Hello

First time poster, just bought a used KLX250S 2010 in Australia with 1500km.

Has cold start issues, requiring a blip of the throttle at the right time to get the bike running, it did have old gas in it though so that could of been the cause.
I decided it was best to go ahead and do the starter jet mod to eliminate any cold start issues from now on.

Pulled carb out and I can see the fuel idle screw plug is removed and the starter jet looks like it's completely open, no hole that needs to be drilled out. All the images I find depict a small hole on the starter jet smaller than .045 mm / .018. My one is completely open, I see some remnant of a lip inside the starter jet.


Pictures also show the shoulders of the brass Jets have been damaged, potentially overtightened.

Does anyone have advice on:

Is this normal?
How can I fix this issue?
What does this starter jet being drilled out mean for the running of the bike ?

Please see pictures attached

 

Surely I must be missing something in your description or in the picture. You say the "fuel idle screw plug is removed". Are you talking about the "mixutre screw" that is just out of the frame of the picture to the right? We can't see if the mixture screw is still there or not...it's out frame.

To be clear, let's go from left to right. The hole where the needle and seat is located on the far left is called the float valve seat. The next component to the right is the main jet. The next component to the right and slightly down in a recessed tube is the pilot jet. The next component to the right is the starter jet. The next component to the far right out of frame is the cast tube housing the mixture screw.

Your starter jet is still in place...see the round, brass piece with the hole in it. Now, whether it's drilled out or OEM size I can't really tell from the picture. It looks a little large from the pic, but my eyes aren't calibrated to your picture. The starter jet only functions when the choke **** is pulled/engaged, so for overall running of the engine, it will make no difference. If that brass starter jet had been somehow removed, we wouldn't see any brass color, and there would be nothing but a casting hole left behind. They are pressed in from the factory and not intended for removal. I think I can see that "lip" as you describe which might indicate someone drilled the starter jet a size up but didn't do all the way through to the bottom of the brass. The pic is not totally clear on this. Did you measure that starter jet hole to see what size it is? You can try some small drill bits to get an idea of the size.

On your comment about the jets being "damaged"...the somewhat rough common screwdriver slot in the pilot jet is pretty common and should not be a problem. That jet in particular can often be somewhat stuck in place on initial removal. The orifice opening looks fine to me...at least in the pic. The main jet looks fine too, but it's a little blurry in the pic.

Maybe I'm missing something else obvious in your description or the pic...which is possible.

 

Hello, thanks for the comment - I must admit it was late when I wrote this. I can confirm that I was mistakenly referring to the mixture screw as the idle fuel screw, I meant that I could see the plug that covers the mixture screw has been removed, so adjusted at some point by P.O

I have not measured exactly how big the starter jet measures though it is at least 1.5mm - attached is a blown up image of the starter jet, you can see there is no lip left and can see down past the brass into the aluminum tube.

I understand now this won't effect the running of the bike, how would this effect the choke operation? I guess I don't really have a baseline of how the bike ran with good gas in it to conclude if this is actually causing any issues.

Not concerned about the damage to the brass shoulder of the Jets, P.O said the carb hadn't been touched though evidence proves otherwise it seems.

I wonder if a machine shop could get the jet out and put a new one in so I could drill it.

 

Just clean it with acetone and put JBweld in it. Then drill that. It don't have to be 'brass'.

 

OP, as to your question on how choke operation will be affected, it should still work fine. You may not be able leave the choke on very long when the engine is started cold if it was drilled larger than necessary. You may have to play with the choke **** a bit after it starts cold if it's getting too much fuel while fully engaged. In other words, you fully engaged the choke by pulling it out to full choke. Then when the bike starts, you may need to manipulate the choke inward a bit to meter the fuel properly to keep the engine running properly. You should only have to do this for a few seconds as the engine warms.

OP, you mention "blipping the throttle" to help start the engine. The factory carb doesn't benefit from this as it has no accelerator pump. In fact it can make starting more difficult. Leave the throttle closed, engage the choke, and hit the button. Once it fires up you can manipulate the choke a bit if necessary to keep it running for a few seconds. Don't touch the throttle, but you can turn up the idle **** a bit after you close the choke to get a faster idle to aid warmup. Each bike is a little different on the starting sometimes, and you'll have to find out what's ideal for yours.

Also you mention "bad fuel". You're right in that you can't diagnose hard starting or proper running, and with the fresh fuel you apparently replaced it with, you should get better results. Since this carb was apparently "tuned on" by someone, I'd make sure what the numbers are on all the jets and what kind of needle and needle position is in there so you know where your tuning base is.