Help with a 125

SoonerRacer

New member
We are running a stock 1999 yz125, we can't get the motor to turn more than 8900 rpm's no matter what gear or gear ratio we try, I don't know what the max rpm is but I know most are turning their motors around 11-12,000 rpm, so what could be causing this?
Also having carb, I assume the carb is probably the original stock carb, having overflow problems, it constantly has fuel coming out of the overflow from the float bowl, float has been adjusted but doesn't seem to help, I've been told that the carb could just be wore out, if I replace it would it do any good to go with a bigger or ported carb since the motor is pretty much stock? Any tips or suggestions would be greatly appreciated.

Thanks!
 
I would guess you are running a fuel pump to the carb and you didn't change the float needle seat to restrict fuel pressure so you are flooding the carb since you are pushing fuel out the overflow. Ben Hurr on here and makes the new seats for PWK AirStryker.
 

Freezeman

Premium User
If you don't all ready have one install a y fitting before the fuel inlet of the carb and rout a return line back to your fuel tank.
 

46&2 racing

New member
In addition to all said above about the carb. - every single time I started chasing gears to get the rpm's up - my motor was tired. Freshen the top end and see what you get. I started putting a new piston and rings in every four nights and never had that problem again.
 
no, if Im not mistaken, Bruce runs at a gas only track ... how u been bruce ?? Hows val ?

good to see you are still in it
 

46&2 racing

New member
Hey Mark - Been Great....Val's in a 500 now and doing pretty good. One of my other boy's started this year too - in a 500 also - we're having a blast!
Good to see Josh moved up this year as well. Looks like you guy's are still having fun.
As far as the 125 stuff....We ran 110 octane at about 45:1 no alcohol. Spewed it through a 38mm Airstriker with a skinny jet. If we didn't run high 12's in fifth gear out of six, it was time for new stuff. Some guy's would have only replaced rings but I figured as long as I'm in there......
You HAVE to run a restricted return in the fuel line back to the tank - When you don't if your float needle and seat are weak or out of adjustment it'll **** out the over flow, if they're not weak they will be soon without the relief line. Restrict it however you want but I went about 2 to 3 sizes smaller than my main jet using a jet in the line.
Reeds also play a big part - No matter how tight the top end is, if your reeds aren't right you wont get the spin you want.
By the way - in a 125 you should turn 12K easy on a track - I always shot for more
 
Last edited:

tom_oneil

New member
We banged 13500 more than once on our 2000 YZ. Assuming the wiring, coil, coil wire & timing are good, I would also look real hard look at jetting & fuel system. First pull the plug and put in a fresh one. Take a minute and go over the coil wire connections on both ends with a magnifying glass if you have to.
Then using one of the above suggestions cut down on the amount of fuel you're feeding it. What temps are you seeing for water, EGT or head?

A real quick & dirty test would be get in the kart and start running, then shut the fuel off. If it takes off like a rocket for a few seconds as it runs out of fuel it's too rich.

Note - I have fought similar issues on 2 strokes and prolonged my agony by not changing plugs almost between every test. A fouled plug may not be visible to the naked eye and can cause the same symptoms.

If none of these have any effect throw a set of reeds at it.
 
Top