engine mods? low-end power

[Sand_man]

i have a 1990 yamaha yz 125, im not sure if this is the place to ask, but it involes a 2-stroke. are there any engine mods i could do to help low-end power. the bike does great in top-end, but low-end is not that great. thanks
-Tony

 

[Oldman125]

FMF Fatty and silencer, gear down (add teeth to the rear sprocket or subtract one from the front). That should help.
If its not enough porting for torque will make a lot of difference.
Keep that in mind that 125s aren't low end engines however.

 

[Sand_man]

thanks for the help, is a 4-stroke good in low-end and top-end? or are they the same? thanks

 

[splatt]

thanks for the help, is a 4-stroke good in low-end and top-end? or are they the same? thanks

A 4-stroke will usually have a much broader powerband than a 2-stroke.

Steve

 

[emoguitar131]

Try playing around with your timing a little bit... I have a 93 KX 250 that when I bought it, was very quick but would fall flat at about 6000 RPM's. When I looked at the timing, I saw that it was fully retarded. Upon advancing, the bike absolutely rips now. :cool:

 

[sparkysakitas]

i dropped a gear on my yz from 13t to a 12t front and it helped a great bit down here got to shift more but on the trails its great (back is a 50t) also have fatty with stock silencer but it came on bike so cant tell if it had made difference

 

[Sand_man]

ok, thanks for all the help!

 

[Flygirl]

I'm just a beginner (started with a CRF230) and my husband wanted to get me a 2-stroke as well so he picked up an RM85L for me, did the porting to give it more bottom end (like a girl wants to hear she needs more bottom end...haha) and now he wants to adjust the sprocket....sure hope that will help me on the trails because this little bike is a go-getter and so much more fun than the 230. Are there other modifications other than what was mentioned and adding a fatty and silencer? I like the way the bike is as it sits other than trying to get out of a creek with a direct climb in front of me has been a challenge :-)

 

[rmguy125]

i put a fmf gold series fatty on my 04 rm 125 with a power core 2 shorty scielencer and it has extreme low end power

 

[Sand_man]

ok, i got a fatty on mine 2, but it is dented, will that cause anything?

 

[Zach_951]

It depends on the size of the dent and where at. The closer the dent is to the exhaust port, the more it will affect the power.

 

[Sand_man]

i dont know where the port is, but its very close to the front of the bike. how much will this mess with the bike? its a yz 125

 

[sparkysakitas]

where the pipe connects to the motor is the port

 

[Sand_man]

ok, so if its a big dent it will most likley not preform well? so will i notice a big diffrence if i put a new one on?

 

[Oldman125]

There is no detriment to performance with a small dent, even a larger one wont hurt much, according to test reports I've seen. However a crushed area will effect the wave reflection and cause a loss of perf.
Small dent? You're good.

 

[trial_07]

I've heard of a place that gets your pipe brand new for 50 bucks.

 

[monkeyonahill]

i've got an '01 cr 125r and i put a 53 T rear sprocket, FMF gold series fatty, a Powercore 2 silencer, V-Force 3 reedcage /reeds, and rejetted the carb and it's got great low end! :cool:

 

[sparkysakitas]

i run 12 tooth front and 50 rear ,have the fmf fatty,stock silencer
just need to re jet the carb but right now i got decent bottom
end on mine
i was amazed at the difference in the sprockets made
try that first see how you like it
as far as the dent goes if its not a bad one then i wouldnt waste money trying to get it out or by buying a new pipe
you can use the money on better things for now

 

[2wheels]

low end

Have Erric Gorr port it for low end. It is the most economical way to go.

 

[rmguy125]

yeah you will loose power through out the entire power band, that is the reason that i bought my fmf fatty

 

[Sand_man]

what do you mean about the sproket thing? buy a smaller size one?

 

[sparkysakitas]

what do you mean about the sproket thing? buy a smaller size one?

yes try one size smaller

 

[Sand_man]

will do, right now it has 53 teeth on it, what should i move down to? what do you mean when ppl say front-, back- i kno the back sproket, but therez on in the front?

 

[monkeyonahill]

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:

 

[Sand_man]

thanks for the good info!, now where could i get one that is smaller for the front or rear? i have a 1990 yamaha yz125, do i buy a stock sprocket off a yz100 or something? thanks!