Kxf won't start after full rebuild?

Hi i don't know what to try anymore, my kxf 250 06 first wouldn't start easy and wouldn't idle a back fired bad so I had the valves reseated chimed correctly new piston and had the carb cleaned with all new rubbers but will not start? From trying to start the bike I've already cracked a set of crank cases and had to have them replaced which cost a fortune. Iam just gettin no where, the has a really strong spark aswell and I think is getting fuel as the plug is getting wet. Any suggestions would be great?

Are you flooding it, because carb shouldn't be to wet

I don't think so as I'm not giving it throttle but I will try turn the idle right down if it cud b gettin too much fuel thanks :)

Still no joy :/

Is the bike getting air? Not a rag stuffed in the air box?

It should be I've cleaned all the carb, air box and put a new air filter on no idea what to try next. When it has a good kik it sounds as tho it should b going but just want take and sounds as Tho it isn't gettin a spark all though the spark seems really strong any ideas would be great :)

I assuming you have checked the timing? So you installed all new valve parts and recut seats as well as top end...have you tried testing the compression or doing a leak down test to make sure there's a nice seal...the bike should still fire even if its sealing less than 90 % of the charge..


You claim the bike gets spark..try holding the plug about 10 mm from any metal surface such as a bolt..kick the bike over..there should be a bright blue spark


Next is testing to see if theres enough vacuum into the cylinder..try kicking the bike over with the ignition cap off the plug..then inspect the plug to see if its somewhat wet..


you can then try looking into the carb. if not clogged jets or sticking slide, could be a float bowl issue.. As air flows through the carb bore a pressure drop is realized and the fuel in float bowl is ‘pressurized’ as the pressure between the float bowl and the carb bore try to equalize. By altering the volume of fuel in the float bowl you’re basically varying the fuel pressure that is acting on your jets. More fuel in the float bowl will create more fuel pressure and result in rich(er) running conditions for a given set of jets.


Also check to make sure you have no air leaks..after rebuilding an 07 I got it running but would idle super load and would only mellow down if the choke was out...i then realized that air was leaking into the air box through the air boot..

Thank you verry much for your imput, It did Have a new piston and ring in so I would presume there is enough compression there and the spark is definatly jumping a good 10mm lol the timing is also spot on. I did however put all new rubbers in the carb from a kit which also came with a new float needle bit I am wondering with what you said this could have something to do with it as the little barrel bit of the carb is getting dripping wet with fuel. I will look in to what you said although it will take a lot getting my head round that aha thank you verry much for your help I will give it a look in the morning

Curious , how you cracked the crankcase's by trying to start it ?

These bikes are very picky on how they start.

a little too much fuel and they won't go.

a little to less fuel and they wont start easily.

check the float if its "Heavy" and change the shut off needle, set float height and try again,

fuel crew should be 2-2/12 turns out. needle should be 3 clip positions from the top.

choke the motor when starting giving no throttle.

ImageUploadedByThumper Talk1382616393.977210.jpg

This is the casing that craked jus from liking it trying to start it. I did change to float needle for a new one, how would I set the float hight?

Make sure the plate on the slide in the carb.isn't up, and check the big oringbon it too.

What size pilot jet are you running?


And holy crap, I've never seen a crank case crack like that from someone trying to start a bike!

From trying to get it goin so much it's been wearing me out all summer :/ aha the plates the right way with the hole to the bottom and the runner ring around it seems fine and the pilot jet is a #40. If there was a problem with the tps would this effect it or the cdi even tho it does have a good spark? Thank you all again

Will it fire from a good bump start?

IMO I don't think your issue is electrical... I would pull the carb and make sure all your o-rings and accelerator pump diaphragm are seated properly and also pull the pilot and clean it again.

Thanks for you input I've been away bt I will strip the carb again and have another look. I'm thinking it's got something to do with the carb myself just can't find what tho aha

Sent you a PM.

Edited by ryan98125

you cracked the case from starting to start it... did you replace the crank before that rebuild..looked like something was seated correctly and put pressure on the cases.. I would double/triple check timing again...leak down test too.

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