2005 KX250F Hitting rev limiter at 1/4 throttle

First and foremost hello everyone I'm Steve thanks for viewing and offering any helpful insight. A little background so everyone knows I bought this KX off craiglist for 800 bucks starts wont accelerate.

Heres the haves

After cleaning the carb thoroughly and reassembly problem still persisted so I proceeded with the following

removed cylinder head check that the piston was in the right direction

Checked valve clearance and re shimmed as needed

Retimed the motor

replaced the upper gaskets for air leaks

replaced both exhaust gaskets the one at the head and the one at the slip on

re built the carb all new gaskets, jets, needles. Settins are 42 pilot 180 main 3rd clip from the top on needle 50 leek

New Pro circuit aluminum hot start connector to carb sealed.

sprayed the motor with starting fluid to check for air leaks around the carb or gaskets

Here is my problem Bike fires instantly first kick every time choke on first start of the day never needed again. Idles like a pro idle and 1/8 throttle perfect as soon as you break 1/4 throttle it hits the rev limiter.... or so it sounds there is no way this is carb jetting or timing or clearance.

the muffler has 3, 1/4 size holes in it midway were some fat ass bottomed it out and hit the rear caliper. ( I believe them being in the muffler would not cause this ) I am leaning towards CDI or TPS maybe crank sensor anyone else heard of this seen it? Any ideas?

when you cleaned the carb did you take the tps off? its a star bit

No as I did not fully submerge the carb I only submerged it 3/4 of the way then sprayed it out with carb cleaner In the can before blowing it out with air. The basket was hung as to not let anything below the needle jet soak. I do have the torx bit capable of removing it. I also tried running the bike with the tps un plugged it fired and ran fine at idle but once again it wouldn't rev past qtr throttle without sounding like it hit the rev limiter.

my guess is that its probably just backfiring real bad making you think its hitting the rev limiter. Did you take a look at the accelerator pump diaphragm when you had the carb apart. I had a similar problem and the diaphragm was leaking.

New diaphragm I rebuilt everything in the carb.

The slide plate can be installed upside down in the carb and will cause very erratic running, most times the bike won't rev. That would be my first check. There is also a lower rev limit while in neutral so if it does it in gear that switch might be something to check as well.

can you get a video?

Got one on my phone how do I post it is it possible through the app?

Never took the slide plate off when I removed it

Here's the video one kick start choke off

Never took the slide plate off when I removed it

Doesn't mean it wasn't installed wrong before...... Never assume.

Here's the video one kick start choke off

?? Nothing

Did the video work?

Really cannot get video to load. I can email it.... Quick update checked the slide plate to manual it's on correctly. Checked the tps to the manual it's in the right voltage. Checked the stator ohms only because it won't rev high enough to check output. No short in the stator.

Make sure your crankshaft isnt twisted. Check TDC actual (piston location) and on the timing mark.

Just the final update pulled the exhaust muffler off all packing burnt off or taken out by previous owner. Basically like a short extended head pipe causing it to run way to lean re packed. Re adjusted carb to normal settings runs great. Thanks everyone for the help!

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now