RM-Z250 JM Racing build *up to Cams & Chassis talk*

Sandusky26
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Sandusky26 12/5/2021 2:36pm
12/5/2021 2:36pm
Keating wrote:
This yellow 250 makes great bottom end power!! NO bogging here either, ever!! I still have it on my list to try Deez387 gearing of a...
This yellow 250 makes great bottom end power!! NO bogging here either, ever!!

I still have it on my list to try Deez387 gearing of a 14/54. I've been running a 13/50 for most of my RMZ's life and like it just fine. The 14/54 will gearing will be ever so slightly lower, but dang near the same! I am hoping the chassis will free up a little more with the less binding ratio of the counter shaft sprocket to the transmission gears. I anticipate this to be most noticeable under acceleration when there is a load on the bike. My main issue is purchasing the sprockets and modifying the chain guide will be a little bit of a pain.... The good news is it's time for a new set of chain and sprockets now and I also have an extra Accerbis chain guide if I mess up the one on my bike! More on this to follow soon!
Will a 14 fit on your 250? I don’t think a 14 will fit on my 450 without removing the case saver. I have been thinking of doing the same thing to help free up the chassis. I seen on the JGR bikes they were using 13-50 on the outdoor bikes, I wonder what the HEP team uses for gearing.
250 cross
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250 cross 12/5/2021 3:14pm
12/5/2021 3:14pm
I ride a tight track so I like 13-52, pretty sure it keeps me from using second. I run the same gearing on my RM.
Keating
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Keating 12/6/2021 6:31pm
12/6/2021 6:31pm
Yes, I believe the case saver will need to come off. I already have taken mine off to prevent mud from packing in there.... It'll fit then since Deez387 has been running it for a while now. He had to modify the rear chain guide to give the rear sprocket room to fit without running the wheel all the way back...

I bet your bike picks up off the bottom really quick with that 13/52 on there "250 cross"....
bite_the_curb 12/7/2021 6:24am
12/7/2021 6:24am
do the 2012 showa twin chamber forks fit on these bikes off the rmz250 fit on these bikes?

ive heard alot of people dont like these forks even after the revalve.
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michigan906
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michigan906 12/9/2021 4:08pm
12/9/2021 4:08pm
Keating wrote:
I agree, the Suzuki is a beautiful bike! I love the way they look!! These are custom cams. Web can build you cams for different performance...
I agree, the Suzuki is a beautiful bike! I love the way they look!!

These are custom cams. Web can build you cams for different performance needs.... You send them your cams and they re-weld and grind them. Pretty amazing!

Thanks for the video. Derek is a buddy of mine and really great with GET ignitions. I'm going to get him to help me fine tune mine to get the most out of this little RMZ after I've got all these mods done and bring it all together!! Everything I've done has helped and made this RMZ250 better. I'm a novice with the ignitions and Derek is a Pro! He'll help me ice the cake and make it perfect!

Read the whole build if you haven't yet and see what will help your woods bike when you get it! Especially the Ride Engineering parts, they have made the chassis really handle well and JM Racing has got the suspension working excellent.
I agree, the RMZ250 will make an amazing woods bike...!!
michigan906 wrote:
He also has a video showing how good the RMZ can be with porting/cams/and ECU tuning, pretty cool video (you've probably already saw it). Looking forward...
He also has a video showing how good the RMZ can be with porting/cams/and ECU tuning, pretty cool video (you've probably already saw it). Looking forward to the outcome after you work with Derek. I think the Suzuki looks the best out of the other brands, but it is also the best sounding 250f in my opinion. You'll have to upload some audio clips of that beast when its all fine tuned.

I'm curious with the JM valving, did they use the stock pistons or did they put in race tech gold valves/or something equivalent in the front/rear? It's all KYB stuff so I know it can be made good with the stock internals. My only concern with the stiff chassis of the RMZ is getting beat up by harshness when racing close to a 3 hour harescramble. I would also plan on drilling the engine mounts and using less torque on the engine bolts like you did. The ride engineering link is something I would definitely try as well, did you have to change your spring rate to accommodate the RE link?

Id think with a revalve/respring, drilling the mounts, retorquing the engine bolts, that would be enough to make it comfortable/plush enough. There are also front engine mounts that I would be curious to try by Works Chassis Labs if it was still a little on the stiff side. https://workschassislab.myshopify.com/products/2019-2021-suzuki-rm-z250… . Have you thought about using those or know anybody who has and could feel the difference?
250 cross wrote:
In my opinion the chassis stiffness is a bit of an issue when it gets rough. I have changed my fork and shock springs twice now...
In my opinion the chassis stiffness is a bit of an issue when it gets rough. I have changed my fork and shock springs twice now, also had the forks revalved with lighter ICS. As a disclaimer I am 65 and ride on a no jump often groomed track mx track. Really fun bike on a groomed track, turns like crazy but when the decel and braking bumps get bad it's kind of evil. I also ride an 07 RM250 and 07 RMZ290 on the same track so I do have something to compare my 20 RMZ to. I'll have to say the suspension is much closer now but I do have the Works Chassis Labs soft front motor mounts on order. I'm willing to give up a little bit of the sharp handling if it softens the chassis a little.
Thanks to Seth505 for the advice on my second rear spring change, that was a huge help in figuring out what was going on with my unhappy corner approach.
Let us know what you think of the Works Chassis Labs softer motor mounts when you test them.
Coughlin639
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Coughlin639 12/10/2021 10:15pm
12/10/2021 10:15pm
The WCL mounts worked great in my 18' RM-Z 450. I'm an Am rider, so nothing special and I noticed a difference. Biggest thing I felt was more traction from the front wheel and less arm pump
Keating
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Keating 12/12/2021 8:16am
12/12/2021 8:16am
bite_the_curb wrote:
do the 2012 showa twin chamber forks fit on these bikes off the rmz250 fit on these bikes? ive heard alot of people dont like these...
do the 2012 showa twin chamber forks fit on these bikes off the rmz250 fit on these bikes?

