KTM 300 kit worse for MX - recommendations?

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10/13/2018 2:16 PM

My father and I picked up a 2018 KTM 250 and he immediately orders a 300 kit to make it more "tractor like" as we're coming off racing 450's.

The bike was barely ran in before the 300 kit was installed and, whilst I've been pretty happy with the bike, reading this forum I was surprised to see that few fast MX guys run the 300 so decided to put it back to stock (to my father's annoyance).

The bike rides SO much better, revs more freely and hangs onto gears longer. I can clear jumps easier and the already light bike feels like an e-mountain bike now.

Does any recommend any mod's to the stock 250 engine/carb? I've seen a few mentions of lectron etc in the past...

Incidentally I have the 300 kit for sale if anyone wants it for woods, trail riding. Less than 10 hours on it.

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10/13/2018 2:19 PM
Edited Date/Time: 10/13/2018 2:20 PM

Set the head height using the different thinkness base gaskets that KTM offers. I’ve been out of that game for a while, so consult an expert - but setting that height just right and running some good clean fuel will go FAR

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Washed up moto and enduro weekend warrior.

10/13/2018 2:36 PM

yeah, get a Keihin taper bore 38/40mm carb with STIC if you really want it to scream. (so happen that I have one avaiable, 4 hours use)

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vomiting equals disqualification.

10/13/2018 2:37 PM

MXA summed it up well when these 300SXS kits first came out when they describe it as an angry 250. A lot of people think the 300 kit is going to make it more like a thumper, but my experience mirrors what MXA said.

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10/13/2018 2:55 PM

300XC=Tractor with low end grunt and torquey power delivery

300SXS=Runs like a screaming banshee with unreal overrev

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If it can't be fixed with a hammer, it's an electrical problem.

10/13/2018 2:58 PM

T-Fish wrote:

MXA summed it up well when these 300SXS kits first came out when they describe it as an angry 250. A lot of people think the 300 kit is going to make it more like a thumper, but my experience mirrors what MXA said.

Sounds like a flywheel weight would be a better mod for that purpose.

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10/13/2018 3:03 PM

I have a 300 XC with a lectron, FMF, 250 XS cdi. And the thing rips way better

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10/13/2018 3:12 PM

Get a 300 sx CDI from Slavens for $150 and make sure the airbox is opened up a bit and she'll scream more like a 250. Probably not worth the hassle if you've already switched back though.

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2019 TX300
'10 200 XC-w

10/13/2018 3:15 PM

Good on you for realizing the 300 is not a good MX modification. The 250 more free-revving nature is generally much preferred for motocross to ensure you have the top end needed to clear jumps. Personally, I would not go with a Lectron either as it too is best for the trails and offroad. Just get a Pro Circuit shorty to expand the over-rev even more and then leave the engine stock.

Spend your effort in jetting the bike properly and getting the PSI setting for your weight/speed and adjusting the clickers. Save your money on proper maintenance.

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10/13/2018 3:19 PM

tk2stroke wrote:

Good on you for realizing the 300 is not a good MX modification. The 250 more free-revving nature is generally much preferred for motocross to ensure you have the top end needed to clear jumps. Personally, I would not go with a Lectron either as it too is best for the trails and offroad. Just get a Pro Circuit shorty to expand the over-rev even more and then leave the engine stock.

Spend your effort in jetting the bike properly and getting the PSI setting for your weight/speed and adjusting the clickers. Save your money on proper maintenance.

Shorty silencers are worse for over rev. You guys must be damn picky. My 300 is awesome on the track. Everyone who has ridden it says the same...two of my friends are selling their 450’s to buy one after riding mine.

How the hell are you having trouble clearing jumps? Just shift it, and she pulls.

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Tomac and/or Anderson for 2020.....

10/13/2018 3:47 PM

BobPA wrote:

Shorty silencers are worse for over rev. You guys must be damn picky. My 300 is awesome on the track. Everyone who has ridden it says the same...two of my friends are selling their 450’s to buy one after riding mine.

How the hell are you having trouble clearing jumps? Just shift it, and she pulls.

"Shorty's are worse for overrev". where did you come up with this? The entire 2-stroke racing community have been using shortys for decades for maximum power and overrev qualities, this is undeniable fact.

