engine mods? low-end power

[sparkysakitas]

get them right here
http://www.mxsouth.com/renthal/rent...nt_sprockets_yamaha_sprockets_125cc-250cc.htm

 

[IndyMX]

Yup, haha, just follow the chain from the back sprocket and it loops around the front sprocket, very small compared to the rear. They can be a pain to get off though, i still can't get mine :whoa: But ya, 1 tooth on the front sprocket is equal to 3 or 3.5 on the rear, so -teeth on the rear for a litte bit better lower end, or get a front sprocket a size or two smaller for quite a bit better lower end (they're cheaper than rears too!). Ya, just need to experiment with the gearing, just like you have to with jetting which is a pain.. Goodluck! i hope all goes well for you! :cool:

Just to clarify... a 1 tooth DECREASE in size on the front is equal to about 3 tooth INCREASE in the rear.

 

[NM_KDX200]

I suggest a flywheel weight. It won't increase low-end power, but it will keep the bike spinning longer and give you the impression of more low end power, pretty much the same thing as the sprocket change really. All the sprocket change does is let you run at higher RPM, but lower speed- doesn't actually change the ENGINE one bit. Porting, on the other hand, will change the engine as will a pipe. Put it all together: pipe, porting, flywheel weight, and gearing and you can make a 125 a little more grunty. However, by the time you do all that you might as well do what I did and that's go buy a KTM200. :) Personally, on a 125, I'd skip the porting and go with lower gearing first, the flywheel weight next, then a torque pipe/silencer. Unlike porting, all of these are easily reversible should you decide to hit the MX track instead of the woods. In fact, if you just swapped the stock or a rev pipe for the torque pipe, you'd be good to go.

Oh, and keep the reeds fresh- on your bike, consider a dual-stage reed if you can find one. Dual stage made a sig. diff. to the KDX's low end.

 

[Sand_man]

right now i have 15f / 47r teeth on the sprocket, whick is this, low-end, or top-end? would this cause the bike to not take off fast, because when i try to use the clutch at all to take off fast the thing almost stalls, and if i start up the bike at the bottom of a hill and try to ride up it right away, it stalls, like its like its starting in second gear, is this because of the sprocket? thanks

 

[mtk]

That sounds like "top speed" gearing to me.

 

[250racing]

right now i have 15f / 47r teeth on the sprocket, whick is this, low-end, or top-end? would this cause the bike to not take off fast, because when i try to use the clutch at all to take off fast the thing almost stalls, and if i start up the bike at the bottom of a hill and try to ride up it right away, it stalls, like its like its starting in second gear, is this because of the sprocket? thanks

try to find out first the gearing the bike came with i think somebody really messed up the gearing. try getting those sprockets and maybe a 1 tooth smaller front sprocket and test it.

according to renthal your standard setup would be 13-51

http://www.renthal.com/cw_master_page.asp?make=1

if your gearing is what you report it would be like starting in 3rd or 4th gear with the 13-51 gearing so going to a 13-51 or 13-52 will definately wake up your bike although your bike will have a lower top speed.

imagine your bike has now 3rd to 9th gears instead of 1st to 6th gears with the current sprockets.

 

[sparkysakitas]

stock for 90 yz is 13-50
same as my 96 yz
i went to 12/50
and like i said earlier it woke mine up although you do have to shift more

for +/- 100$ you can get new front and rear sprocket and decent chain

 

[Sand_man]

yea, thats exactly how it felt, like i started in 2d or 3d gear, so i hope 13-51 will help. Thanks for the help guys!

 

[Sand_man]

would a 13-49 be ok? i found a kit that came with front-13 rear-49 and a new chain. i couldnt find the stock 13-51. Thanks

 

[250racing]

it will be better but not optimal you could always buy a 12t front sprocket to test with the 49 rear sprocket and it shouldnt be more than 10 to 15 bucks.

keep us updated.

 

[Sand_man]

will do, thanks! ::UPDATE:: i found a place where i can order 13/51 this morning. so thats good, but will i have to buy a new chain?, or could i use my old one?

 

[250racing]

i would also buy a chain because the older chain has already taken the shape of the older sprocket teeth and it will prematurely wear your new sprockets.

if you can also get some new boyesen reeds the cheapest two stage ones give great torque to the engine.

 

[Sand_man]

what are reeds?

 

[250racing]

what are reeds?

the reeds is a part that is between the carb and the cylinder they allow the fuel to get into the cylinder and they are a wear item that should be replaced every year or performance will drop.

try www.boyesen.com dont get a rad valve as they are expensive just the replacement 2 stage reeds for your stock manifold.

 

[Sand_man]

ok, thanks!