From http://www.crosstrainingenduro.com 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.
Low tension reeds
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.