And heck no, short shifting is not a wise practice for moto for several reasons and especially not on jump faces.

I do know some vets who claim to love the 300 for moto, but overwhelmingly the 250 is the preferred engine platform. I've ridden both extensively in moto, trails, and desert, and like the OP realized, the 250 is the better platform for any type of riding where there are higher speeds and top end is preferred. For slower gnarly types of riding, the 300 is generally preferred. You may not agree and to each there own, but this is not the popular consensus.

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10/13/2018 3:50 PM

We have 4 TM 300's , they are built to be a 300 and work very well. We tried to to take one out to 344 by boring and stroking , but got as far as 330 and it just didnt work for Supermoto, the bigger piston and longer stroke just didnt want to rev, and so it wasnt really a benefit..

From the sound of it, the KTM doesnt like going bigger either,

I did hear that a lot of the EMX300 guys were running 250's , and the guys running Yamaha's who went big struggled as well.

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10/13/2018 4:22 PM

I remeber Ryan Sipes mentioned he had a 300 at last years rb straight rhythm, said he wished he ran the TC250 instead

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10/13/2018 4:27 PM

I haven't tried it but I've been told the RK Tek gives huge gains.

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Care Factor Zero

10/13/2018 4:40 PM

tk2stroke wrote:

"Shorty's are worse for overrev". where did you come up with this? The entire 2-stroke racing community have been using shortys for decades for maximum power and overrev qualities, this is undeniable fact.

And heck no, short shifting is not a wise practice for moto for several reasons and especially not on jump faces.

I do know some vets who claim to love the 300 for moto, but overwhelmingly the 250 is the preferred engine platform. I've ridden both extensively in moto, trails, and desert, and like the OP realized, the 250 is the better platform for any type of riding where there are higher speeds and top end is preferred. For slower gnarly types of riding, the 300 is generally preferred. You may not agree and to each there own, but this is not the popular consensus.

I dug up a thread where a guy asked FMF why his bike didn’t have much over rev. Here was their reply:

To Whom It May Concern:

Thanks for contacting FMF Racing. The SST is meant for top end power but your Shorty silencer is meant for bottom end power.

We suggest changing your silencer to a Powercore 2 which makes great power through the mid and top end of the RPM's.

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10/14/2018 7:16 PM

I have a Lectron on my 250 sx and I couldn't be happier! Completely cleared up my jetting issues and the thing revs to the moon. You wouldn't regret buying one!

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10/14/2018 9:01 PM

The Dicks Racing carb and head mods make the 300 better for everything.

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10/14/2018 9:59 PM

The only thing you need on it is a HGS pipe. It will open up the top-end even more.

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10/15/2018 2:37 AM

Are you sure the z height is right? And the red spring all out an 1,5 in??? Which pipe? My 300 is better all over.

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10/15/2018 5:45 AM
Edited Date/Time: 10/15/2018 5:46 AM

Mine isn`t as new as yours . But i run 38mm smartcarb, Pro circuit pipe , and shorty silencer. Red exhaust spring

The stock exhaust felt too chocked up to me , compare to the Pro Ciruit system.

it isnt as light in the rev as a 250 but i can pull the rev pretty high

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10/15/2018 6:26 AM

As mentioned in one post. There are two 300 barrels (porting) available. EXC and SX. Also two ignitions to match I believe. Some of the above comparisons are Enduro to MX spec.

As mentioned there are a lot of other factors: carb/jetting, pipe/silencer, head/squish and ignition.

One story in MXA suggested an SX barrel conversion, fully set up MX style is too much for all but the fastest pro.

Personally, if I was going this way, I’d go the EXC barrel, and tune it UP from there, if required.

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10/15/2018 9:05 AM

tk2stroke wrote:

"Shorty's are worse for overrev". where did you come up with this? The entire 2-stroke racing community have been using shortys for decades for maximum power and overrev qualities, this is undeniable fact.

And heck no, short shifting is not a wise practice for moto for several reasons and especially not on jump faces.

I do know some vets who claim to love the 300 for moto, but overwhelmingly the 250 is the preferred engine platform. I've ridden both extensively in moto, trails, and desert, and like the OP realized, the 250 is the better platform for any type of riding where there are higher speeds and top end is preferred. For slower gnarly types of riding, the 300 is generally preferred. You may not agree and to each there own, but this is not the popular consensus.

its a proven fact that shorty silencers add some bottom end and cut out some top end over rev. Why do you think Travis had that long ass silencer on his RM250 at the MXON? Longer stingers/silencers add to over rev and smooth the power out somewhat.

