KTM125SX - Where's the low end???

[ToddHawaii]

While my bike is being rebuilt, I have decided to ride my wife's bike - an 04' KTM125SX. I ride the more difficult trails here in Colorado, so I set out to make her bike a little more "trail-worthy." Skid plate, bark-busters...even a 9oz. flywheel weight. The gearing is 13/50.

I know, I'm lame for asking :whoa: but, my question is - why does the bike still bog when I hit the throttle? Like to simply bop over a root, or rock? Is my gearing off? I've ridden Yamaha and Suzuki 125s without noticing this lack of low-end. As soon as I'm in the power, it's fine. Is it just a matter of learning to stay in the power-band? Or, should I up to a 12t counter, or a 52t rear sprocket?

Also, this bike only has 5 gears, instead of the 6 that I thought it was supposed to have. Any answers here?

Thanks for your help!!!

 

[Krossipoiss]

I suspect wrong jetting.

 

[ToddHawaii]

Really? Okay, again showing my ignorance, so even though it runs like a banchee all the way through the power band, my jetting might need adjusting? Like moving the clip up or down on the needle?

Thanks!

 

[_JOE_]

It's a small bore race bike. It is tuned for top end. The best solution to move the power(assuming the jetting is as good as you can get it) would be to have the cylinder porting altered. Aside from that you might be able to improve it with a different reed setup or exhaust system. Your bike should also have an adjustable power valve you can use to help fine tune the "hit" once you get it jetted and what not. Timing can also be altered to change the power in most cases, though I wouldn't suggest that unless you feel confident you know what you're doing.

 

[_JOE_]

And yes, the needle clip position is what you use to tune the midrange. You should make sure the float height is set coorectly before jetting. Here's a link to a good jetting guide.........http://www.dirtrider.net/forums3/showthread.php?p=1340315#post1340315

 

[ToddHawaii]

Joe - excellent! I'm on it!

Thanks!

 

[mdavidso]

Also to what has been said, you might want to get a boyesen RAD valve, got one for my '03, made a huge difference!

 

[miles11we]

you may just not be riding the engine right, 1st you put a flywheel weight on a 125, witch would make it more likely to bog and more resistant to rev quickly. 2nd stay in the power band!!!!! it isnt that hard just takes more shifting, 125s make most there power from the pipe and wile on the powerband, this means if ur not on the pipe at all ur just using the power of a small engine that (because its a two stroke) wont have alot of torque off the powerband.... its not the bike its your riding style, just try to stay on the powerband

 

[tyler_43]

I would try the 12tooth front sprocket... when I used to bush ride 125's I always had them very low geared and did NOT use a flywheel weight... that way i could crack the throttle and the revs would snap up allowing me to get over logs etc. My yz125 was a 5-speed as well and with the low gearing it only did about 60mph :P
Little bursts of clutch help too... that and tires... on the motocross track I never felt a big difference between tires, but having too big a tire on my 125 in the trails really bogged it down. These are all cheap alternatives to things like porting, which if you have the budget will REALLY help out in the trails.

 

[explorer]

Set the powervalve to its lowest setting.
That will improve lowend considertly.
and check yr squish gap. go for the 0.9mm gap. High compression is yr friend.

 

[Pete Payne]

The bog is due to the air screw setting . That is as long as the rest of the engine is in good shape, air filter is clean etc.
The flywheel weight will not make a bog , it will cause the engine to rev up a little slower due to the extra mass the engine has to turn.

Dive into the carb and get it right .

 

[DEANSFASTWAY]

Petes probably right but the power valve adjustment on the rs of the motor has a big affect on these SXs espescially of too tight it wont let the PV open which would kill the top end I had one in my shop where a dealer sold him a 200 CDI after they couldnt figure it out. You might wanna try one of those airfoil thongs in the carb like a power now device it divides the carb venturi in half for more air velocity Ive seen other guys take a very small drill and drill a tiny hole on the shrouded protruding area of the main get nozzle (the part that sticks up when looking through the carb from the back if all this is unfamiliar to you dont bother . Man that 125 has a big carb on it. if youre i real high elevation you might wanna run thinner base gasket like another guy said compression is your friend. Start with the carb like Pete said though no matter what you do though its not gonna hop over logs with a blip of the throttle