tuning 98kx 125 carb

[gargamel6]

My buddy has a 98 kx 125. I am trying to get the jetting correct on it. Here is what it is doing...If you roll on the throttle slowly it runs fine. If you quickly go from closed to 1/2 to 3/4 it boggs and wants to cut out. Hills...forget about it. Carb is at factory settings. We aren't small guys (200lbs.)..he's just new to bikes and we thought this would be good to start on, maybe it wasnt the best idea! It has a pro circuit platnum pipe/ silencer. The pipe seems to be the only aftermarket thing on it. previous owner didn't change any jetting...does that make sense? So far I have adjusted the float (so it will stop pissing) and inspected the float valve, looks OK.
This is the first 125 I have ever ridden, could it be that it is normal to act this way with a big rider? If this is the case, could a sprocket change help..not worried about top speed at this point!
Is there an easier way to check jetting than doing throttle chops? Do I have to be in 4th or 5th gear to do them for the main jet? I mean couldn't I just be in 1st WOT and get the same results? finding a wide open area to do it is kind of tough for me.
Alot of questions I know...The more I read the more questions I have!!!
Thanks for input

 

[KX02]

Before you start messing with the carb it would be good to know the condition of the motor. If the top end is shot there is no point in playing with jets. The best way to jet the bike is to start with the low speed/pilot circuit and work you way up. Do a search and you will find tons of material. Good luck!

PS I see you also have a 2005 KX250. How do you like it? I love mine, wish I could get out to ride more!

 

[gargamel6]

The previous owner did a complete rebuild. I don't have any reason to not believe him...yet. How could I tell, compression? I am trying to nail down the slow jet now. I get it to a fast idle and adjust the air screw. I thought it would be easy to find the sweet spot, maybe I just havent turned it enough yet. I'm gonna mess with it tommorow. I'm pretty sure it's a little rich because it's like a spooge factory!
Love the KX 250. It had some jetting issues off the bat, guess they are pretty fat from the factory. Got the JD jet kit, cant say enough about it.

 

[gargamel6]

Ideas, anyone....anyone....
The more I look at this forum the more I wonder if it could be something other than jetting. I read a few threads about the power valve. Seemed like the symptoms were similar. I really am itching to get into it, but we don't yet have a manual for it. I took the cover off that exposed the actuator arm(right term?) for the power valve. It was in the down position. I took the arm off and moved the valve, it moved more or less freely. It kind of hung in the up position a little. The gears look goood. I put the arm back on and moved the arm. It springs back to the down position without binding. So for now I am dismissing this as a problem...like I said, don't yet have the book! I just don't know. Not having ridden a 125 before doesn't help. without a load I can open the throttle and there seems to be no problem. With me on board quickly going from closed throttle to 1/2 or 3/4 it wants to sputter out and die! maybe it's just the "fat guy on board effect." Hopefully tommorow I will have time to look at it, and hopefully someone will have some insight.