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10/15/2018 9:26 AM

tk2stroke wrote:

Good on you for realizing the 300 is not a good MX modification. The 250 more free-revving nature is generally much preferred for motocross to ensure you have the top end needed to clear jumps. Personally, I would not go with a Lectron either as it too is best for the trails and offroad. Just get a Pro Circuit shorty to expand the over-rev even more and then leave the engine stock.

Spend your effort in jetting the bike properly and getting the PSI setting for your weight/speed and adjusting the clickers. Save your money on proper maintenance.

BobPA wrote:

Shorty silencers are worse for over rev. You guys must be damn picky. My 300 is awesome on the track. Everyone who has ridden it says the same...two of my friends are selling their 450’s to buy one after riding mine.

How the hell are you having trouble clearing jumps? Just shift it, and she pulls.

tk2stroke wrote:

"Shorty's are worse for overrev". where did you come up with this? The entire 2-stroke racing community have been using shortys for decades for maximum power and overrev qualities, this is undeniable fact.

And heck no, short shifting is not a wise practice for moto for several reasons and especially not on jump faces.

I do know some vets who claim to love the 300 for moto, but overwhelmingly the 250 is the preferred engine platform. I've ridden both extensively in moto, trails, and desert, and like the OP realized, the 250 is the better platform for any type of riding where there are higher speeds and top end is preferred. For slower gnarly types of riding, the 300 is generally preferred. You may not agree and to each there own, but this is not the popular consensus.

It is actually fact that that shorty silencers are better on the bottom and a long silencer allows the bike to rev out further. Please get your ducks in a row and don't call out info as fact when you are completely 180° the wrong direction. Most people just run the shorty because it makes them sound faster. Just like all the people talking about pastranas silencer at Des nation's. In addition to needing to pass sound, it needs to be that long for a proper outdoor setup.

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10/15/2018 10:20 AM

tk2stroke wrote:

Good on you for realizing the 300 is not a good MX modification. The 250 more free-revving nature is generally much preferred for motocross to ensure you have the top end needed to clear jumps. Personally, I would not go with a Lectron either as it too is best for the trails and offroad. Just get a Pro Circuit shorty to expand the over-rev even more and then leave the engine stock.

Spend your effort in jetting the bike properly and getting the PSI setting for your weight/speed and adjusting the clickers. Save your money on proper maintenance.

I think you're the only one that doesnt know shorty silencers are better for bottom end snap as they take away some on top end overrrev as a tradeoff.

I rode a 2014 KTM 300 (offroad version w/o the headlight) and it felt like a good running 250, yes it pulled just slightly harder through the mid range and was smooth but compared to any 250 2 stroke mx based bike it wasnt as snappy and quick/free revving.

If the OP was still looking for mods for his 300sx, by now he'd surely be confused as hell. It seems everyone has a different idea on what to do to maximize the engine output for riding mx lol

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10/15/2018 4:13 PM

I do stand corrected. Get the shortly nonetheless, it does sound better and the 250 still has more over-rev than a 300 and is a better all around mx'er.

From my own experience, the shorty provided more power and top end, but in all those cases I was coming off the longer stock silencer.

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10/15/2018 5:02 PM

SeaClassExpert wrote:

300XC=Tractor with low end grunt and torquey power delivery

300SXS=Runs like a screaming banshee with unreal overrev

This. The sx crank is lighter and the sxs kit i believe is higher comp. i think the cdi’s are the same. Its really the lighter crank that allows it to spool up faster making it more 250 like with power everywhere.

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10/15/2018 7:33 PM

tk2stroke wrote:

I do stand corrected. Get the shortly nonetheless, it does sound better and the 250 still has more over-rev than a 300 and is a better all around mx'er.

From my own experience, the shorty provided more power and top end, but in all those cases I was coming off the longer stock silencer.

The shorty does give the powerband more of a 'hit', so you may have felt like it had more top end, but the longer stock silencer will provide more over-rev. In other words - you don't have to shift as soon before the power flattens out.

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