Lacking low end power?

[jtimpano108]

Looking for some tips I’m pretty new to 2 strokes...I just picked up a 97 rm125 for a steal but it was a mess no power no power band the power valves didn’t work the bike ran extremely rich and bogged it would idle or start without 1/4 throttle after lots of looking on forums and such I figured out a lot of good stuff first thing was fixed the power valves so my first question is with the adjustment on the power valves will more spring tension cause more low end power or will it give a later power band? Currently the bike runs a lot better it will start first kick and idle with no throttle input it revs up nice without bogging after I rejected the carb (170 main, 50 pilot 2nd clip position) these are recommended by pro circuit for their exhausts which is what’s on the bike now the bike has power won’t bog out at top end throttle but it seems to hit the power band a little late and also seems to be lacking power in the low end in first at full throttle the bike won’t lift the front tire off the ground I’m thinking the bike is still a bit rich? As I lean the bike out using the air screw it runs better it’s currently 4 turns out which means leaner jets I guess? Which jet should I bump down and what jet would be causing lack of low end power as I leaned the bike out with the Air screw it seemed to get a bit more power and eliminated the pop and bog at full throttle...any input would be appreciated thanks everyone

 

[Okiewan]

Couple things:

1) Power valve adjustments can't make MORE power
2) A heavier spring will increase the "hit" as it'll delay opening.
3) Fiddle with it too much and you'll risk messing up the port timing
4) Pro Circuit or anyone else for that matter, offers a BASELINE jetting suggestion. It doesn't account for (your) altitude, air temp, fuel, etc. If you happen to live near PC, you're good to go. :)

Your best bet is to set the PV per the manual and ride it.

 

[jtimpano108]

Couple things:

1) Power valve adjustments can't make MORE power
2) A heavier spring will increase the "hit" as it'll delay opening.
3) Fiddle with it too much and you'll risk messing up the port timing
4) Pro Circuit or anyone else for that matter, offers a BASELINE jetting suggestion. It doesn't account for (your) altitude, air temp, fuel, etc. If you happen to live near PC, you're good to go. :)

Your best bet is to set the PV per the manual and ride it.

So I read what you said and I read the manual I got the power band so it hits a lot sooner because it was hitting almost halfway through the gears before now it opens pretty soon but the bike hits the power band or at least tries and then just sits at that “power” and bogs and sputters the more I lean the bike the better it gets but I got to 5 turns out on the carb adjustment and can’t do anymore so way to rich? What jet and how many steps down should I go?

 

[Okiewan]

Fist thing you need to do is understand jetting and how the circuits work together.
Read this (several times): How-To - KDX - Motorcycle Carburetor Tuning . Don't worry that is says "KDX" it applies to everything.

 

[jtimpano108]

Fist thing you need to do is understand jetting and how the circuits work together.
Read this (several times): How-To - KDX - Motorcycle Carburetor Tuning . Don't worry that is says "KDX" it applies to everything.

What confuses me with my bike is that the more I lean the carb using the air screw the better it gets but I’m not having trouble with the bik at 1/4 throttle I’m having trouble at 3/4 to full throttle which would come to the main jet but from that article it seems that the Air screw doesn’t even do anything to the main jet?

 

[jaguar]

the idle circuit is always in play, it's just that at WOT its influence is very little.
The tuning sequence is set the idle, main, then needle height, then possibly change the slide cutaway. My write-up on the subject is at 2 Stroke Carburetor Tuning
And if you can't get it right no matter what then it's probably time to change the crank seals.