ive heard alot of people dont like these forks even after the revalve.
Not sure man. There are a lot of factors to consider when making changes like that.... Not only fitting in the triple clamps and front wheel, but how long are the upper and lower tubes compared to the KYB. The action might be better on something like that, but will the flex in the fork make it handle better in choppy stuff, or big whoops, or turn differently, etc.
I drilled a 4mm hole in my engine hanger and could tell a difference in the handling... The engine mount companies are making little changes in thickness and shape of their mounts to noticeably change how the bike feels.... A great set of forks on bike X might mot work well at all on bike Y!
Just food for thought! If you have a set of those forks available, give 'em a try!! Let us know how they work. Good luck man.
Keating
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Keating 12/12/2021 9:38am
12/12/2021 9:38am
Coughlin639 wrote:
The WCL mounts worked great in my 18' RM-Z 450. I'm an Am rider, so nothing special and I noticed a difference. Biggest thing I felt...
The WCL mounts worked great in my 18' RM-Z 450. I'm an Am rider, so nothing special and I noticed a difference. Biggest thing I felt was more traction from the front wheel and less arm pump
Did you go with the upper and lower? Just the lower is available on the 250..... Bummer for me!!

MX Revival's video was pretty good. He seemed to think the mounts made a noticeable difference on his bike, although he was praising them after 2 corners of riding.

I am definitely adding them to the list of mods to try out and am going to order me some in the new year.
250 cross
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250 cross 12/14/2021 10:19am
12/14/2021 10:19am
I did install the WCL soft front mounts on my 250. They are beefier in section but also appear to be fully machined titanium instead of cast aluminum. Unfortunately there is frost in the ground now so no worthwhile testing until spring.
RiverockMX 12/14/2021 10:50am
12/14/2021 10:50am
Tend to be skeptical of professional YouTubers as so many things are overhyped. Odd that Pro team BarX Motorsports chooses to run stock mounts in the AMA Nationals. I'm sure they've put in the testing and could run whatever they like.
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250 cross
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250 cross 12/14/2021 12:07pm
12/14/2021 12:07pm
RiverockMX wrote:
Tend to be skeptical of professional YouTubers as so many things are overhyped. Odd that Pro team BarX Motorsports chooses to run stock mounts in the...
Tend to be skeptical of professional YouTubers as so many things are overhyped. Odd that Pro team BarX Motorsports chooses to run stock mounts in the AMA Nationals. I'm sure they've put in the testing and could run whatever they like.
BarX is likely running the stock mounts because they like the chassis as is, pro oriented which is too stiff for most vet riders. I'm changing the mounts to make it less like a bike a pro would ride and more like something an older rider can appreciate.
2
Sandusky26
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Sandusky26 12/15/2021 7:16am
12/15/2021 7:16am
I ordered 14/52 sprockets for my 450. Thats what Anstie was running in the nationals. My buddy loves 14/52 on his KTM 450. Thought about 14/53, but I find myself shifting to 4th gear really early coming out of corners.
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Coughlin639
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Coughlin639 12/23/2021 10:09pm
12/23/2021 10:09pm
Yes, I went with the Upper and Lower. The factory lower is like 11/16" thick. I even noticed a difference in vibration in the bike just by running the correct torque specs for the motor mounts though. I had reefed them down tight when I had the engine apart once. Then started reading how people were running reduced torque specs on the motor mount bolts. I think the KX450 or something is what I used and the whole bike vibrated less, so it definitely seemed to help me personally
Keating
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Keating 12/26/2021 8:00am
12/26/2021 8:00am
Coughlin639 wrote:
Yes, I went with the Upper and Lower. The factory lower is like 11/16" thick. I even noticed a difference in vibration in the bike just...
Yes, I went with the Upper and Lower. The factory lower is like 11/16" thick. I even noticed a difference in vibration in the bike just by running the correct torque specs for the motor mounts though. I had reefed them down tight when I had the engine apart once. Then started reading how people were running reduced torque specs on the motor mount bolts. I think the KX450 or something is what I used and the whole bike vibrated less, so it definitely seemed to help me personally
Yes, I too am running the KX lighter torque specs on the motor mounts. Some RMZ specs are a little lighter than the KX, like the front axle pinch bolts.... I'm running which ever spec is lighter on all chassis bolts. I put a mark on all the bolts to make sure they stayed tight and didn't work themselves loose and they never came loose. My combination of lighter torq and holes drilled in the engine hangers seem to help. I will try the other hangers and see if things get even better....
Sandusky26
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Sandusky26 12/26/2021 3:57pm
12/26/2021 3:57pm
I tried the 14/52 today and I’m impressed. The bike feels so much better coming into corners, it’s like it has no engine braking. I think your going to like the gearing swap, I’d like to know what you do to your chain guide for the 54 rear sprocket.
Lasse
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Lasse 6/18/2022 9:16am
6/18/2022 9:16am
How is this build coming?

I have an RMZ250 from 2019, that I got with a few extras. On top of that I just snatched a Rekluse autoclutch off of eBay for less than a quarter of a new one.

I tried a 13/52 based off of this thread, as I ride tighter “euro-tracks”, I think I felt I was running out of steam too soon as I am lugger at heart.

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