From Let’s tame this engine as part of our motocross to enduro bike conversion for the KTM 250SX. This is usually by far the biggest issue with this type of conversion. On the first ride I was having so much trouble on our steeper tight tracks I put on the G2 throttle tamer. At US$70 this made a big difference immediately. It uses a cam to make the first half of the throttle open slowly, then the second half quickly, which allows us gumby riders to have far more control at smaller throttle openings. See our Throttle Tamer review.

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Bang for buck we figured the next best mod would be the Steahly flywheel weight for US$130. This reduces the snappy engine response, makes the bike much less likely to stall, smooths out the power delivery and helps to get traction. It came with good instructions and even a gumby can fit this in thirty minutes or three beers, whichever comes first. We went for the 12 ounce flywheel weight which seems to be the choice for these motocross enduro conversions. A quick test after fitting? Wow. Just as described. Suddenly I wasn’t stalling the bike, and the rear wheel wasn’t spinning the moment I touched the throttle. I can see why a lot of riders put these on enduro models too, and how they would especially suit less experienced riders. It seems though that motocross riders use them too, just pause to read this info from the Steahly website.

A cheap easy mod with the KTMs is just changing and adjusting the power valve spring, which we covered in the previous video. I took out the aggressive red spring and put in the much milder green spring which means it takes longer for the powervalve to open. I also set it to open earlier and hopefully broaden that surge of power. It’s worth experimenting here, there are some riders who keep the aggressive red spring and prefer that rush of power around 6000rpm.

We threw in the Suzuki NECJ needle, this provides smoother power at low revs, less chance of fouling plugs and less spooge out of the exhaust.

There are more mods for a motocross to enduro conversion, but this is where we stopped with the KTM 250SX.

For riders who like tinkering, a different exhaust like the FMF Gnarly will give more grunt and knock a bit off the top end power.

You can use the 250EXC cylinder head, CDI and muffler to soften the power delivery. It’s often easy to arrange a swap with a 250EXC rider who is chasing more power.

You can have the cylinder head reshaped, fit low tension reeds, change the porting, or change the base gasket to change the compression.

EXC head
EXC muffler
Low tension reeds
Base gasket

Pete took the SX for a ride and agreed it definitely had more power across the rev range than the EXC, the throttle response was faster and the power came on more aggressively. His verdict? Great for the experienced rider, and I would tend to agree. For guys at our level and style of riding, this sort of power can fun but we will be faster and safer with the more gentle power of the EXC. I also got one of our other guys to ride it and he was grinning ear to ear when he got off it. But he did admit despite loving the power he probably would wind up hurting himself. I tend to agree!

What else? It has to be geared down, this 13 and 48 tooth sprocket setup is way too high and I keep bogging it down on our steeper climbs. And the suspension and tyres definitely need attention, we’ll look at all of these in coming episodes.


Sam Bott says:

How long do Kelly enduro products take to ship (inside australia.

Zane Zinn says:

a 85 is a bitch to ride on trails

taaviw126 says:

Riding slow is smooth and riding smooth is fast:)

george says:

Don’t be a bloke. Be a real man, and learn throttle control. Use the red spring. Haha but actually I prefer the red because of the fun factor. It might not be the best for technical sections but It keeps me grinning ear to ear.

Adam Horne says:

It really hurts my feelings that the world is in such a state that these awesome videos have 30,000 views, but my suggested videos are flooded with some prepubescent child doing wheelies on a dirt bike his parents bought him that have millions of views.

Jonny g says:

I’ll stick with my beta xtrainer ,I manage to crash enough on that so don’t need anymore power

Van Alstyne says:

Will a flywheel weight make the motor work any harder over it’s lifetime?

Gabriel Gauthier says:

Nice job! gotta love it

B Hartman says:

interesting ideas for sure! one thing i did on my 300 that i feel is a must is a jd jetting kit. made for spot on tuning without the guess work. should be interesting when ktm releases the injected 2t’s to see how they are tuned!

Aaron Maz says:

Well done. Love the sound and riding you do on a 2t. Gets the blood pumping.

ElectroMoto says:

How the hell do you NOT crash into foliage in these speeds?!.. I find myself constantly holding my breath at certain scenes…

Jamie Brasnyo says:

I’ve been riding enduro on a crf450x for years. It’s tough watching you guys fly up climbs and lift your front end like butter but it’s all I’ve ever ridden. Any ideas or mods for my bike aside from “get a different bike bro” to help it be more suitable would be great.

Liam Kendall says:

This is one of my favourite videos ever, I have always wanted a 250sx 2015 and was considering getting one. But I think I will wait to the end of the series before I do buy one to see whether i will change my mind.


Really excited to hear how you make out with the 4cs, I have been battling mine for two years now and have yet to take em anywhere

I'm riding a bsa says:

lov ur vids, keep up the good work.
personally I went 1 down on the front sprocket (12t) and a Gnarly pipe (does wonders for stalling),a map switch,(engaged for the straights), yellow ,then green, back to yellow Aux pv spring(screwed in 1 turn) (work in progress situation) and a Tubliss rear tyre. Now I grit my teeth an hang on.

MB Beard says:

Keep it coming!R/

salisburyplain998 says:

or you can stop wasting your time and buy a xtrainer .

Kevin Herndon says:

13-52 gearing mate.

J says:

I guess this is my answer, now to find a yz250 that’s not been rebuilt 10 times

Backyard Boosters says:

love it!

Elisa S says:

your just turning it into a 4 stroke…

charles cardery says:

Im doing a similar thing to my cr250

twelthmanfan says:

Just bought a 2017 Honda CRF250R and obviously it has too much throttle response and it’s too light to do well in tight technical and rough Terrain so I need to know what are a few mods I should do to smooth out the throttle response and make it easier to control for a new Rider

Rock Goons says:

i find the green pv spring to be easy to ride but extremely boggy(like at 6:25), and that’s 13:49 without a fww or throttle tube. i could need a top end by now though…
i plan to experiment with the yellow spring and a 10oz fww this season. green spring on a hill you need to finger bang the clutch, why not take some of the clutch work out with the yellow spring?
the red spring is fun, but only when it’s dry and not rocky.

also for OC forks it’s suggested 1-1.2mm of mv float with a dual stage bv for woods. idk anything about CC/4CS/AER forks

Glenn Edwards says:

Nice work! Go for 13/52 or 12/48 gearing!

Wide000 says:

I installed a Steahly flywheel on my exc 2005 250 too and it certainly improve traction and stalling, but it also makes for a slow throttle response. But the exc already have a heavier flywheel than the sx, so it is maybe a bit too much but it still is a good thing in tight areas. I use 13/52 gearing but I am not satisfied with the gap between the first and second gear. There is no cure for it, unfortunatly: wide ratio + five speeds only = bad engineering idea.

Brian Roberts says:

heeeyyy.. easy on us husky folks.. lol!

roflcopterkklol says:

You can just take the power valve adjustment spring out, i find all it does is limit the bottom end and mid range power and if you have an fmf gnarly pipe there is hardly any top end left anyway.

Zac Wilson says:

Hey there just wondering what carburettor needle did you use and jetting in the carb? Cheers

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