XS250 Carb Jets

[liltimpo]

Hi All,

I am based in the midlands and have a bit of a basket case xs250 1978 SE.

I am wondering if anyone has any main jets at all please? I am after #125 main jets as I am running an aftermarket exhaust but with stock air filters. I could be wrong with this size if anyone has any experience feel free to correct me. I could also do with some stock idle jets which I believe are 020 as someone has changed all my jets and made them too small.

I am really struggling to find anything as theyre odd jets. I ordered some from Japan 4 months ago and no news so far.

If anyone could help me with this it would be great. I could also do with a few other xs250 parts if anyone has some parts lying around.

Cheers all,
John

 

[CaptChrome]

Welcome to the forum.

I am running an aftermarket exhaust but with stock air filters

I am running an aftermarket exhaust and stock air filters on my xs400 and the stock jetting is just fine - are you absolutely sure you need the main jet? What operating symptoms are leading you to this conclusion (struggling to reach full rpm or bogging at wide open throttle)?

As far as sources for jets go, there is probably none better than jetsrus.com. They are in the US, so shipping cost will not be trivial, but if you are trying to get stuff from Japan, you are already committed to that.

I don't know the stock jetting for the XS250, but my advice is to get it back to stock and going down the long and winding road of tuning the crap out of the carbs with those jets before you start thinking about changing jetting and potentially going down an even longer road. Unless you have a buddy with a dyno, then pay him to tell you what you need to do .

 

[liltimpo]

Hey,

Thank you for the reply.

I would like to run the stock jetting however, whoever owed this bike before me put smaller jets in for some reason and in the UK I have found it impossible to get any jets at all standard or bigger.

The symptoms are it runs fine at idle and half throttle but when its at WOT it starts to bog down when I get to higher RPM which is not a suprise as the main is a #110 now and stock is #117.5.

 

[CaptChrome]

The symptoms are it runs fine at idle and half throttle but when its at WOT it starts to bog down when I get to higher RPM which is not a suprise as the main is a #110 now and stock is #117.5.

Yup, I agree that your main jet needs to be bigger. Well, let us know how it goes and where you end up getting the jets as it may help others in the UK/Europe in the future.

 

[Durney]

Before changing the main jet, try taking the needles out of the carb slides and LOWERING the "C" clip to the bottom position ( there are 3 notches ).
I did that to my bike and it made it drive better without killing the MPG.

 

[liltimpo]

Thanks I will have a look. I thought the needle position only made a difference up until half throttle though?

 

[CaptChrome]

I thought the needle position only made a difference up until half throttle though?

More than half throttle. More like ¾+ throttle. All the jets and the metering of the needle does contribute when you are at WOT as they are all squirting fuel into the carb throat at that point. So, adjusting the needle can't hurt, but watch that you don't get too rich in the mid-range.

I always adjust the idle mixture (pilot mix screw and pilot jet) first, then the mid-range (needle jet and jet needle shape and height) and then the WOT (main jet) mix last because of the additive effect of the slower speed jetting to the higher speed mixture.

 

[liltimpo]

Just to update you. I could not get any main jets. Even my friend in the US struggled to get any. So I gave in and brought some VM32 flatsides instead