it's just easier to push, and ride aggressive.

I've got some recent Helmet Cam at Cycle Ranch somewhere on my TC.. I'll try and post on a new thread as not to hijack-
2
Keating
Posts
128
Joined
7/4/2018
Location
Spring, TX US
12/26/2018 1:46pm
I've tried a 48-49-50-51... After my mods were done, always went back to a 50t. Sometimes I lay awake at night thinking of how my JM...
I've tried a 48-49-50-51... After my mods were done, always went back to a 50t.

Sometimes I lay awake at night thinking of how my JM Racing TC250 sounds on the pipe- Ahhh LoL

I recently found a cherry 19' KX450.. I've got a couple motos on a few different 19' KX450's.. and at this point, still prefer to ride the TC. For me it's just easier to push, and ride aggressive.

I've got some recent Helmet Cam at Cycle Ranch somewhere on my TC.. I'll try and post on a new thread as not to hijack-
How would you say that the JM Racing mods changed/improved the power and powerband??

And, there's not much better than the sound of a finely tuned 2 stroke on the pipe....!!!!
Superdave19
Posts
1102
Joined
10/10/2012
Location
Spring, TX US
12/27/2018 1:51pm
Keating wrote:
How would you say that the JM Racing mods changed/improved the power and powerband?? And, there's not much better than the sound of a finely tuned...
How would you say that the JM Racing mods changed/improved the power and powerband??

And, there's not much better than the sound of a finely tuned 2 stroke on the pipe....!!!!
The entire power band is much more broad, and over-rev is much improved. I use to have a dead spot between 3rd and 4th.. it'd run outta steam up top in 3rd, and I'd have to shift to 4th, but it would fall off a bit.

Now I just leave it in third. If I DO need to hit 4th, it now has the stones to pull it.. gap is gone.

I can't emphasize what a difference these mods made.

Freakin' fantastic 250-
1
Keating
Posts
128
Joined
7/4/2018
Location
Spring, TX US
12/27/2018 2:42pm
Keating wrote:
How would you say that the JM Racing mods changed/improved the power and powerband?? And, there's not much better than the sound of a finely tuned...
How would you say that the JM Racing mods changed/improved the power and powerband??

And, there's not much better than the sound of a finely tuned 2 stroke on the pipe....!!!!
The entire power band is much more broad, and over-rev is much improved. I use to have a dead spot between 3rd and 4th.. it'd run...
The entire power band is much more broad, and over-rev is much improved. I use to have a dead spot between 3rd and 4th.. it'd run outta steam up top in 3rd, and I'd have to shift to 4th, but it would fall off a bit.

Now I just leave it in third. If I DO need to hit 4th, it now has the stones to pull it.. gap is gone.

I can't emphasize what a difference these mods made.

Freakin' fantastic 250-
That's Awesome Bro!!! You may be a Permanent 2 Smoker....
BR8ES
Posts
1914
Joined
6/3/2018
Location
Bennett, CO US
12/27/2018 6:42pm
great thread, appreciate the background and fun times.
2
PJSMAN
Posts
17
Joined
1/15/2014
Location
Martinsville, IN US
7/31/2019 9:58am
Pirate421 wrote:
Awesome build and story. Are you still glad you went with the 250sx at Loretta’s? Do you wish you had a 450? Doesn’t look like it...
Awesome build and story. Are you still glad you went with the 250sx at Loretta’s? Do you wish you had a 450? Doesn’t look like it held you back that’s a lot of hardware, good ride!
Keating wrote:
I'm really enjoying the 250 2-Smoke!! Like I said at the beginning of this thread, I only got to ride and work on this bike for...
I'm really enjoying the 250 2-Smoke!! Like I said at the beginning of this thread, I only got to ride and work on this bike for a couple weeks before Loretta's... I just came off my YZ125, so had this 250 pretty de-tuned and even with the de-tuned power, I was able to put in some good motos and great passes on 450s!! I have gotten some more testing and riding time on this bike now and am getting a handle on the power and think I'll be able to put in a much better showing at LL19!!

I'm pretty old school and I think if you know how to ride a 2 stroke properly (and set one up) that you really don't give much up to the 4 strokes. Most guys these days have put in quite a bit of time on thumpers and get used to the "Lazy" style of riding/racing that these thumpers allow everybody to get away with....

The 4 strokes have a slight rideability advantage, but the 2 strokes have the Fun Factor advantage!! You gotta ride a 2 stroke like a 2 stroke! A little clutch work and some throttle control and you've got yourself a real contender in the Moto world!!!
How does the 250 2 stroke compare to the 350 4 stroke?
PJSMAN
Posts
17
Joined
1/15/2014
Location
Martinsville, IN US
7/31/2019 10:01am
Keating wrote:
How would you say that the JM Racing mods changed/improved the power and powerband?? And, there's not much better than the sound of a finely tuned...
How would you say that the JM Racing mods changed/improved the power and powerband??

And, there's not much better than the sound of a finely tuned 2 stroke on the pipe....!!!!
The entire power band is much more broad, and over-rev is much improved. I use to have a dead spot between 3rd and 4th.. it'd run...
The entire power band is much more broad, and over-rev is much improved. I use to have a dead spot between 3rd and 4th.. it'd run outta steam up top in 3rd, and I'd have to shift to 4th, but it would fall off a bit.

Now I just leave it in third. If I DO need to hit 4th, it now has the stones to pull it.. gap is gone.

I can't emphasize what a difference these mods made.

Freakin' fantastic 250-
What Mods did JM make on it?

Post a reply to: '17 '18 250SX JM Racing Performance build

The Latest